path: root/documentation/dev-manual/dev-manual-common-tasks.xml

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[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >

<chapter id='extendpoky'>

<title>Common Tasks</title>
    <para>
        This chapter describes fundamental procedures such as creating layers,
        adding new software packages, extending or customizing images,
        porting work to new hardware (adding a new machine), and so forth.
        You will find that the procedures documented here occur often in the
        development cycle using the Yocto Project.
    </para>

    <section id="understanding-and-creating-layers">
        <title>Understanding and Creating Layers</title>

        <para>
            The OpenEmbedded build system supports organizing
            <link linkend='metadata'>Metadata</link> into multiple layers.
            Layers allow you to isolate different types of customizations from
            each other.
            You might find it tempting to keep everything in one layer when
            working on a single project.
            However, the more modular your Metadata, the easier
            it is to cope with future changes.
        </para>

        <para>
            To illustrate how layers are used to keep things modular, consider
            machine customizations.
            These types of customizations typically reside in a special layer,
            rather than a general layer, called a Board Support Package (BSP)
            Layer.
            Furthermore, the machine customizations should be isolated from
            recipes and Metadata that support a new GUI environment,
            for example.
            This situation gives you a couple of layers: one for the machine
            configurations, and one for the GUI environment.
            It is important to understand, however, that the BSP layer can
            still make machine-specific additions to recipes within the GUI
            environment layer without polluting the GUI layer itself
            with those machine-specific changes.
            You can accomplish this through a recipe that is a BitBake append
            (<filename>.bbappend</filename>) file, which is described later
            in this section.
        </para>

        <para>
        </para>

        <section id='yocto-project-layers'>
            <title>Layers</title>

            <para>
                The <link linkend='source-directory'>Source Directory</link>
                contains both general layers and BSP
                layers right out of the box.
                You can easily identify layers that ship with a
                Yocto Project release in the Source Directory by their
                folder names.
                Folders that represent layers typically have names that begin with
                the string <filename>meta-</filename>.
                <note>
                    It is not a requirement that a layer name begin with the
                    prefix <filename>meta-</filename>, but it is a commonly
                    accepted standard in the Yocto Project community.
                </note>
                For example, when you set up the Source Directory structure,
                you will see several layers:
                <filename>meta</filename>,
                <filename>meta-skeleton</filename>,
                <filename>meta-yocto</filename>, and
                <filename>meta-yocto-bsp</filename>.
                Each of these folders represents a distinct layer.
            </para>

            <para>
                As another example, if you set up a local copy of the
                <filename>meta-intel</filename> Git repository
                and then explore the folder of that general layer,
                you will discover many Intel-specific BSP layers inside.
                For more information on BSP layers, see the
                "<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>"
                section in the Yocto Project Board Support Package (BSP)
                Developer's Guide.
            </para>
        </section>

        <section id='creating-your-own-layer'>
            <title>Creating Your Own Layer</title>

            <para>
                It is very easy to create your own layers to use with the
                OpenEmbedded build system.
                The Yocto Project ships with scripts that speed up creating
                general layers and BSP layers.
                This section describes the steps you perform by hand to create
                a layer so that you can better understand them.
                For information about the layer-creation scripts, see the
                "<ulink url='&YOCTO_DOCS_BSP_URL;#creating-a-new-bsp-layer-using-the-yocto-bsp-script'>Creating a New BSP Layer Using the yocto-bsp Script</ulink>"
                section in the Yocto Project Board Support Package (BSP)
                Developer's Guide and the
                "<link linkend='creating-a-general-layer-using-the-yocto-layer-script'>Creating a General Layer Using the yocto-layer Script</link>"
                section further down in this manual.
            </para>

            <para>
                Follow these general steps to create your layer:
                <orderedlist>
                    <listitem><para><emphasis>Check Existing Layers:</emphasis>
                        Before creating a new layer, you should be sure someone
                        has not already created a layer containing the Metadata
                        you need.
                        You can see the
                        <ulink url='http://layers.openembedded.org/layerindex/layers/'><filename>OpenEmbedded Metadata Index</filename></ulink>
                        for a list of layers from the OpenEmbedded community
                        that can be used in the Yocto Project.
                        </para></listitem>
                    <listitem><para><emphasis>Create a Directory:</emphasis>
                        Create the directory for your layer.
                        While not strictly required, prepend the name of the
                        folder with the string <filename>meta-</filename>.
                        For example:
                        <literallayout class='monospaced'>
     meta-mylayer
     meta-GUI_xyz
     meta-mymachine
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Create a Layer Configuration
                       File:</emphasis>
                       Inside your new layer folder, you need to create a
                       <filename>conf/layer.conf</filename> file.
                       It is easiest to take an existing layer configuration
                       file and copy that to your layer's
                       <filename>conf</filename> directory and then modify the
                       file as needed.</para>
                       <para>The
                       <filename>meta-yocto-bsp/conf/layer.conf</filename> file
                       demonstrates the required syntax:
                       <literallayout class='monospaced'>
     # We have a conf and classes directory, add to BBPATH
     BBPATH .= ":${LAYERDIR}"

     # We have recipes-* directories, add to BBFILES
     BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
                 ${LAYERDIR}/recipes-*/*/*.bbappend"

     BBFILE_COLLECTIONS += "yoctobsp"
     BBFILE_PATTERN_yoctobsp = "^${LAYERDIR}/"
     BBFILE_PRIORITY_yoctobsp = "5"
     LAYERVERSION_yoctobsp = "2"
                        </literallayout></para>
                        <para>Here is an explanation of the example:
                        <itemizedlist>
                            <listitem><para>The configuration and
                                classes directory is appended to
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-BBPATH'><filename>BBPATH</filename></ulink>.
                                <note>
                                    All non-distro layers, which include all BSP
                                    layers, are expected to append the layer
                                    directory to the
                                    <filename>BBPATH</filename>.
                                    On the other hand, distro layers, such as
                                    <filename>meta-yocto</filename>, can choose
                                    to enforce their own precedence over
                                    <filename>BBPATH</filename>.
                                    For an example of that syntax, see the
                                    <filename>layer.conf</filename> file for
                                    the <filename>meta-yocto</filename> layer.
                                </note></para></listitem>
                            <listitem><para>The recipes for the layers are
                                appended to
                                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILES'>BBFILES</ulink></filename>.
                                </para></listitem>
                            <listitem><para>The
                                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_COLLECTIONS'>BBFILE_COLLECTIONS</ulink></filename>
                                variable is then appended with the layer name.
                                </para></listitem>
                            <listitem><para>The
                                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PATTERN'>BBFILE_PATTERN</ulink></filename>
                                variable is set to a regular expression and is
                                used to match files from
                                <filename>BBFILES</filename> into a particular
                                layer.
                                In this case,
                                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LAYERDIR'>LAYERDIR</ulink></filename>
                                is used to make <filename>BBFILE_PATTERN</filename> match within the
                                layer's path.</para></listitem>
                            <listitem><para>The
                                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PRIORITY'>BBFILE_PRIORITY</ulink></filename>
                                variable then assigns a priority to the layer.
                                Applying priorities is useful in situations
                                where the same package might appear in multiple
                                layers and allows you to choose the layer
                                that takes precedence.</para></listitem>
                            <listitem><para>The
                                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LAYERVERSION'>LAYERVERSION</ulink></filename>
                                variable optionally specifies the version of a
                                layer as a single number.</para></listitem>
                        </itemizedlist></para>
                        <para>Note the use of the
                        <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LAYERDIR'>LAYERDIR</ulink></filename>
                        variable, which expands to the directory of the current
                        layer.</para>
                        <para>Through the use of the <filename>BBPATH</filename>
                        variable, BitBake locates class files
                        (<filename>.bbclass</filename>),
                        configuration files, and files that are included
                        with <filename>include</filename> and
                        <filename>require</filename> statements.
                        For these cases, BitBake uses the first file that
                        matches the name found in <filename>BBPATH</filename>.
                        This is similar to the way the <filename>PATH</filename>
                        variable is used for binaries.
                        It is recommended, therefore, that you use unique
                        class and configuration
                        filenames in your custom layer.</para></listitem>
                    <listitem><para><emphasis>Add Content:</emphasis> Depending
                        on the type of layer, add the content.
                        If the layer adds support for a machine, add the machine
                        configuration in a <filename>conf/machine/</filename>
                        file within the layer.
                        If the layer adds distro policy, add the distro
                        configuration in a <filename>conf/distro/</filename>
                        file within the layer.
                        If the layer introduces new recipes, put the recipes
                        you need in <filename>recipes-*</filename>
                        subdirectories within the layer.
                        <note>In order to be compliant with the Yocto Project,
                            a layer must contain a
                            <ulink url='&YOCTO_DOCS_BSP_URL;#bsp-filelayout-readme'>README file.</ulink>
                            </note></para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='best-practices-to-follow-when-creating-layers'>
            <title>Best Practices to Follow When Creating Layers</title>

            <para>
                To create layers that are easier to maintain and that will
                not impact builds for other machines, you should consider the
                information in the following sections.
            </para>

            <section id='avoid-overlaying-entire-recipes'>
                <title>Avoid "Overlaying" Entire Recipes</title>

                <para>
                    Avoid "overlaying" entire recipes from other layers in your
                    configuration.
                    In other words, do not copy an entire recipe into your
                    layer and then modify it.
                    Rather, use an append file (<filename>.bbappend</filename>)
                    to override
                    only those parts of the original recipe you need to modify.
                </para>
            </section>

            <section id='avoid-duplicating-include-files'>
                <title>Avoid Duplicating Include Files</title>

                <para>
                    Avoid duplicating include files.
                    Use append files (<filename>.bbappend</filename>)
                    for each recipe
                    that uses an include file.
                    Or, if you are introducing a new recipe that requires
                    the included file, use the path relative to the original
                    layer directory to refer to the file.
                    For example, use
                    <filename>require recipes-core/somepackage/somefile.inc</filename>
                    instead of <filename>require somefile.inc</filename>.
                    If you're finding you have to overlay the include file,
                    it could indicate a deficiency in the include file in
                    the layer to which it originally belongs.
                    If this is the case, you need to address that deficiency
                    instead of overlaying the include file.
                </para>

                <para>
                    For example, consider how support plug-ins for the Qt 4
                    database are configured.
                    The Source Directory does not have MySQL or PostgreSQL.
                    However, OpenEmbedded's layer <filename>meta-oe</filename>
                    does.
                    Consequently, <filename>meta-oe</filename> uses
                    append files to modify the
                    <filename>QT_SQL_DRIVER_FLAGS</filename> variable to
                    enable the appropriate plug-ins.
                    This variable was added to the <filename>qt4.inc</filename>
                    include file in the Source Directory specifically to allow
                    the <filename>meta-oe</filename> layer to be able to control
                    which plug-ins are built.
                </para>
            </section>

            <section id='structure-your-layers'>
                <title>Structure Your Layers</title>

                <para>
                    Proper use of overrides within append files and placement
                    of machine-specific files within your layer can ensure that
                    a build is not using the wrong Metadata and negatively
                    impacting a build for a different machine.
                    Following are some examples:
                    <itemizedlist>
                        <listitem><para><emphasis>Modifying Variables to Support
                            a Different Machine:</emphasis>
                            Suppose you have a layer named
                            <filename>meta-one</filename> that adds support
                            for building machine "one".
                            To do so, you use an append file named
                            <filename>base-files.bbappend</filename> and
                            create a dependency on "foo" by altering the
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
                            variable:
                            <literallayout class='monospaced'>
     DEPENDS = "foo"
                            </literallayout>
                            The dependency is created during any build that
                            includes the layer
                            <filename>meta-one</filename>.
                            However, you might not want this dependency
                            for all machines.
                            For example, suppose you are building for
                            machine "two" but your
                            <filename>bblayers.conf</filename> file has the
                            <filename>meta-one</filename> layer included.
                            During the build, the
                            <filename>base-files</filename> for machine
                            "two" will also have the dependency on
                            <filename>foo</filename>.</para>
                            <para>To make sure your changes apply only when
                            building machine "one", use a machine override
                            with the <filename>DEPENDS</filename> statement:
                            <literallayout class='monospaced'>
     DEPENDS_one = "foo"
                            </literallayout>
                            You should follow the same strategy when using
                            <filename>_append</filename> and
                            <filename>_prepend</filename> operations:
                            <literallayout class='monospaced'>
     DEPENDS_append_one = " foo"
     DEPENDS_prepend_one = "foo "
                            </literallayout>
                            <note>
                                Avoiding "+=" and "=+" and using
                                machine-specific
                                <filename>_append</filename>
                                and <filename>_prepend</filename> operations
                                is recommended as well.
                            </note></para></listitem>
                        <listitem><para><emphasis>Place Machine-Specific Files
                            in Machine-Specific Locations:</emphasis>
                            When you have a base recipe, such as
                            <filename>base-files.bb</filename>, that
                            contains a
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                            statement to a file, you can use an append file
                            to cause the build to use your own version of
                            the file.
                            For example, an append file in your layer at
                            <filename>meta-one/recipes-core/base-files/base-files.bbappend</filename>
                            could extend
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink>
                            using
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
                            as follows:
                            <literallayout class='monospaced'>
     FILESEXTRAPATHS_prepend := "${THISDIR}/${BPN}:"
                            </literallayout>
                            The build for machine "one" will pick up your
                            machine-specific file as long as you have the
                            file in
                            <filename>meta-one/recipes-core/base-files/base-files/</filename>.
                            However, if you are building for a different
                            machine and the
                            <filename>bblayers.conf</filename> file includes
                            the <filename>meta-one</filename> layer and
                            the location of your machine-specific file is
                            the first location where that file is found
                            according to <filename>FILESPATH</filename>,
                            builds for all machines will also use that
                            machine-specific file.</para>
                            <para>You can make sure that a machine-specific
                            file is used for a particular machine by putting
                            the file in a subdirectory specific to the
                            machine.
                            For example, rather than placing the file in
                            <filename>meta-one/recipes-core/base-files/base-files/</filename>
                            as shown above, put it in
                            <filename>meta-one/recipes-core/base-files/base-files/one/</filename>.
                            Not only does this make sure the file is used
                            only when building for machine "one", but the
                            build process locates the file more quickly.</para>
                            <para>In summary, you need to place all files
                            referenced from <filename>SRC_URI</filename>
                            in a machine-specific subdirectory within the
                            layer in order to restrict those files to
                            machine-specific builds.</para></listitem>
                    </itemizedlist>
                </para>
            </section>

            <section id='other-recommendations'>
                <title>Other Recommendations</title>

                <para>
                    We also recommend the following:
                    <itemizedlist>
                        <listitem><para>Store custom layers in a Git repository
                            that uses the
                            <filename>meta-&lt;layer_name&gt;</filename> format.
                            </para></listitem>
                        <listitem><para>Clone the repository alongside other
                            <filename>meta</filename> directories in the
                            <link linkend='source-directory'>Source Directory</link>.
                            </para></listitem>
                     </itemizedlist>
                     Following these recommendations keeps your Source Directory and
                     its configuration entirely inside the Yocto Project's core
                     base.
                </para>
            </section>
        </section>

        <section id='enabling-your-layer'>
            <title>Enabling Your Layer</title>

            <para>
                Before the OpenEmbedded build system can use your new layer,
                you need to enable it.
                To enable your layer, simply add your layer's path to the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBLAYERS'>BBLAYERS</ulink></filename>
                variable in your <filename>conf/bblayers.conf</filename> file,
                which is found in the
                <link linkend='build-directory'>Build Directory</link>.
                The following example shows how to enable a layer named
                <filename>meta-mylayer</filename>:
                <literallayout class='monospaced'>
     LCONF_VERSION = "6"

     BBPATH = "${TOPDIR}"
     BBFILES ?= ""

     BBLAYERS ?= " \
       $HOME/poky/meta \
       $HOME/poky/meta-yocto \
       $HOME/poky/meta-yocto-bsp \
       $HOME/poky/meta-mylayer \
       "

     BBLAYERS_NON_REMOVABLE ?= " \
       $HOME/poky/meta \
       $HOME/poky/meta-yocto \
       "
                </literallayout>
            </para>

            <para>
                BitBake parses each <filename>conf/layer.conf</filename> file
                as specified in the <filename>BBLAYERS</filename> variable
                within the <filename>conf/bblayers.conf</filename> file.
                During the processing of each
                <filename>conf/layer.conf</filename> file, BitBake adds the
                recipes, classes and configurations contained within the
                particular layer to the source directory.
            </para>
        </section>

        <section id='using-bbappend-files'>
            <title>Using .bbappend Files</title>

            <para>
                Recipes used to append Metadata to other recipes are called
                BitBake append files.
                BitBake append files use the <filename>.bbappend</filename> file
                type suffix, while the corresponding recipes to which Metadata
                is being appended use the <filename>.bb</filename> file type
                suffix.
            </para>

            <para>
                A <filename>.bbappend</filename> file allows your layer to make
                additions or changes to the content of another layer's recipe
                without having to copy the other recipe into your layer.
                Your <filename>.bbappend</filename> file resides in your layer,
                while the main <filename>.bb</filename> recipe file to
                which you are appending Metadata resides in a different layer.
            </para>

            <para>
                Append files must have the same root names as their corresponding
                recipes.
                For example, the append file
                <filename>someapp_&DISTRO;.bbappend</filename> must apply to
                <filename>someapp_&DISTRO;.bb</filename>.
                This means the original recipe and append file names are version
                number-specific.
                If the corresponding recipe is renamed to update to a newer
                version, the corresponding <filename>.bbappend</filename> file must
                be renamed (and possibly updated) as well.
                During the build process, BitBake displays an error on starting
                if it detects a <filename>.bbappend</filename> file that does
                not have a corresponding recipe with a matching name.
                See the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BB_DANGLINGAPPENDS_WARNONLY'><filename>BB_DANGLINGAPPENDS_WARNONLY</filename></ulink>
                variable for information on how to handle this error.
            </para>

            <para>
                Being able to append information to an existing recipe not only
                avoids duplication, but also automatically applies recipe
                changes in a different layer to your layer.
                If you were copying recipes, you would have to manually merge
                changes as they occur.
            </para>

            <para>
                As an example, consider the main formfactor recipe and a
                corresponding formfactor append file both from the
                <link linkend='source-directory'>Source Directory</link>.
                Here is the main formfactor recipe, which is named
                <filename>formfactor_0.0.bb</filename> and located in the
                "meta" layer at
                <filename>meta/recipes-bsp/formfactor</filename>:
                <literallayout class='monospaced'>
     SUMMARY = "Device formfactor information"
     SECTION = "base"
     LICENSE = "MIT"
     LIC_FILES_CHKSUM = "file://${COREBASE}/LICENSE;md5=4d92cd373abda3937c2bc47fbc49d690 \
                    file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420"
     PR = "r44"

     SRC_URI = "file://config file://machconfig"
     S = "${WORKDIR}"

     PACKAGE_ARCH = "${MACHINE_ARCH}"
     INHIBIT_DEFAULT_DEPS = "1"

     do_install() {
	     # Only install file if it has a contents
             install -d ${D}${sysconfdir}/formfactor/
             install -m 0644 ${S}/config ${D}${sysconfdir}/formfactor/
	     if [ -s "${S}/machconfig" ]; then
	             install -m 0644 ${S}/machconfig ${D}${sysconfdir}/formfactor/
	     fi
     }
                </literallayout>
                In the main recipe, note the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                variable, which tells the OpenEmbedded build system where to
                find files during the build.
            </para>

            <para>
                Following is the append file, which is named
                <filename>formfactor_0.0.bbappend</filename> and is from the
                Crown Bay BSP Layer named
                <filename>meta-intel/meta-crownbay</filename>.
                The file is in <filename>recipes-bsp/formfactor</filename>:
                <literallayout class='monospaced'>
     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
                </literallayout>
            </para>

            <para>
                By default, the build system uses the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink>
                variable to locate files.
                This append file extends the locations by setting the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
                variable.
                Setting this variable in the <filename>.bbappend</filename>
                file is the most reliable and recommended method for adding
                directories to the search path used by the build system
                to find files.
            </para>

            <para>
                The statement in this example extends the directories to include
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-THISDIR'><filename>THISDIR</filename></ulink><filename>}/${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink><filename>}</filename>,
                which resolves to a directory named
                <filename>formfactor</filename> in the same directory
                in which the append file resides (i.e.
                <filename>meta-intel/meta-crownbay/recipes-bsp/formfactor/formfactor</filename>.
                This implies that you must have the supporting directory
                structure set up that will contain any files or patches you
                will be including from the layer.
            </para>

            <para>
                Using the immediate expansion assignment operator
                <filename>:=</filename> is important because of the reference to
                <filename>THISDIR</filename>.
                The trailing colon character is important as it ensures that
                items in the list remain colon-separated.
                <note>
                    <para>
                        BitBake automatically defines the
                        <filename>THISDIR</filename> variable.
                        You should never set this variable yourself.
                        Using "_prepend" ensures your path will
                        be searched prior to other paths in the final list.
                    </para>

                    <para>
                        Also, not all append files add extra files.
                        Many append files simply exist to add build options
                        (e.g. <filename>systemd</filename>).
                        For these cases, it is not necessary to use the
                        "_prepend" part of the statement.
                    </para>
                </note>
            </para>
        </section>

        <section id='prioritizing-your-layer'>
            <title>Prioritizing Your Layer</title>

            <para>
                Each layer is assigned a priority value.
                Priority values control which layer takes precedence if there
                are recipe files with the same name in multiple layers.
                For these cases, the recipe file from the layer with a higher
                priority number takes precedence.
                Priority values also affect the order in which multiple
                <filename>.bbappend</filename> files for the same recipe are
                applied.
                You can either specify the priority manually, or allow the
                build system to calculate it based on the layer's dependencies.
            </para>

            <para>
                To specify the layer's priority manually, use the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PRIORITY'><filename>BBFILE_PRIORITY</filename></ulink>
                variable.
                For example:
                <literallayout class='monospaced'>
     BBFILE_PRIORITY_mylayer = "1"
                </literallayout>
            </para>

            <note>
                <para>It is possible for a recipe with a lower version number
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
                in a layer that has a higher priority to take precedence.</para>
                <para>Also, the layer priority does not currently affect the
                precedence order of <filename>.conf</filename>
                or <filename>.bbclass</filename> files.
                Future versions of BitBake might address this.</para>
            </note>
        </section>

        <section id='managing-layers'>
            <title>Managing Layers</title>

            <para>
                You can use the BitBake layer management tool to provide a view
                into the structure of recipes across a multi-layer project.
                Being able to generate output that reports on configured layers
                with their paths and priorities and on
                <filename>.bbappend</filename> files and their applicable
                recipes can help to reveal potential problems.
            </para>

            <para>
                Use the following form when running the layer management tool.
                <literallayout class='monospaced'>
     $ bitbake-layers &lt;command&gt; [arguments]
                </literallayout>
                The following list describes the available commands:
                <itemizedlist>
                    <listitem><para><filename><emphasis>help:</emphasis></filename>
                        Displays general help or help on a specified command.
                        </para></listitem>
                    <listitem><para><filename><emphasis>show-layers:</emphasis></filename>
                        Shows the current configured layers.
                        </para></listitem>
                    <listitem><para><filename><emphasis>show-recipes:</emphasis></filename>
                        Lists available recipes and the layers that provide them.
                        </para></listitem>
                    <listitem><para><filename><emphasis>show-overlayed:</emphasis></filename>
                        Lists overlayed recipes.
                        A recipe is overlayed when a recipe with the same name
                        exists in another layer that has a higher layer
                        priority.
                        </para></listitem>
                    <listitem><para><filename><emphasis>show-appends:</emphasis></filename>
                        Lists <filename>.bbappend</filename> files and the
                        recipe files to which they apply.
                        </para></listitem>
                    <listitem><para><filename><emphasis>show-cross-depends:</emphasis></filename>
                        Lists dependency relationships between recipes that
                        cross layer boundaries.
                        </para></listitem>
                    <listitem><para><filename><emphasis>flatten:</emphasis></filename>
                        Flattens the layer configuration into a separate output
                        directory.
                        Flattening your layer configuration builds a "flattened"
                        directory that contains the contents of all layers,
                        with any overlayed recipes removed and any
                        <filename>.bbappend</filename> files appended to the
                        corresponding recipes.
                        You might have to perform some manual cleanup of the
                        flattened layer as follows:
                        <itemizedlist>
                            <listitem><para>Non-recipe files (such as patches)
                                are overwritten.
                                The flatten command shows a warning for these
                                files.
                                </para></listitem>
                            <listitem><para>Anything beyond the normal layer
                                setup has been added to the
                                <filename>layer.conf</filename> file.
                                Only the lowest priority layer's
                                <filename>layer.conf</filename> is used.
                                </para></listitem>
                            <listitem><para>Overridden and appended items from
                                <filename>.bbappend</filename> files need to be
                                cleaned up.
                                The contents of each
                                <filename>.bbappend</filename> end up in the
                                flattened recipe.
                                However, if there are appended or changed
                                variable values, you need to tidy these up
                                yourself.
                                Consider the following example.
                                Here, the <filename>bitbake-layers</filename>
                                command adds the line
                                <filename>#### bbappended ...</filename> so that
                                you know where the following lines originate:
                                <literallayout class='monospaced'>
     ...
     DESCRIPTION = "A useful utility"
     ...
     EXTRA_OECONF = "--enable-something"
     ...

     #### bbappended from meta-anotherlayer ####

     DESCRIPTION = "Customized utility"
     EXTRA_OECONF += "--enable-somethingelse"
                                </literallayout>
                                Ideally, you would tidy up these utilities as
                                follows:
                                <literallayout class='monospaced'>
     ...
     DESCRIPTION = "Customized utility"
     ...
     EXTRA_OECONF = "--enable-something --enable-somethingelse"
     ...
                                </literallayout></para></listitem>
                        </itemizedlist></para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='creating-a-general-layer-using-the-yocto-layer-script'>
            <title>Creating a General Layer Using the yocto-layer Script</title>

            <para>
                The <filename>yocto-layer</filename> script simplifies
                creating a new general layer.
                <note>
                    For information on BSP layers, see the
                    "<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>"
                    section in the Yocto Project Board Specific (BSP)
                    Developer's Guide.
                </note>
                The default mode of the script's operation is to prompt you for
                information needed to generate the layer:
                <itemizedlist>
                    <listitem><para>The layer priority
                        </para></listitem>
                    <listitem><para>Whether or not to create a sample recipe.
                        </para></listitem>
                    <listitem><para>Whether or not to create a sample
                        append file.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                Use the <filename>yocto-layer create</filename> sub-command
                to create a new general layer.
                In its simplest form, you can create a layer as follows:
                <literallayout class='monospaced'>
     $ yocto-layer create mylayer
                </literallayout>
                The previous example creates a layer named
                <filename>meta-mylayer</filename> in the current directory.
            </para>

            <para>
                As the <filename>yocto-layer create</filename> command runs,
                default values for the prompts appear in brackets.
                Pressing enter without supplying anything for the prompts
                or pressing enter and providing an invalid response causes the
                script to accept the default value.
                Once the script completes, the new layer
                is created in the current working directory.
                The script names the layer by prepending
                <filename>meta-</filename> to the name you provide.
            </para>

            <para>
                Minimally, the script creates the following within the layer:
                <itemizedlist>
                    <listitem><para><emphasis>The <filename>conf</filename>
                        directory:</emphasis>
                        This directory contains the layer's configuration file.
                        The root name for the file is the same as the root name
                        your provided for the layer (e.g.
                        <filename>&lt;layer&gt;.conf</filename>).
                        </para></listitem>
                    <listitem><para><emphasis>The
                        <filename>COPYING.MIT</filename> file:</emphasis>
                        The copyright and use notice for the software.
                        </para></listitem>
                    <listitem><para><emphasis>The <filename>README</filename>
                        file:</emphasis>
                        A file describing the contents of your new layer.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                If you choose to generate a sample recipe file, the script
                prompts you for the name for the recipe and then creates it
                in <filename>&lt;layer&gt;/recipes-example/example/</filename>.
                The script creates a <filename>.bb</filename> file and a
                directory, which contains a sample
                <filename>helloworld.c</filename> source file, along with
                a sample patch file.
                If you do not provide a recipe name, the script uses
                "example".
            </para>

            <para>
                If you choose to generate a sample append file, the script
                prompts you for the name for the file and then creates it
                in <filename>&lt;layer&gt;/recipes-example-bbappend/example-bbappend/</filename>.
                The script creates a <filename>.bbappend</filename> file and a
                directory, which contains a sample patch file.
                If you do not provide a recipe name, the script uses
                "example".
                The script also prompts you for the version of the append file.
                The version should match the recipe to which the append file
                is associated.
            </para>

            <para>
                The easiest way to see how the <filename>yocto-layer</filename>
                script works is to experiment with the script.
                You can also read the usage information by entering the
                following:
                <literallayout class='monospaced'>
     $ yocto-layer help
                </literallayout>
            </para>

            <para>
                Once you create your general layer, you must add it to your
                <filename>bblayers.conf</filename> file.
                Here is an example where a layer named
                <filename>meta-mylayer</filename> is added:
                <literallayout class='monospaced'>
     BBLAYERS = ?" \
        /usr/local/src/yocto/meta \
        /usr/local/src/yocto/meta-yocto \
        /usr/local/src/yocto/meta-yocto-bsp \
        /usr/local/src/yocto/meta-mylayer \
        "

     BBLAYERS_NON_REMOVABLE ?= " \
        /usr/local/src/yocto/meta \
        /usr/local/src/yocto/meta-yocto \
        "
                </literallayout>
                Adding the layer to this file enables the build system to
                locate the layer during the build.
                </para>
        </section>
    </section>

    <section id='usingpoky-extend-customimage'>
        <title>Customizing Images</title>

        <para>
            You can customize images to satisfy particular requirements.
            This section describes several methods and provides guidelines for each.
        </para>

        <section id='usingpoky-extend-customimage-localconf'>
            <title>Customizing Images Using <filename>local.conf</filename></title>

            <para>
                Probably the easiest way to customize an image is to add a
                package by way of the <filename>local.conf</filename>
                configuration file.
                Because it is limited to local use, this method generally only
                allows you to add packages and is not as flexible as creating
                your own customized image.
                When you add packages using local variables this way, you need
                to realize that these variable changes are in effect for every
                build and consequently affect all images, which might not
                be what you require.
            </para>

            <para>
                To add a package to your image using the local configuration
                file, use the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'>IMAGE_INSTALL</ulink></filename>
                variable with the <filename>_append</filename> operator:
                <literallayout class='monospaced'>
     IMAGE_INSTALL_append = " strace"
                </literallayout>
                Use of the syntax is important - specifically, the space between
                the quote and the package name, which is
                <filename>strace</filename> in this example.
                This space is required since the <filename>_append</filename>
                operator does not add the space.
            </para>

            <para>
                Furthermore, you must use <filename>_append</filename> instead
                of the <filename>+=</filename> operator if you want to avoid
                ordering issues.
                The reason for this is because doing so unconditionally appends
                to the variable and avoids ordering problems due to the
                variable being set in image recipes and
                <filename>.bbclass</filename> files with operators like
                <filename>?=</filename>.
                Using <filename>_append</filename> ensures the operation takes
                affect.
            </para>

            <para>
                As shown in its simplest use,
                <filename>IMAGE_INSTALL_append</filename> affects all images.
                It is possible to extend the syntax so that the variable
                applies to a specific image only.
                Here is an example:
                <literallayout class='monospaced'>
     IMAGE_INSTALL_append_pn-core-image-minimal = " strace"
                </literallayout>
                This example adds <filename>strace</filename> to the
                <filename>core-image-minimal</filename> image only.
            </para>

            <para>
                You can add packages using a similar approach through the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-CORE_IMAGE_EXTRA_INSTALL'>CORE_IMAGE_EXTRA_INSTALL</ulink></filename>
                variable.
                If you use this variable, only
                <filename>core-image-*</filename> images are affected.
            </para>
        </section>

        <section id='usingpoky-extend-customimage-imagefeatures'>
            <title>Customizing Images Using Custom <filename>IMAGE_FEATURES</filename> and
                <filename>EXTRA_IMAGE_FEATURES</filename></title>

            <para>
                Another method for customizing your image is to enable or
                disable high-level image features by using the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
                and <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_IMAGE_FEATURES'><filename>EXTRA_IMAGE_FEATURES</filename></ulink>
                variables.
                Although the functions for both variables are nearly equivalent,
                best practices dictate using <filename>IMAGE_FEATURES</filename>
                from within a recipe and using
                <filename>EXTRA_IMAGE_FEATURES</filename> from within
                your <filename>local.conf</filename> file, which is found in the
                <link linkend='build-directory'>Build Directory</link>.
            </para>

            <para>
                To understand how these features work, the best reference is
                <filename>meta/classes/core-image.bbclass</filename>.
                In summary, the file looks at the contents of the
                <filename>IMAGE_FEATURES</filename> variable and then maps
                those contents into a set of package groups.
                Based on this information, the build system automatically
                adds the appropriate packages to the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'><filename>IMAGE_INSTALL</filename></ulink>
                variable.
                Effectively, you are enabling extra features by extending the
                class or creating a custom class for use with specialized image
                <filename>.bb</filename> files.
            </para>

            <para>
                Use the <filename>EXTRA_IMAGE_FEATURES</filename> variable
                from within your local configuration file.
                Using a separate area from which to enable features with
                this variable helps you avoid overwriting the features in the
                image recipe that are enabled with
                <filename>IMAGE_FEATURES</filename>.
                The value of <filename>EXTRA_IMAGE_FEATURES</filename> is added
                to <filename>IMAGE_FEATURES</filename> within
                <filename>meta/conf/bitbake.conf</filename>.
            </para>

            <para>
                To illustrate how you can use these variables to modify your
                image, consider an example that selects the SSH server.
                The Yocto Project ships with two SSH servers you can use
                with your images: Dropbear and OpenSSH.
                Dropbear is a minimal SSH server appropriate for
                resource-constrained environments, while OpenSSH is a
                well-known standard SSH server implementation.
                By default, the <filename>core-image-sato</filename> image
                is configured to use Dropbear.
                The <filename>core-image-full-cmdline</filename> and
                <filename>core-image-lsb</filename> images both
                include OpenSSH.
                The <filename>core-image-minimal</filename> image does not
                contain an SSH server.
            </para>

            <para>
                You can customize your image and change these defaults.
                Edit the <filename>IMAGE_FEATURES</filename> variable
                in your recipe or use the
                <filename>EXTRA_IMAGE_FEATURES</filename> in your
                <filename>local.conf</filename> file so that it configures the
                image you are working with to include
                <filename>ssh-server-dropbear</filename> or
                <filename>ssh-server-openssh</filename>.
            </para>

            <note>
                See the
                "<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>"
                section in the Yocto Project Reference Manual for a complete
                list of image features that ship with the Yocto Project.
            </note>
        </section>

        <section id='usingpoky-extend-customimage-custombb'>
            <title>Customizing Images Using Custom .bb Files</title>

            <para>
                You can also customize an image by creating a custom recipe
                that defines additional software as part of the image.
                The following example shows the form for the two lines you need:
                <literallayout class='monospaced'>
     IMAGE_INSTALL = "packagegroup-core-x11-base package1 package2"

     inherit core-image
                </literallayout>
            </para>

            <para>
                Defining the software using a custom recipe gives you total
                control over the contents of the image.
                It is important to use the correct names of packages in the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'>IMAGE_INSTALL</ulink></filename>
                variable.
                You must use the OpenEmbedded notation and not the Debian notation for the names
                (e.g. <filename>eglibc-dev</filename> instead of <filename>libc6-dev</filename>).
            </para>

            <para>
                The other method for creating a custom image is to base it on an existing image.
                For example, if you want to create an image based on <filename>core-image-sato</filename>
                but add the additional package <filename>strace</filename> to the image,
                copy the <filename>meta/recipes-sato/images/core-image-sato.bb</filename> to a
                new <filename>.bb</filename> and add the following line to the end of the copy:
                <literallayout class='monospaced'>
     IMAGE_INSTALL += "strace"
                </literallayout>
            </para>
        </section>

        <section id='usingpoky-extend-customimage-customtasks'>
            <title>Customizing Images Using Custom Package Groups</title>

            <para>
                For complex custom images, the best approach for customizing
                an image is to create a custom package group recipe that is
                used to build the image or images.
                A good example of a package group recipe is
                <filename>meta/recipes-core/packagegroups/packagegroup-core-boot.bb</filename>.
                The
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'>PACKAGES</ulink></filename>
                variable lists the package group packages you wish to produce.
                <filename>inherit packagegroup</filename> sets appropriate
                default values and automatically adds <filename>-dev</filename>,
                <filename>-dbg</filename>, and <filename>-ptest</filename>
                complementary packages for every package specified in
                <filename>PACKAGES</filename>.
                Note that the inherit line should be towards
                the top of the recipe, certainly before you set
                <filename>PACKAGES</filename>.
                For each package you specify in <filename>PACKAGES</filename>,
                you can use
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'>RDEPENDS</ulink></filename>
                and
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'>RRECOMMENDS</ulink></filename>
                entries to provide a list of packages the parent task package
                should contain.
                Following is an example:
                <literallayout class='monospaced'>
     DESCRIPTION = "My Custom Package Groups"

     inherit packagegroup

     PACKAGES = "\
         packagegroup-custom-apps \
         packagegroup-custom-tools \
         "

     RDEPENDS_packagegroup-custom-apps = "\
         dropbear \
         portmap \
         psplash"

     RDEPENDS_packagegroup-custom-tools = "\
         oprofile \
         oprofileui-server \
         lttng-control \
         lttng-viewer"

     RRECOMMENDS_packagegroup-custom-tools = "\
         kernel-module-oprofile"
                </literallayout>
            </para>

            <para>
                In the previous example, two package group packages are created with their dependencies and their
                recommended package dependencies listed: <filename>packagegroup-custom-apps</filename>, and
                <filename>packagegroup-custom-tools</filename>.
                To build an image using these package group packages, you need to add
                <filename>packagegroup-custom-apps</filename> and/or
                <filename>packagegroup-custom-tools</filename> to
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'>IMAGE_INSTALL</ulink></filename>.
                For other forms of image dependencies see the other areas of this section.
            </para>
        </section>
    </section>

    <section id='new-recipe-writing-a-new-recipe'>
        <title>Writing a New Recipe</title>

        <para>
            Recipes (<filename>.bb</filename> files) are fundamental components
            in the Yocto Project environment.
            Each software component built by the OpenEmbedded build system
            requires a recipe to define the component.
            This section describes how to create, write, and test a new
            recipe.
            <note>
                For information on variables that are useful for recipes and
                for information about recipe naming issues, see the
                "<ulink url='&YOCTO_DOCS_REF_URL;#ref-varlocality-recipe-required'>Required</ulink>"
                section of the Yocto Project Reference Manual.
            </note>
        </para>

        <section id='new-recipe-overview'>
            <title>Overview</title>

            <para>
                The following figure shows the basic process for creating a
                new recipe.
                The remainder of the section provides details for the steps.
                <imagedata fileref="figures/recipe-workflow.png" width="6in" depth="7in" align="center" scalefit="1" />
            </para>
        </section>

        <section id='new-recipe-locate-a-base-recipe'>
            <title>Locate a Base Recipe</title>

            <para>
                Before writing a recipe from scratch, it is often useful to
                discover whether someone else has already written one that
                meets (or comes close to meeting) your needs.
                The Yocto Project and OpenEmbedded communities maintain many
                recipes that might be candidates for what you are doing.
                You can find a good central index of these recipes in the
                <ulink url='http://layers.openembedded.org'>OpenEmbedded metadata index</ulink>.
            </para>

            <para>
                Working from an existing recipe or a skeleton recipe is the
                best way to get started.
                Here are some points on both methods:
                <itemizedlist>
                    <listitem><para><emphasis>Locate and modify a recipe that
                        is close to what you want to do:</emphasis>
                        This method works when you are familiar with the
                        current recipe space.
                        The method does not work so well for those new to
                        the Yocto Project or writing recipes.</para>
                        <para>Some risks associated with this method are
                        using a recipe that has areas totally unrelated to
                        what you are trying to accomplish with your recipe,
                        not recognizing areas of the recipe that you might
                        have to add from scratch, and so forth.
                        All these risks stem from unfamiliarity with the
                        existing recipe space.</para></listitem>
                    <listitem><para><emphasis>Use and modify the following
                        skeleton recipe:</emphasis>
                        <literallayout class='monospaced'>
     SUMMARY = ""
     HOMEPAGE = ""
     LICENSE = ""

     LIC_FILES_CHKSUM = ""

     SRC_URI = ""
     SRC_URI[md5sum] = ""
     SRC_URI[sha256sum] = ""

     S = "${WORKDIR}/${PN}-${PV}"

     inherit &lt;stuff&gt;
                        </literallayout>
                        Modifying this recipe is the recommended method for
                        creating a new recipe.
                        The recipe provides the fundamental areas that you need
                        to include, exclude, or alter to fit your needs.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='new-recipe-storing-and-naming-the-recipe'>
            <title>Storing and Naming the Recipe</title>

            <para>
                Once you have your base recipe, you should put it in your
                own layer and name it appropriately.
                Locating it correctly ensures that the OpenEmbedded build
                system can find it when you use BitBake to process the
                recipe.
            </para>

            <itemizedlist>
                <listitem><para><emphasis>Storing Your Recipe:</emphasis>
                    The OpenEmbedded build system locates your recipe
                    through the layer's <filename>conf/layer.conf</filename>
                    file and the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILES'><filename>BBFILES</filename></ulink>
                    variable.
                    This variable sets up a path from which the build system can
                    locate recipes.
                    Here is the typical use:
                    <literallayout class='monospaced'>
     BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
                 ${LAYERDIR}/recipes-*/*/*.bbappend"
                    </literallayout>
                    Consequently, you need to be sure you locate your new recipe
                    inside your layer such that it can be found.</para>
                    <para>You can find more information on how layers are
                    structured in the
                    "<link linkend='understanding-and-creating-layers'>Understanding and Creating Layers</link>"
                    section.</para></listitem>
                <listitem><para><emphasis>Naming Your Recipe:</emphasis>
                    When you name your recipe, you need to follow this naming
                    convention:
                    <literallayout class='monospaced'>
     &lt;basename&gt;_&lt;version&gt;.bb
                    </literallayout>
                    Use lower-cased characters and do not include the reserved
                    suffixes <filename>-native</filename>,
                    <filename>-cross</filename>, <filename>-initial</filename>,
                    or <filename>-dev</filename> casually (i.e. do not use them
                    as part of your recipe name unless the string applies).
                    Here are some examples:
                    <literallayout class='monospaced'>
     cups_1.7.0.bb
     gawk_4.0.2.bb
     irssi_0.8.16-rc1.bb
                    </literallayout></para></listitem>
            </itemizedlist>
        </section>

        <section id='understanding-recipe-syntax'>
            <title>Understanding Recipe Syntax</title>

            <para>
                The basic items that make up a BitBake recipe file are
                as follows:
                <itemizedlist>
                    <listitem><para><emphasis>Variable Assignments and Manipulations:</emphasis>
                        Variable assignments allow a value to be assigned to a
                        variable.
                        The assignment can be static text or might include
                        the contents of other variables.
                        In addition to the assignment, appending and prepending
                        operations are also supported.</para>
                        <para>The following example shows some of the ways
                        you can use variables in recipes:
                        <literallayout class='monospaced'>
     S = "${WORKDIR}/postfix-${PV}"
     CFLAGS += "-DNO_ASM"
     SRC_URI_append = " file://fixup.patch"
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Functions:</emphasis>
                        Functions provide a series of actions to be performed.
                        You usually use functions to override the default
                        implementation of a task function or to compliment
                        a default function (i.e. append or prepend to an
                        existing function).
                        Standard functions use <filename>sh</filename> shell
                        syntax, although access to OpenEmbedded variables and
                        internal methods are also available.</para>
                        <para>The following is an example function from the
                        <filename>sed</filename> recipe:
                        <literallayout class='monospaced'>
     do_install () {
         autotools_do_install
         install -d ${D}${base_bindir}
         mv ${D}${bindir}/sed ${D}${base_bindir}/sed.${PN}
     }
                        </literallayout>
                        It is also possible to implement new functions that
                        are called between existing tasks as long as the
                        new functions are not replacing or complimenting the
                        default functions.
                        You can implement functions in Python
                        instead of shell.
                        Both of these options are not seen in the majority of
                        recipes.</para></listitem>
                    <listitem><para><emphasis>Keywords:</emphasis>
                        BitBake recipes use only a few keywords.
                        You use keywords to include common
                        functions (<filename>inherit</filename>), load parts
                        of a recipe from other files
                        (<filename>include</filename> and
                        <filename>require</filename>) and export variables
                        to the environment (<filename>export</filename>).</para>
                        <para>The following example shows the use of some of
                        these keywords:
                        <literallayout class='monospaced'>
     export POSTCONF = "${STAGING_BINDIR}/postconf"
     inherit autoconf
     require otherfile.inc
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Comments:</emphasis>
                        Any lines that begin with the hash character
                        (<filename>#</filename>) are treated as comment lines
                        and are ignored:
                        <literallayout class='monospaced'>
     # This is a comment
                        </literallayout>
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                This next list summarizes the most important and most commonly
                used parts of the recipe syntax.
                For more information on these parts of the syntax, you can
                reference the
                <ulink url='&YOCTO_DOCS_BB_URL;#bitbake-user-manual-metadata'>Syntax and Operators</ulink>
                chapter in the BitBake User Manual.
                <itemizedlist>
                    <listitem><para><emphasis>Line Continuation: <filename>\</filename></emphasis> -
                        Use the backward slash (<filename>\</filename>)
                        character to split a statement over multiple lines.
                        Place the slash character at the end of the line that
                        is to be continued on the next line:
                        <literallayout class='monospaced'>
     VAR = "A really long \
            line"
                        </literallayout>
                        <note>
                            You cannot have any characters including spaces
                            or tabs after the slash character.
                        </note>
                        </para></listitem>
                    <listitem><para><emphasis>Using Variables: <filename>{...}</filename></emphasis> -
                        Use the <filename>${&lt;varname&gt;}</filename> syntax to
                        access the contents of a variable:
                        <literallayout class='monospaced'>
     SRC_URI = "${SOURCEFORGE_MIRROR}/libpng/zlib-${PV}.tar.gz"
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Quote All Assignments: <filename>"&lt;value&gt;"</filename></emphasis> -
                        Use double quotes around the value in all variable
                        assignments.
                        <literallayout class='monospaced'>
     VAR1 = "${OTHERVAR}"
     VAR2 = "The version is ${PV}"
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Conditional Assignment: <filename>?=</filename></emphasis> -
                        Conditional assignment is used to assign a value to
                        a variable, but only when the variable is currently
                        unset.
                        Use the question mark followed by the equal sign
                        (<filename>?=</filename>) to make a "soft" assignment
                        used for conditional assignment.
                        Typically, "soft" assignments are used in the
                        <filename>local.conf</filename> file for variables
                        that are allowed to come through from the external
                        environment.
                        Doing so allows you to actually set variables from
                        the external environment that would otherwise be
                        overwritten.</para>
                        <para>Here is an example:
                        <literallayout class='monospaced'>
     VAR1 ?= "New value"
                        </literallayout>
                        In the previous example, <filename>VAR1</filename> is
                        set to "New value" if it is currently empty.
                        However, if <filename>VAR1</filename> has already been
                        set, it remains unchanged.</para>
                        <para>In this next example, <filename>VAR1</filename>
                        is left with the value "Original value":
                        <literallayout class='monospaced'>
     VAR1 = "Original value"
     VAR1 ?= "New value"
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Appending: <filename>+=</filename></emphasis> -
                        Use the plus character followed by the equals sign
                        (<filename>+=</filename>) to append values to existing
                        variables.
                        <note>
                            This operator adds a space between the existing
                            content of the variable and the new content.
                        </note></para>
                        <para>Here is an example:
                        <literallayout class='monospaced'>
     SRC_URI += "file://fix-makefile.patch"
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Prepending: <filename>=+</filename></emphasis> -
                        Use the equals sign followed by the plus character
                        (<filename>=+</filename>) to prepend values to existing
                        variables.
                        <note>
                            This operator adds a space between the new content
                            and the existing content of the variable.
                        </note></para>
                        <para>Here is an example:
                        <literallayout class='monospaced'>
     VAR =+ "Starts"
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Appending: <filename>_append</filename></emphasis> -
                        Use the <filename>_append</filename> operator to
                        append values to existing variables.
                        This operator does not add any additional space.
                        Also, the operator is applied after all the
                        <filename>+=</filename>, and
                        <filename>=+</filename> operators have been applied and
                        after all <filename>=</filename> assignments have
                        occurred.
                        </para>
                        <para>The following example shows the space being
                        explicitly added to the start to ensure the appended
                        value is not merged with the existing value:
                        <literallayout class='monospaced'>
     SRC_URI_append = " file://fix-makefile.patch"
                        </literallayout>
                        You can also use the <filename>_append</filename>
                        operator with overrides, which results in the actions
                        only being performed for the specified target or
                        machine:
                        <literallayout class='monospaced'>
     SRC_URI_append_sh4 = " file://fix-makefile.patch"
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Prepending: <filename>_prepend</filename></emphasis> -
                        Use the <filename>_prepend</filename> operator to
                        prepend values to existing variables.
                        This operator does not add any additional space.
                        This operator does not add any additional space.
                        Also, the operator is applied after all the
                        <filename>+=</filename>, and
                        <filename>=+</filename> operators have been applied and
                        after all <filename>=</filename> assignments have
                        occurred.
                        </para>
                        <para>The following example shows the space being
                        explicitly added to the end to ensure the prepended
                        value is not merged with the existing value:
                        <literallayout class='monospaced'>
     CFLAGS_prepend = "-I${S}/myincludes "
                        </literallayout>
                        You can also use the <filename>_prepend</filename>
                        operator with overrides, which results in the actions
                        only being performed for the specified target or
                        machine:
                        <literallayout class='monospaced'>
     CFLAGS_prepend_sh4 = " file://fix-makefile.patch"
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Indentation:</emphasis>
                        Use spaces for indentation rather than than tabs.
                        For shell functions, both currently work.
                        However, it is a policy decision of the Yocto Project
                        to use tabs in shell functions.
                        Realize that some layers have a policy to use spaces
                        for all indentation.
                        </para></listitem>
                    <listitem><para><emphasis>Using Python for Complex Operations: <filename>${@&lt;variable&gt;}</filename></emphasis> -
                        For more advanced processing, it is possible to use
                        Python code during variable assignments (e.g.
                        search and replacement on a variable).</para>
                        <para>You indicate Python code using the
                        <filename>${@&lt;variable&gt;}</filename> syntax for the
                        variable assignment:
                        <literallayout class='monospaced'>
     SRC_URI = "ftp://ftp.info-zip.org/pub/infozip/src/zip${@d.getVar('PV',1).replace('.', '')}.tgz
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Shell Function Syntax:</emphasis>
                        Use shell function syntax as if you were writing a shell
                        script when you describe a list of actions to take.
                        You should ensure that your script works with a generic
                        <filename>sh</filename> and that it does not require
                        any <filename>bash</filename> or other shell-specific
                        functionality.
                        The same considerations apply to various system
                        utilities (e.g. <filename>sed</filename>,
                        <filename>grep</filename>, <filename>awk</filename>,
                        and so forth) that you might wish to use.
                        If in doubt, you should check with multiple
                        implementations - including those from BusyBox.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='new-recipe-running-a-build-on-the-recipe'>
            <title>Running a Build on the Recipe</title>

            <para>
                Creating a new recipe is usually an iterative process that
                requires using BitBake to process the recipe multiple times in
                order to progressively discover and add information to the
                recipe.
            </para>

            <para>
                Assuming you have sourced a build environment setup script (i.e.
                <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>
                or
                <ulink url='&YOCTO_DOCS_REF_URL;#structure-memres-core-script'><filename>oe-init-build-env-memres</filename></ulink>)
                and you are in the
                <link linkend='build-directory'>Build Directory</link>,
                use BitBake to process your recipe.
                All you need to provide is the
                <filename>&lt;basename&gt;</filename> of the recipe as described
                in the previous section:
                <literallayout class='monospaced'>
     $ bitbake &lt;basename&gt;
                </literallayout>

            </para>

            <para>
                During the build, the OpenEmbedded build system creates a
                temporary work directory for the recipe
                (<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink><filename>}</filename>)
                where it keeps extracted source files, log files, intermediate
                compilation and packaging files, and so forth.
            </para>

            <para>
                The temporary work directory is constructed as follows and
                depends on several factors:
                <literallayout class='monospaced'>
     ${TMPDIR}/work/${MULTIMACH_TARGET_SYS}/${PN}/${EXTENDPE}${PV}-${PR}
                </literallayout>
                As an example, assume a Source Directory top-level folder named
                <filename>poky</filename>, a default Build Directory at
                <filename>poky/build</filename>, and a
                <filename>qemux86-poky-linux</filename> machine target system.
                Furthermore, suppose your recipe is named
                <filename>foo_1.3.0-r0.bb</filename>.
                In this case, the work directory the build system uses to
                build the package would be as follows:
                <literallayout class='monospaced'>
     poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0
                </literallayout>
                Inside this directory you can find sub-directories such as
                <filename>image</filename>, <filename>packages-split</filename>,
                and <filename>temp</filename>.
                After the build, you can examine these to determine how well
                the build went.
                <note>
                    You can find log files for each task in the recipe's
                    <filename>temp</filename> directory (e.g.
                    <filename>poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0/temp</filename>).
                    Log files are named <filename>log.&lt;taskname&gt;</filename>
                    (e.g. <filename>log.do_configure</filename>,
                    <filename>log.do_fetch</filename>, and
                    <filename>log.do_compile</filename>).
                </note>
            </para>

            <para>
                You can find more information about the build process in the
                "<ulink url='&YOCTO_DOCS_REF_URL;#closer-look'>A Closer Look at the Yocto Project Development Environment</ulink>"
                chapter of the Yocto Project Reference Manual.
            </para>

            <para>
                You can also reference the following variables in the
                Yocto Project Reference Manual's glossary for more information:
                <itemizedlist>
                    <listitem><ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>:
                        The top-level build output directory</listitem>
                    <listitem><ulink url='&YOCTO_DOCS_REF_URL;#var-MULTIMACH_TARGET_SYS'><filename>MULTIMACH_TARGET_SYS</filename></ulink>:
                        The target system identifier</listitem>
                    <listitem><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink>:
                        The recipe name</listitem>
                    <listitem><ulink url='&YOCTO_DOCS_REF_URL;#var-EXTENDPE'><filename>EXTENDPE</filename></ulink>:
                        The epoch - (if
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PE'><filename>PE</filename></ulink>
                        is not specified, which is usually the case for most
                        recipes, then <filename>EXTENDPE</filename> is blank)</listitem>
                    <listitem><ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>:
                        The recipe version</listitem>
                    <listitem><ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>:
                        The recipe revision</listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='new-recipe-fetching-code'>
            <title>Fetching Code</title>

            <para>
                The first thing your recipe must do is specify how to fetch
                the source files.
                Fetching is controlled mainly through the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                variable.
                Your recipe must have a <filename>SRC_URI</filename> variable
                that points to where the source is located.
                For a graphical representation of source locations, see the
                "<ulink url='&YOCTO_DOCS_REF_URL;#sources-dev-environment'>Sources</ulink>"
                section in the Yocto Project Reference Manual.
            </para>

            <para>
                The
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-fetch'><filename>do_fetch</filename></ulink>
                task uses the prefix of each entry in the
                <filename>SRC_URI</filename> variable value to determine what
                fetcher to use to get your source files.
                It is the <filename>SRC_URI</filename> variable that triggers
                the fetcher.
                The
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-patch'><filename>do_patch</filename></ulink>
                task uses the variable after source is fetched to apply
                patches.
                The OpenEmbedded build system uses
                <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESOVERRIDES'><filename>FILESOVERRIDES</filename></ulink>
                for scanning directory locations for local files in
                <filename>SRC_URI</filename>.
            </para>

            <para>
                The <filename>SRC_URI</filename> variable in your recipe must
                define each unique location for your source files.
                It is good practice to not hard-code pathnames in an URL used
                in <filename>SRC_URI</filename>.
                Rather than hard-code these paths, use
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink><filename>}</filename>,
                which causes the fetch process to use the version specified in
                the recipe filename.
                Specifying the version in this manner means that upgrading the
                recipe to a future version is as simple as renaming the recipe
                to match the new version.
            </para>

            <para>
                Here is a simple example from the
                <filename>meta/recipes-devtools/cdrtools/cdrtools-native_3.01a17.bb</filename>
                recipe where the source comes from a single tarball.
                Notice the use of the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
                variable:
                <literallayout class='monospaced'>
     SRC_URI = "ftp://ftp.berlios.de/pub/cdrecord/alpha/cdrtools-${PV}.tar.bz2"
                </literallayout>
            </para>

            <para>
                Files mentioned in <filename>SRC_URI</filename> whose names end
                in a typical archive extension (e.g. <filename>.tar</filename>,
                <filename>.tar.gz</filename>, <filename>.tar.bz2</filename>,
                <filename>.zip</filename>, and so forth), are automatically
                extracted during the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-unpack'><filename>do_unpack</filename></ulink>
                task.
                For another example that specifies these types of files, see
                the
                "<link linkend='new-recipe-autotooled-package'>Autotooled Package</link>"
                section.
            </para>

            <para>
                Another way of specifying source is from an SCM.
                For Git repositories, you must specify
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRCREV'><filename>SRCREV</filename></ulink>
                and you should specify
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
                to include the revision with
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRCPV'><filename>SRCPV</filename></ulink>.
                Here is an example from the recipe
                <filename>meta/recipes-kernel/blktrace/blktrace_git.bb</filename>:
                <literallayout class='monospaced'>
     SRCREV = "d6918c8832793b4205ed3bfede78c2f915c23385"

     PR = "r6"
     PV = "1.0.5+git${SRCPV}"

     SRC_URI = "git://git.kernel.dk/blktrace.git \
                file://ldflags.patch"
                </literallayout>
            </para>

            <para>
                If your <filename>SRC_URI</filename> statement includes
                URLs pointing to individual files fetched from a remote server
                other than a version control system, BitBake attempts to
                verify the files against checksums defined in your recipe to
                ensure they have not been tampered with or otherwise modified
                since the recipe was written.
                Two checksums are used:
                <filename>SRC_URI[md5sum]</filename> and
                <filename>SRC_URI[sha256sum]</filename>.
            </para>

            <para>
                If your <filename>SRC_URI</filename> variable points to
                more than a single URL (excluding SCM URLs), you need to
                provide the <filename>md5</filename> and
                <filename>sha256</filename> checksums for each URL.
                For these cases, you provide a name for each URL as part of
                the <filename>SRC_URI</filename> and then reference that name
                in the subsequent checksum statements.
                Here is an example:
                <literallayout class='monospaced'>
     SRC_URI = "${DEBIAN_MIRROR}/main/a/apmd/apmd_3.2.2.orig.tar.gz;name=tarball \
                ${DEBIAN_MIRROR}/main/a/apmd/apmd_${PV}.diff.gz;name=patch

     SRC_URI[tarball.md5sum] = "b1e6309e8331e0f4e6efd311c2d97fa8"
     SRC_URI[tarball.sha256sum] = "7f7d9f60b7766b852881d40b8ff91d8e39fccb0d1d913102a5c75a2dbb52332d"

     SRC_URI[patch.md5sum] = "57e1b689264ea80f78353519eece0c92"
     SRC_URI[patch.sha256sum] = "7905ff96be93d725544d0040e425c42f9c05580db3c272f11cff75b9aa89d430"
                </literallayout>
            </para>

            <para>
                To find these checksums, you can comment the statements out
                and then attempt to build the software.
                The build will produce an error for each missing checksum
                and as part of the error message provide the correct checksum
                string.
                Once you have the correct checksums, simply copy them into your
                recipe for a subsequent build.
            </para>

            <para>
                This final example is a bit more complicated and is from the
                <filename>meta/recipes-sato/rxvt-unicode/rxvt-unicode_9.19.bb</filename>
                recipe.
                The example's <filename>SRC_URI</filename> statement identifies
                multiple files as the source files for the recipe: a tarball, a
                patch file, a desktop file, and an icon.
                <literallayout class='monospaced'>
     SRC_URI = "http://dist.schmorp.de/rxvt-unicode/Attic/rxvt-unicode-${PV}.tar.bz2 \
                file://xwc.patch \
                file://rxvt.desktop \
                file://rxvt.png"
                </literallayout>
            </para>

            <para>
                When you specify local files using the
                <filename>file://</filename> URI protocol, the build system
                fetches files from the local machine.
                The path is relative to the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink>
                variable and searches specific directories in a certain order:
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BPN'><filename>BPN</filename></ulink><filename>}</filename>,
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BP'><filename>BP</filename></ulink><filename>}</filename>,
                and <filename>files</filename>.
                The directories are assumed to be subdirectories of the
                directory in which the recipe or append file resides.
                For another example that specifies these types of files, see the
                "<link linkend='new-recipe-single-c-file-package-hello-world'>Single .c File Package (Hello World!)</link>"
                section.
            </para>

            <para>
                The previous example also specifies a patch file.
                Patch files are files whose names end in
                <filename>.patch</filename> or <filename>.diff</filename>.
                The build system automatically applies patches as described
                in the
                "<link linkend='new-recipe-patching-code'>Patching Code</link>" section.
            </para>
        </section>

        <section id='new-recipe-unpacking-code'>
            <title>Unpacking Code</title>

            <para>
                During the build, the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-unpack'><filename>do_unpack</filename></ulink>
                task unpacks the source with
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink><filename>}</filename>
                pointing to where it is unpacked.
            </para>

            <para>
                If you are fetching your source files from an upstream source
                archived tarball and the tarball's internal structure matches
                the common convention of a top-level subdirectory named
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BPN'><filename>BPN</filename></ulink><filename>}-${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink><filename>}</filename>,
                then you do not need to set <filename>S</filename>.
                However, if <filename>SRC_URI</filename> specifies to fetch
                source from an archive that does not use this convention,
                or from an SCM like Git or Subversion, your recipe needs to
                define <filename>S</filename>.
            </para>

            <para>
                If processing your recipe using BitBake successfully unpacks
                the source files, you need to be sure that the directory
                pointed to by <filename>${S}</filename> matches the structure
                of the source.
            </para>
        </section>

        <section id='new-recipe-patching-code'>
            <title>Patching Code</title>

            <para>
                Sometimes it is necessary to patch code after it has been
                fetched.
                Any files mentioned in <filename>SRC_URI</filename> whose
                names end in <filename>.patch</filename> or
                <filename>.diff</filename> are treated as patches.
                The
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-patch'><filename>do_patch</filename></ulink>
                task automatically applies these patches.
            </para>

            <para>
                The build system should be able to apply patches with the "-p1"
                option (i.e. one directory level in the path will be stripped
                off).
                If your patch needs to have more directory levels stripped off,
                specify the number of levels using the "striplevel" option in
                the <filename>SRC_URI</filename> entry for the patch.
                Alternatively, if your patch needs to be applied in a specific
                subdirectory that is not specified in the patch file, use the
                "patchdir" option in the entry.
            </para>
        </section>

        <section id='new-recipe-licensing'>
            <title>Licensing</title>

            <para>
                Your recipe needs to have both the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE'><filename>LICENSE</filename></ulink>
                and
                <ulink url='&YOCTO_DOCS_REF_URL;#var-LIC_FILES_CHKSUM'><filename>LIC_FILES_CHKSUM</filename></ulink>
                variables:
                <itemizedlist>
                    <listitem><para><emphasis><filename>LICENSE</filename>:</emphasis>
                        This variable specifies the license for the software.
                        If you do not know the license under which the software
                        you are building is distributed, you should go to the
                        source code and look for that information.
                        Typical files containing this information include
                        <filename>COPYING</filename>,
                        <filename>LICENSE</filename>, and
                        <filename>README</filename> files.
                        You could also find the information near the top of
                        a source file.
                        For example, given a piece of software licensed under
                        the GNU General Public License version 2, you would
                        set <filename>LICENSE</filename> as follows:
                        <literallayout class='monospaced'>
     LICENSE = "GPLv2"
                        </literallayout></para>
                        <para>The licenses you specify within
                        <filename>LICENSE</filename> can have any name as long
                        as you do not use spaces, since spaces are used as
                        separators between license names.
                        For standard licenses, use the names of the files in
                        <filename>meta/files/common-licenses/</filename>
                        or the <filename>SPDXLICENSEMAP</filename> flag names
                        defined in <filename>meta/conf/licenses.conf</filename>.
                        </para></listitem>
                    <listitem><para><emphasis><filename>LIC_FILES_CHKSUM</filename>:</emphasis>
                        The OpenEmbedded build system uses this variable to
                        make sure the license text has not changed.
                        If it has, the build produces an error and it affords
                        you the chance to figure it out and correct the problem.
                        </para>
                        <para>You need to specify all applicable licensing
                        files for the software.
                        At the end of the configuration step, the build process
                        will compare the checksums of the files to be sure
                        the text has not changed.
                        Any differences result in an error with the message
                        containing the current checksum.
                        For more explanation and examples of how to set the
                        <filename>LIC_FILES_CHKSUM</filename> variable, see the
                        "<ulink url='&YOCTO_DOCS_REF_URL;#usingpoky-configuring-LIC_FILES_CHKSUM'>Tracking License Changes</ulink>"
                        section in the Yocto Project Reference Manual.</para>
                        <para>To determine the correct checksum string, you
                        can list the appropriate files in the
                        <filename>LIC_FILES_CHKSUM</filename> variable with
                        incorrect md5 strings, attempt to build the software,
                        and then note the resulting error messages that will
                        report the correct md5 strings.
                        Here is an example that assumes the software has a
                        <filename>COPYING</filename> file:
                        <literallayout class='monospaced'>
     LIC_FILES_CHKSUM = "file://COPYING;md5=xxx"
                        </literallayout>
                        When you try to build the software, the build system
                        will produce an error and give you the correct string
                        that you can substitute into the recipe file for a
                        subsequent build.
                        </para></listitem>
                </itemizedlist>
            </para>

<!--

            <para>
                For trying this out I created a new recipe named
                <filename>htop_1.0.2.bb</filename> and put it in
                <filename>poky/meta/recipes-extended/htop</filename>.
                There are two license type statements in my very simple
                recipe:
                <literallayout class='monospaced'>
     LICENSE = ""

     LIC_FILES_CHKSUM = ""

     SRC_URI[md5sum] = ""
     SRC_URI[sha256sum] = ""
                </literallayout>
                Evidently, you need to run a <filename>bitbake -c cleanall htop</filename>.
                Next, you delete or comment out the two <filename>SRC_URI</filename>
                lines at the end and then attempt to build the software with
                <filename>bitbake htop</filename>.
                Doing so causes BitBake to report some errors and and give
                you the actual strings you need for the last two
                <filename>SRC_URI</filename> lines.
                Prior to this, you have to dig around in the home page of the
                source for <filename>htop</filename> and determine that the
                software is released under GPLv2.
                You can provide that in the <filename>LICENSE</filename>
                statement.
                Now you edit your recipe to have those two strings for
                the <filename>SRC_URI</filename> statements:
                <literallayout class='monospaced'>
     LICENSE = "GPLv2"

     LIC_FILES_CHKSUM = ""

     SRC_URI = "${SOURCEFORGE_MIRROR}/htop/htop-${PV}.tar.gz"
     SRC_URI[md5sum] = "0d01cca8df3349c74569cefebbd9919e"
     SRC_URI[sha256sum] = "ee60657b044ece0df096c053060df7abf3cce3a568ab34d260049e6a37ccd8a1"
                </literallayout>
                At this point, you can build the software again using the
                <filename>bitbake htop</filename> command.
                There is just a set of errors now associated with the
                empty <filename>LIC_FILES_CHKSUM</filename> variable now.
            </para>
-->

        </section>

        <section id='new-recipe-configuring-the-recipe'>
            <title>Configuring the Recipe</title>

            <para>
                Most software provides some means of setting build-time
                configuration options before compilation.
                Typically, setting these options is accomplished by running a
                configure script with some options, or by modifying a build
                configuration file.
            </para>

            <para>
                A major part of build-time configuration is about checking for
                build-time dependencies and possibly enabling optional
                functionality as a result.
                You need to specify any build-time dependencies for the
                software you are building in your recipe's
                <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
                value, in terms of other recipes that satisfy those
                dependencies.
                You can often find build-time or runtime
                dependencies described in the software's documentation.
            </para>

            <para>
                The following list provides configuration items of note based
                on how your software is built:
                <itemizedlist>
                    <listitem><para><emphasis>Autotools:</emphasis>
                        If your source files have a
                        <filename>configure.ac</filename> file, then your
                        software is built using Autotools.
                        If this is the case, you just need to worry about
                        tweaking the configuration.</para>
                        <para>When using Autotools, your recipe needs to inherit
                        the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-autotools'><filename>autotools</filename></ulink>
                        class and your recipe does not have to contain a
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-configure'><filename>do_configure</filename></ulink>
                        task.
                        However, you might still want to make some adjustments.
                        For example, you can set
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OECONF'><filename>EXTRA_OECONF</filename></ulink>
                        to pass any needed configure options that are specific
                        to the recipe.</para></listitem>
                    <listitem><para><emphasis>CMake:</emphasis>
                        If your source files have a
                        <filename>CMakeLists.txt</filename> file, then your
                        software is built using CMake.
                        If this is the case, you just need to worry about
                        tweaking the configuration.</para>
                        <para>When you use CMake, your recipe needs to inherit
                        the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-cmake'><filename>cmake</filename></ulink>
                        class and your recipe does not have to contain a
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-configure'><filename>do_configure</filename></ulink>
                        task.
                        You can make some adjustments by setting
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OECMAKE'><filename>EXTRA_OECMAKE</filename></ulink>
                        to pass any needed configure options that are specific
                        to the recipe.</para></listitem>
                    <listitem><para><emphasis>Other:</emphasis>
                        If your source files do not have a
                        <filename>configure.ac</filename> or
                        <filename>CMakeLists.txt</filename> file, then your
                        software is built using some method other than Autotools
                        or CMake.
                        If this is the case, you normally need to provide a
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-configure'><filename>do_configure</filename></ulink>
                        task in your recipe
                        unless, of course, there is nothing to configure.
                        </para>
                        <para>Even if your software is not being built by
                        Autotools or CMake, you still might not need to deal
                        with any configuration issues.
                        You need to determine if configuration is even a required step.
                        You might need to modify a Makefile or some configuration file
                        used for the build to specify necessary build options.
                        Or, perhaps you might need to run a provided, custom
                        configure script with the appropriate options.</para>
                        <para>For the case involving a custom configure
                        script, you would run
                        <filename>./configure --help</filename> and look for
                        the options you need to set.</para></listitem>
                </itemizedlist>
            </para>

            <para>
                Once configuration succeeds, it is always good practice to
                look at the <filename>log.do_configure</filename> file to
                ensure that the appropriate options have been enabled and no
                additional build-time dependencies need to be added to
                <filename>DEPENDS</filename>.
                For example, if the configure script reports that it found
                something not mentioned in <filename>DEPENDS</filename>, or
                that it did not find something that it needed for some
                desired optional functionality, then you would need to add
                those to <filename>DEPENDS</filename>.
                Looking at the log might also reveal items being checked for
                and/or enabled that you do not want, or items not being found
                that are in <filename>DEPENDS</filename>, in which case
                you would need to look at passing extra options to the
                configure script as needed.
                For reference information on configure options specific to the
                software you are building, you can consult the output of the
                <filename>./configure --help</filename> command within
                <filename>${S}</filename> or consult the software's upstream
                documentation.
            </para>
        </section>

        <section id='new-recipe-compilation'>
            <title>Compilation</title>

            <para>
                During a build, the <filename>do_compile</filename> task
                happens after source is fetched, unpacked, and configured.
                If the recipe passes through <filename>do_compile</filename>
                successfully, nothing needs to be done.
            </para>

            <para>
                However, if the compile step fails, you need to diagnose the
                failure.
                Here are some common issues that cause failures:
                <itemizedlist>
                    <listitem><para><emphasis>Parallel build failures:</emphasis>
                        These failures manifest themselves as intermittent
                        errors, or errors reporting that a file or directory
                        that should be created by some other part of the build
                        process could not be found.
                        This type of failure can occur even if, upon inspection,
                        the file or directory does exist after the build has
                        failed, because that part of the build process happened
                        in the wrong order.</para>
                        <para>To fix the problem, you need to either satisfy
                        the missing dependency in the Makefile or whatever
                        script produced the Makefile, or (as a workaround)
                        set
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PARALLEL_MAKE'><filename>PARALLEL_MAKE</filename></ulink>
                        to an empty string:
                        <literallayout class='monospaced'>
     PARALLEL_MAKE = ""
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Improper host path usage:</emphasis>
                        This failure applies to recipes building for the target
                        or <filename>nativesdk</filename> only.
                        The failure occurs when the compilation process uses
                        improper headers, libraries, or other files from the
                        host system when cross-compiling for the target.
                        </para>
                        <para>To fix the problem, examine the
                        <filename>log.do_compile</filename> file to identify
                        the host paths being used (e.g.
                        <filename>/usr/include</filename>,
                        <filename>/usr/lib</filename>, and so forth) and then
                        either add configure options, apply a patch, or do both.
                        </para></listitem>
                    <listitem><para><emphasis>Failure to find required
                        libraries/headers:</emphasis>
                        If a build-time dependency is missing because it has
                        not been declared in
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>,
                        or because the dependency exists but the path used by
                        the build process to find the file is incorrect and the
                        configure step did not detect it, the compilation
                        process could fail.
                        For either of these failures, the compilation process
                        notes that files could not be found.
                        In these cases, you need to go back and add additional
                        options to the configure script as well as possibly
                        add additional build-time dependencies to
                        <filename>DEPENDS</filename>.
                        Occasionally, it is necessary to apply a patch to the
                        source to ensure the correct paths are used.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='new-recipe-installing'>
            <title>Installing</title>

            <para>
                During <filename>do_install</filename>, the task copies the
                built files along with their hierarchy to locations that
                would mirror their locations on the target device.
                The installation process copies files from the
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink><filename>}</filename>,
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-B'><filename>B</filename></ulink><filename>}</filename>,
                and
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink><filename>}</filename>
                directories to the
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink><filename>}</filename>
                directory to create the structure as it should appear on the
                target system.
            </para>

            <para>
                How your software is built affects what you must do to be
                sure your software is installed correctly.
                The following list describes what you must do for installation
                depending on the type of build system used by the software
                being built:
                <itemizedlist>
                    <listitem><para><emphasis>Autotools and CMake:</emphasis>
                        If the software your recipe is building uses Autotools
                        or CMake, the OpenEmbedded build
                        system understands how to install the software.
                        Consequently, you do not have to have a
                        <filename>do_install</filename> task as part of your
                        recipe.
                        You just need to make sure the install portion of the
                        build completes with no issues.
                        However, if you wish to install additional files not
                        already being installed by
                        <filename>make install</filename>, you should do this
                        using a <filename>do_install_append</filename> function
                        using the install command as described in
                        <emphasis>Manual</emphasis> later in this list.
                        </para></listitem>
                    <listitem><para><emphasis>Other (using
                        <filename>make install</filename>):</emphasis>
                        You need to define a
                        <filename>do_install</filename> function in your
                        recipe.
                        The function should call
                        <filename>oe_runmake install</filename> and will likely
                        need to pass in the destination directory as well.
                        How you pass that path is dependent on how the
                        <filename>Makefile</filename> being run is written
                        (e.g. <filename>DESTDIR=${D}</filename>,
                        <filename>PREFIX=${D}</filename>,
                        <filename>INSTALLROOT=${D}</filename>, and so forth).
                        </para>
                        <para>For an example recipe using
                        <filename>make install</filename>, see the
                        "<link linkend='new-recipe-makefile-based-package'>Makefile-Based Package</link>"
                        section.</para></listitem>
                    <listitem><para><emphasis>Manual:</emphasis>
                        You need to define a
                        <filename>do_install</filename> function in your
                        recipe.
                        The function must first use
                        <filename>install -d</filename> to create the
                        directories.
                        Once the directories exist, your function can use
                        <filename>install</filename> to manually install the
                        built software into the directories.</para>
                        <para>You can find more information on
                        <filename>install</filename> at
                        <ulink url='http://www.gnu.org/software/coreutils/manual/html_node/install-invocation.html'></ulink>.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                For the scenarios that do not use Autotools or
                CMake, you need to track the installation
                and diagnose and fix any issues until everything installs
                correctly.
                You need to look in the default location of
                <filename>${D}</filename>, which is
                <filename>${WORKDIR}/image</filename>, to be sure your
                files have been installed correctly.
            </para>

            <note>
                During the installation process, you might need to modify
                some of the installed files to suit the target layout.
                For example, you might need to replace hard-coded paths in an
                initscript with values of variables provided by the build
                system, such as replacing <filename>/usr/bin/</filename> with
                <filename>${bindir}</filename>.
                If you do perform such modifications during
                <filename>do_install</filename>, be sure to modify the
                destination file after copying rather than before copying.
                Modifying after copying ensures that the build system can
                re-execute <filename>do_install</filename> if needed.
            </note>

            <note>
                <filename>oe_runmake install</filename>, which can be run
                directly or can be run indirectly by the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-autotools'><filename>autotools</filename></ulink>
                and
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-cmake'><filename>cmake</filename></ulink>
                classes, runs <filename>make install</filename> in parallel.
                Sometimes, a Makefile can have missing dependencies between
                targets that can result in race conditions.
                If you experience intermittent failures during
                <filename>do_install</filename>, you might be able to work
                around them by disabling parallel Makefile installs
                by adding the following to the recipe:
                <literallayout class='monospaced'>
     PARALLEL_MAKEINST = ""
                </literallayout>
                See
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PARALLEL_MAKEINST'><filename>PARALLEL_MAKEINST</filename></ulink>
                for additional information.
            </note>
        </section>

        <section id='new-recipe-enabling-system-services'>
            <title>Enabling System Services</title>

            <para>
                If you want to install a service, which is a process that
                usually starts on boot and runs in the background, then
                you must include some additional definitions in your recipe.
            </para>

            <para>
                If you are adding services and the service initialization
                script or the service file itself is not installed, you must
                provide for that installation in your recipe using a
                <filename>do_install_append</filename> function.
                If your recipe already has a <filename>do_install</filename>
                function, update the function near its end rather than
                adding an additional <filename>do_install_append</filename>
                function.
            </para>

            <para>
                When you create the installation for your services, you need
                to accomplish what is normally done by
                <filename>make install</filename>.
                In other words, make sure your installation arranges the output
                similar to how it is arranged on the target system.
            </para>

            <para>
                The OpenEmbedded build system provides support for starting
                services two different ways:
                <itemizedlist>
                    <listitem><para><emphasis>SysVinit:</emphasis>
                        SysVinit is a system and service manager that
                        manages the init system used to control the very basic
                        functions of your system.
                        The init program is the first program
                        started by the Linux kernel when the system boots.
                        Init then controls the startup, running and shutdown
                        of all other programs.</para>
                        <para>To enable a service using SysVinit, your recipe
                        needs to inherit the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-update-rc.d'><filename>update-rc.d</filename></ulink>
                        class.
                        The class helps facilitate safely installing the
                        package on the target.</para>
                        <para>You will need to set the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-INITSCRIPT_PACKAGES'><filename>INITSCRIPT_PACKAGES</filename></ulink>,
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-INITSCRIPT_NAME'><filename>INITSCRIPT_NAME</filename></ulink>,
                        and
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-INITSCRIPT_PARAMS'><filename>INITSCRIPT_PARAMS</filename></ulink>
                        variables within your recipe.</para></listitem>
                    <listitem><para><emphasis>systemd:</emphasis>
                        System Management Daemon (systemd) was designed to
                        replace SysVinit and to provide
                        enhanced management of services.
                        For more information on systemd, see the systemd
                        homepage at
                        <ulink url='http://freedesktop.org/wiki/Software/systemd/'></ulink>.
                        </para>
                        <para>To enable a service using systemd, your recipe
                        needs to inherit the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-systemd'><filename>systemd</filename></ulink>
                        class.
                        See the <filename>systemd.class</filename> file
                        located in your
                        <link linkend='source-directory'>Source Directory</link>.
                        section for more information.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='new-recipe-packaging'>
            <title>Packaging</title>

            <para>
                The <filename>do_package</filename> task splits the files
                produced by the recipe into logical components.
                Even software that produces a single binary might still have
                debug symbols, documentation, and other logical components
                that should be split out.
                The <filename>do_package</filename> task ensures that files
                are split up and packaged correctly.
            </para>

            <para>
                After you build your software, you need to be sure your packages
                are correct.
                Examine the
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink><filename>}/packages-split</filename>
                directory and make sure files are where you expect them to be.
            </para>

            <para>
                If you discover problems, you can set
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>,
                <ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES</filename></ulink>,
                <filename>do_install(_append)</filename>, and so forth as
                needed.
            </para>

            <para>
                See the
                "<link linkend='splitting-an-application-into-multiple-packages'>Splitting an Application into Multiple Packages</link>"
                section for an example that shows how you might split
                your software into more than one package.
            </para>

            <para>
                For an example showing how to install a post-installation
                script, see the
                "<link linkend='new-recipe-post-installation-scripts'>Post-Installation Scripts</link>"
                section.
            </para>
        </section>

        <section id='properly-versioning-pre-release-recipes'>
            <title>Properly Versioning Pre-Release Recipes</title>

            <para>
                Sometimes the name of a recipe can lead to versioning
                problems when the recipe is upgraded to a final release.
                For example, consider the
                <filename>irssi_0.8.16-rc1.bb</filename> recipe file in
                the list of example recipes in the
                "<link linkend='new-recipe-storing-and-naming-the-recipe'>Storing and Naming the Recipe</link>"
                section.
                This recipe is at a release candidate stage (i.e.
                "rc1").
                When the recipe is released, the recipe filename becomes
                <filename>irssi_0.8.16.bb</filename>.
                The version change from <filename>0.8.16-rc1</filename>
                to <filename>0.8.16</filename> is seen as a decrease by the
                build system and package managers, so the resulting packages
                will not correctly trigger an upgrade.
            </para>

            <para>
                In order to ensure the versions compare properly, the
                recommended convention is to set
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
                within the recipe to
                "&lt;previous version&gt;+&lt;current version&gt;".
                You can use an additional variable so that you can use the
                current version elsewhere.
                Here is an example:
                <literallayout class='monospaced'>
     REALPV = "0.8.16-rc1"
     PV = "0.8.15+${REALPV}"
                </literallayout>
            </para>
        </section>

        <section id='new-recipe-post-installation-scripts'>
            <title>Post-Installation Scripts</title>

            <para>
                Post-installation scripts run immediately after installing
                a package on the target, or during image creation when a
                package is included in an image.
                To add a post-installation script to a package, add a
                <filename>pkg_postinst_PACKAGENAME()</filename> function to
                the recipe file (<filename>.bb</filename>) and use
                <filename>PACKAGENAME</filename> as the name of the package
                you want to attach to the <filename>postinst</filename>
                script.
                To apply the post-installation script to the main package
                for the recipe, which is usually what is required, specify
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink><filename>}</filename>
                in place of <filename>PACKAGENAME</filename>.
            </para>

            <para>
                A post-installation function has the following structure:
                <literallayout class='monospaced'>
     pkg_postinst_PACKAGENAME () {
     #!/bin/sh -e
     # Commands to carry out
     }
                </literallayout>
            </para>

            <para>
                The script defined in the post-installation function is
                called when the root filesystem is created.
                If the script succeeds, the package is marked as installed.
                If the script fails, the package is marked as unpacked and
                the script is executed when the image boots again.
            </para>

            <para>
                Sometimes it is necessary for the execution of a
                post-installation script to be delayed until the first boot.
                For example, the script might need to be executed on the
                device itself.
                To delay script execution until boot time, use the following
                structure in the post-installation script:
                <literallayout class='monospaced'>
     pkg_postinst_PACKAGENAME () {
     #!/bin/sh -e
     if [ x"$D" = "x" ]; then
          # Actions to carry out on the device go here
     else
          exit 1
     fi
     }
                </literallayout>
            </para>

            <para>
                The previous example delays execution until the image boots
                again because the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-D'>D</ulink></filename>
                variable points to the directory containing the image when
                the root filesystem is created at build time but is unset
                when executed on the first boot.
            </para>

            <note>
                Equivalent support for pre-install, pre-uninstall, and
                post-uninstall scripts exist by way of
                <filename>pkg_preinst</filename>,
                <filename>pkg_prerm</filename>, and
                <filename>pkg_postrm</filename>, respectively.
                These scrips work in exactly the same way as does
                <filename>pkg_postinst</filename> with the exception that they
                run at different times.
                Also, because of when they run, they are not applicable to
                being run at image creation time like
                <filename>pkg_postinst</filename>.
            </note>
        </section>

        <section id='new-recipe-testing'>
            <title>Testing</title>

            <para>
                The final step for completing your recipe is to be sure that
                the software you built runs correctly.
                To accomplish runtime testing, add the build's output
                packages to your image and test them on the target.
            </para>

            <para>
                For information on how to customize your image by adding
                specific packages, see the
                "<link linkend='usingpoky-extend-customimage'>Customizing Images</link>"
                section.
            </para>
        </section>

        <section id='new-recipe-testing-examples'>
            <title>Examples</title>

            <para>
                To help summarize how to write a recipe, this section provides
                some examples given various scenarios:
                <itemizedlist>
                    <listitem><para>Recipes that use local files</para></listitem>
                    <listitem><para>Using an Autotooled package</para></listitem>
                    <listitem><para>Using a Makefile-based package</para></listitem>
                    <listitem><para>Splitting an application into multiple packages</para></listitem>
                </itemizedlist>
            </para>

            <section id='new-recipe-single-c-file-package-hello-world'>
                <title>Single .c File Package (Hello World!)</title>

                <para>
                    Building an application from a single file that is stored
                    locally (e.g. under <filename>files/</filename>) requires
                    a recipe that has the file listed in the
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>
                    variable.
                    Additionally, you need to manually write the
                    <filename>do_compile</filename> and
                    <filename>do_install</filename> tasks.
                    The <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'>S</ulink></filename>
                    variable defines the directory containing the source code,
                    which is set to
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>
                    in this case - the directory BitBake uses for the build.
                    <literallayout class='monospaced'>
     SUMMARY = "Simple helloworld application"
     SECTION = "examples"
     LICENSE = "MIT"
     LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/MIT;md5=0835ade698e0bcf8506ecda2f7b4f302"

     SRC_URI = "file://helloworld.c"

     S = "${WORKDIR}"

     do_compile() {
     	${CC} helloworld.c -o helloworld
     }

     do_install() {
     	install -d ${D}${bindir}
     	install -m 0755 helloworld ${D}${bindir}
     }
                    </literallayout>
                </para>

                <para>
                    By default, the <filename>helloworld</filename>,
                    <filename>helloworld-dbg</filename>, and
                    <filename>helloworld-dev</filename> packages are built.
                    For information on how to customize the packaging process,
                    see the
                    "<link linkend='splitting-an-application-into-multiple-packages'>Splitting an Application into Multiple Packages</link>"
                    section.
                </para>
            </section>

            <section id='new-recipe-autotooled-package'>
                <title>Autotooled Package</title>
                <para>
                    Applications that use Autotools such as <filename>autoconf</filename> and
                    <filename>automake</filename> require a recipe that has a source archive listed in
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename> and
                    also inherit the
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-autotools'><filename>autotools</filename></ulink>
                    class, which contains the definitions of all the steps
                    needed to build an Autotool-based application.
                    The result of the build is automatically packaged.
                    And, if the application uses NLS for localization, packages with local information are
                    generated (one package per language).
                    Following is one example: (<filename>hello_2.3.bb</filename>)
                    <literallayout class='monospaced'>
     SUMMARY = "GNU Helloworld application"
     SECTION = "examples"
     LICENSE = "GPLv2+"
     LIC_FILES_CHKSUM = "file://COPYING;md5=751419260aa954499f7abaabaa882bbe"

     SRC_URI = "${GNU_MIRROR}/hello/hello-${PV}.tar.gz"

     inherit autotools gettext
                     </literallayout>
                </para>

                <para>
                    The variable
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LIC_FILES_CHKSUM'>LIC_FILES_CHKSUM</ulink></filename>
                    is used to track source license changes as described in the
                    "<ulink url='&YOCTO_DOCS_REF_URL;#usingpoky-configuring-LIC_FILES_CHKSUM'>Tracking License Changes</ulink>" section.
                    You can quickly create Autotool-based recipes in a manner similar to the previous example.
                </para>
            </section>

            <section id='new-recipe-makefile-based-package'>
                <title>Makefile-Based Package</title>

                <para>
                    Applications that use GNU <filename>make</filename> also require a recipe that has
                    the source archive listed in
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>.
                    You do not need to add a <filename>do_compile</filename> step since by default BitBake
                    starts the <filename>make</filename> command to compile the application.
                    If you need additional <filename>make</filename> options, you should store them in the
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OEMAKE'>EXTRA_OEMAKE</ulink></filename>
                    variable.
                    BitBake passes these options into the <filename>make</filename> GNU invocation.
                    Note that a <filename>do_install</filename> task is still required.
                    Otherwise, BitBake runs an empty <filename>do_install</filename> task by default.
                </para>

               <para>
                    Some applications might require extra parameters to be passed to the compiler.
                    For example, the application might need an additional header path.
                    You can accomplish this by adding to the
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-CFLAGS'>CFLAGS</ulink></filename> variable.
                    The following example shows this:
                    <literallayout class='monospaced'>
     CFLAGS_prepend = "-I ${S}/include "
                    </literallayout>
                </para>

                <para>
                In the following example, <filename>mtd-utils</filename> is a makefile-based package:
                    <literallayout class='monospaced'>
     SUMMARY = "Tools for managing memory technology devices."
     SECTION = "base"
     DEPENDS = "zlib lzo e2fsprogs util-linux"
     HOMEPAGE = "http://www.linux-mtd.infradead.org/"
     LICENSE = "GPLv2+"
     LIC_FILES_CHKSUM = "file://COPYING;md5=0636e73ff0215e8d672dc4c32c317bb3 \
                    file://include/common.h;beginline=1;endline=17;md5=ba05b07912a44ea2bf81ce409380049c"

     SRC_URI = "git://git.infradead.org/mtd-utils.git;protocol=git;tag=995cfe51b0a3cf32f381c140bf72b21bf91cef1b \
	     	file://add-exclusion-to-mkfs-jffs2-git-2.patch"

     S = "${WORKDIR}/git/"

     PR = "r1"

     EXTRA_OEMAKE = "'CC=${CC}' 'RANLIB=${RANLIB}' 'AR=${AR}' \
        'CFLAGS=${CFLAGS} -I${S}/include -DWITHOUT_XATTR' 'BUILDDIR=${S}'"

     do_install () {
	     oe_runmake install DESTDIR=${D} SBINDIR=${sbindir} MANDIR=${mandir} \
            INCLUDEDIR=${includedir}
	     install -d ${D}${includedir}/mtd/
	     for f in ${S}/include/mtd/*.h; do
	     	install -m 0644 $f ${D}${includedir}/mtd/
	     done
     }

     PARALLEL_MAKE = ""

     BBCLASSEXTEND = "native"
                    </literallayout>
                </para>
            </section>

            <section id='splitting-an-application-into-multiple-packages'>
                <title>Splitting an Application into Multiple Packages</title>

                <para>
                    You can use the variables
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'>PACKAGES</ulink></filename> and
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'>FILES</ulink></filename>
                    to split an application into multiple packages.
                </para>

                <para>
                    Following is an example that uses the <filename>libxpm</filename> recipe.
                    By default, this recipe generates a single package that contains the library along
                    with a few binaries.
                    You can modify the recipe to split the binaries into separate packages:
                    <literallayout class='monospaced'>
     require xorg-lib-common.inc

     SUMMARY = "X11 Pixmap library"
     LICENSE = "X-BSD"
     LIC_FILES_CHKSUM = "file://COPYING;md5=3e07763d16963c3af12db271a31abaa5"
     DEPENDS += "libxext libsm libxt"
     PR = "r3"
     PE = "1"

     XORG_PN = "libXpm"

     PACKAGES =+ "sxpm cxpm"
     FILES_cxpm = "${bindir}/cxpm"
     FILES_sxpm = "${bindir}/sxpm"
                    </literallayout>
                </para>

                <para>
                    In the previous example, we want to ship the <filename>sxpm</filename>
                    and <filename>cxpm</filename> binaries in separate packages.
                    Since <filename>bindir</filename> would be packaged into the main
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'>PN</ulink></filename>
                    package by default, we prepend the <filename>PACKAGES</filename>
                    variable so additional package names are added to the start of list.
                    This results in the extra <filename>FILES_*</filename>
                    variables then containing information that define which files and
                    directories go into which packages.
                    Files included by earlier packages are skipped by latter packages.
                    Thus, the main <filename>PN</filename> package
                    does not include the above listed files.
                </para>
            </section>
        </section>
    </section>

    <section id="platdev-newmachine">
        <title>Adding a New Machine</title>

        <para>
            Adding a new machine to the Yocto Project is a straight forward
            process.
            This section describes how to add machines that are similar
            to those that the Yocto Project already supports.
            <note>
                Although well within the capabilities of the Yocto Project,
                adding a totally new architecture might require
                changes to <filename>gcc/eglibc</filename> and to the site
                information, which is beyond the scope of this manual.
            </note>
        </para>

        <para>
            For a complete example that shows how to add a new machine,
            see the
            "<ulink url='&YOCTO_DOCS_BSP_URL;#creating-a-new-bsp-layer-using-the-yocto-bsp-script'>Creating a New BSP Layer Using the yocto-bsp Script</ulink>"
            section in the Yocto Project Board Support Package (BSP) Developer's Guide.
        </para>

        <section id="platdev-newmachine-conffile">
            <title>Adding the Machine Configuration File</title>

            <para>
                To add a new machine, you need to add a new machine
                configuration file to the layer's
                <filename>conf/machine</filename> directory.
                This configuration file provides details about the device
                you are adding.
            </para>

            <para>
                The OpenEmbedded build system uses the root name of the
                machine configuration file to reference the new machine.
                For example, given a machine configuration file named
                <filename>crownbay.conf</filename>, the build system
                recognizes the machine as "crownbay".
            </para>

            <para>
                The most important variables you must set in your machine
                configuration file are as follows:
                <itemizedlist>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-TARGET_ARCH'>TARGET_ARCH</ulink></filename>
                        (e.g. "arm")</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PREFERRED_PROVIDER'>PREFERRED_PROVIDER</ulink>_virtual/kernel</filename>
                        (see below)</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_FEATURES'>MACHINE_FEATURES</ulink></filename>
                        (e.g. "apm screen wifi")</para></listitem>
                </itemizedlist>
            </para>

            <para>
                You might also need these variables:
                <itemizedlist>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SERIAL_CONSOLES'>SERIAL_CONSOLES</ulink></filename>
                        (e.g. "115200;ttyS0 115200;ttyS1")</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_IMAGETYPE'>KERNEL_IMAGETYPE</ulink></filename>
                        (e.g. "zImage")</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FSTYPES'>IMAGE_FSTYPES</ulink></filename>
                        (e.g. "tar.gz jffs2")</para></listitem>
                </itemizedlist>
            </para>

            <para>
                You can find full details on these variables in the reference
                section.
                You can leverage existing machine <filename>.conf</filename>
                files from <filename>meta-yocto-bsp/conf/machine/</filename>.
            </para>
        </section>

        <section id="platdev-newmachine-kernel">
            <title>Adding a Kernel for the Machine</title>

            <para>
                The OpenEmbedded build system needs to be able to build a kernel
                for the machine.
                You need to either create a new kernel recipe for this machine,
                or extend an existing kernel recipe.
                You can find several kernel recipe examples in the
                Source Directory at
                <filename>meta/recipes-kernel/linux</filename>
                that you can use as references.
            </para>

            <para>
                If you are creating a new kernel recipe, normal recipe-writing
                rules apply for setting up a
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>.
                Thus, you need to specify any necessary patches and set
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'>S</ulink></filename>
                to point at the source code.
                You need to create a <filename>do_configure</filename> task that
                configures the unpacked kernel with a
                <filename>defconfig</filename> file.
                You can do this by using a <filename>make defconfig</filename>
                command or, more commonly, by copying in a suitable
                <filename>defconfig</filename> file and then running
                <filename>make oldconfig</filename>.
                By making use of <filename>inherit kernel</filename> and
                potentially some of the <filename>linux-*.inc</filename> files,
                most other functionality is centralized and the defaults of the
                class normally work well.
            </para>

            <para>
                If you are extending an existing kernel recipe, it is usually
                a matter of adding a suitable <filename>defconfig</filename>
                file.
                The file needs to be added into a location similar to
                <filename>defconfig</filename> files used for other machines
                in a given kernel recipe.
                A possible way to do this is by listing the file in the
                <filename>SRC_URI</filename> and adding the machine to the
                expression in
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-COMPATIBLE_MACHINE'>COMPATIBLE_MACHINE</ulink></filename>:
                <literallayout class='monospaced'>
     COMPATIBLE_MACHINE = '(qemux86|qemumips)'
                </literallayout>
            </para>
        </section>

        <section id="platdev-newmachine-formfactor">
            <title>Adding a Formfactor Configuration File</title>

            <para>
                A formfactor configuration file provides information about the
                target hardware for which the image is being built and information that
                the build system cannot obtain from other sources such as the kernel.
                Some examples of information contained in a formfactor configuration file include
                framebuffer orientation, whether or not the system has a keyboard,
                the positioning of the keyboard in relation to the screen, and
                the screen resolution.
            </para>

            <para>
                The build system uses reasonable defaults in most cases.
                However, if customization is
                necessary, you need to create a <filename>machconfig</filename> file
                in the <filename>meta/recipes-bsp/formfactor/files</filename>
                directory.
                This directory contains directories for specific machines such as
                <filename>qemuarm</filename> and <filename>qemux86</filename>.
                For information about the settings available and the defaults, see the
                <filename>meta/recipes-bsp/formfactor/files/config</filename> file found in the
                same area.
            </para>

            <para>
                Following is an example for "qemuarm" machine:
                <literallayout class='monospaced'>
     HAVE_TOUCHSCREEN=1
     HAVE_KEYBOARD=1

     DISPLAY_CAN_ROTATE=0
     DISPLAY_ORIENTATION=0
     #DISPLAY_WIDTH_PIXELS=640
     #DISPLAY_HEIGHT_PIXELS=480
     #DISPLAY_BPP=16
     DISPLAY_DPI=150
     DISPLAY_SUBPIXEL_ORDER=vrgb
                </literallayout>
            </para>
        </section>
    </section>

    <section id="platdev-working-with-libraries">
        <title>Working With Libraries</title>

        <para>
            Libraries are an integral part of your system.
            This section describes some common practices you might find
            helpful when working with libraries to build your system:
            <itemizedlist>
                <listitem><para><link linkend='including-static-library-files'>How to include static library files</link>
                    </para></listitem>
                <listitem><para><link linkend='combining-multiple-versions-library-files-into-one-image'>How to use the Multilib feature to combine multiple versions of library files into a single image</link>
                    </para></listitem>
                <listitem><para><link linkend='installing-multiple-versions-of-the-same-library'>How to install multiple versions of the same library in parallel on the same system</link>
                    </para></listitem>
            </itemizedlist>
        </para>

        <section id='including-static-library-files'>
            <title>Including Static Library Files</title>

            <para>
                If you are building a library and the library offers static linking, you can control
                which static library files (<filename>*.a</filename> files) get included in the
                built library.
            </para>

            <para>
                The <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>
                and <ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES_*</filename></ulink>
                variables in the
                <filename>meta/conf/bitbake.conf</filename> configuration file define how files installed
                by the <filename>do_install</filename> task are packaged.
                By default, the <filename>PACKAGES</filename> variable contains
                <filename>${PN}-staticdev</filename>, which includes all static library files.
                <note>
                    Some previously released versions of the Yocto Project
                    defined the static library files through
                    <filename>${PN}-dev</filename>.
                </note>
                Following, is part of the BitBake configuration file.
                You can see where the static library files are defined:
                <literallayout class='monospaced'>
     PACKAGES = "${PN}-dbg ${PN} ${PN}-doc ${PN}-dev ${PN}-staticdev ${PN}-locale"
     PACKAGES_DYNAMIC = "${PN}-locale-*"
     FILES = ""

     FILES_${PN} = "${bindir}/* ${sbindir}/* ${libexecdir}/* ${libdir}/lib*${SOLIBS} \
                 ${sysconfdir} ${sharedstatedir} ${localstatedir} \
                 ${base_bindir}/* ${base_sbindir}/* \
                 ${base_libdir}/*${SOLIBS} \
                 ${datadir}/${BPN} ${libdir}/${BPN}/* \
                 ${datadir}/pixmaps ${datadir}/applications \
                 ${datadir}/idl ${datadir}/omf ${datadir}/sounds \
                 ${libdir}/bonobo/servers"

     FILES_${PN}-doc = "${docdir} ${mandir} ${infodir} ${datadir}/gtk-doc \
                 ${datadir}/gnome/help"
     SECTION_${PN}-doc = "doc"

     FILES_${PN}-dev = "${includedir} ${libdir}/lib*${SOLIBSDEV} ${libdir}/*.la \
                     ${libdir}/*.o ${libdir}/pkgconfig ${datadir}/pkgconfig \
                     ${datadir}/aclocal ${base_libdir}/*.o"
     SECTION_${PN}-dev = "devel"
     ALLOW_EMPTY_${PN}-dev = "1"
     RDEPENDS_${PN}-dev = "${PN} (= ${EXTENDPKGV})"

     FILES_${PN}-staticdev = "${libdir}/*.a ${base_libdir}/*.a"
     SECTION_${PN}-staticdev = "devel"
     RDEPENDS_${PN}-staticdev = "${PN}-dev (= ${EXTENDPKGV})"
                </literallayout>
            </para>
        </section>

        <section id="combining-multiple-versions-library-files-into-one-image">
            <title>Combining Multiple Versions of Library Files into One Image</title>

            <para>
                The build system offers the ability to build libraries with different
                target optimizations or architecture formats and combine these together
                into one system image.
                You can link different binaries in the image
                against the different libraries as needed for specific use cases.
                This feature is called "Multilib."
            </para>

            <para>
                An example would be where you have most of a system compiled in 32-bit
                mode using 32-bit libraries, but you have something large, like a database
                engine, that needs to be a 64-bit application and uses 64-bit libraries.
                Multilib allows you to get the best of both 32-bit and 64-bit libraries.
            </para>

            <para>
                While the Multilib feature is most commonly used for 32 and 64-bit differences,
                the approach the build system uses facilitates different target optimizations.
                You could compile some binaries to use one set of libraries and other binaries
                to use other different sets of libraries.
                The libraries could differ in architecture, compiler options, or other
                optimizations.
            </para>

            <para>
                This section overviews the Multilib process only.
                For more details on how to implement Multilib, see the
                <ulink url='&YOCTO_WIKI_URL;/wiki/Multilib'>Multilib</ulink> wiki
                page.
            </para>

            <para>
                Aside from this wiki page, several examples exist in the
                <filename>meta-skeleton</filename> layer found in the
               <link linkend='source-directory'>Source Directory</link>:
                <itemizedlist>
                    <listitem><para><filename>conf/multilib-example.conf</filename>
                        configuration file</para></listitem>
                    <listitem><para><filename>conf/multilib-example2.conf</filename>
                        configuration file</para></listitem>
                    <listitem><para><filename>recipes-multilib/images/core-image-multilib-example.bb</filename>
                        recipe</para></listitem>
                </itemizedlist>
            </para>

            <section id='preparing-to-use-multilib'>
                <title>Preparing to Use Multilib</title>

                <para>
                    User-specific requirements drive the Multilib feature.
                    Consequently, there is no one "out-of-the-box" configuration that likely
                    exists to meet your needs.
                </para>

                <para>
                    In order to enable Multilib, you first need to ensure your recipe is
                    extended to support multiple libraries.
                    Many standard recipes are already extended and support multiple libraries.
                    You can check in the <filename>meta/conf/multilib.conf</filename>
                    configuration file in the
                    <link linkend='source-directory'>Source Directory</link> to see how this is
                    done using the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-BBCLASSEXTEND'><filename>BBCLASSEXTEND</filename></ulink>
                    variable.
                    Eventually, all recipes will be covered and this list will
                    not be needed.
                </para>

                <para>
                    For the most part, the Multilib class extension works automatically to
                    extend the package name from <filename>${PN}</filename> to
                    <filename>${MLPREFIX}${PN}</filename>, where <filename>MLPREFIX</filename>
                    is the particular multilib (e.g. "lib32-" or "lib64-").
                    Standard variables such as
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-RPROVIDES'><filename>RPROVIDES</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'><filename>RRECOMMENDS</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>,
                    and <filename>PACKAGES_DYNAMIC</filename> are automatically extended by the system.
                    If you are extending any manual code in the recipe, you can use the
                    <filename>${MLPREFIX}</filename> variable to ensure those names are extended
                    correctly.
                    This automatic extension code resides in <filename>multilib.bbclass</filename>.
                </para>
            </section>

            <section id='using-multilib'>
                <title>Using Multilib</title>

                <para>
                    After you have set up the recipes, you need to define the actual
                    combination of multiple libraries you want to build.
                    You accomplish this through your <filename>local.conf</filename>
                    configuration file in the
                    <link linkend='build-directory'>Build Directory</link>.
                    An example configuration would be as follows:
                    <literallayout class='monospaced'>
     MACHINE = "qemux86-64"
     require conf/multilib.conf
     MULTILIBS = "multilib:lib32"
     DEFAULTTUNE_virtclass-multilib-lib32 = "x86"
     IMAGE_INSTALL = "lib32-connman"
                    </literallayout>
                    This example enables an
                    additional library named <filename>lib32</filename> alongside the
                    normal target packages.
                    When combining these "lib32" alternatives, the example uses "x86" for tuning.
                    For information on this particular tuning, see
                    <filename>meta/conf/machine/include/ia32/arch-ia32.inc</filename>.
                </para>

                <para>
                    The example then includes <filename>lib32-connman</filename>
                    in all the images, which illustrates one method of including a
                    multiple library dependency.
                    You can use a normal image build to include this dependency,
                    for example:
                    <literallayout class='monospaced'>
     $ bitbake core-image-sato
                    </literallayout>
                    You can also build Multilib packages specifically with a command like this:
                    <literallayout class='monospaced'>
     $  bitbake lib32-connman
                    </literallayout>
                </para>
            </section>

            <section id='additional-implementation-details'>
                <title>Additional Implementation Details</title>

                <para>
                    Different packaging systems have different levels of native Multilib
                    support.
                    For the RPM Package Management System, the following implementation details
                    exist:
                    <itemizedlist>
                        <listitem><para>A unique architecture is defined for the Multilib packages,
                            along with creating a unique deploy folder under
                            <filename>tmp/deploy/rpm</filename> in the
                            <link linkend='build-directory'>Build Directory</link>.
                            For example, consider <filename>lib32</filename> in a
                            <filename>qemux86-64</filename> image.
                            The possible architectures in the system are "all", "qemux86_64",
                            "lib32_qemux86_64", and "lib32_x86".</para></listitem>
                        <listitem><para>The <filename>${MLPREFIX}</filename> variable is stripped from
                            <filename>${PN}</filename> during RPM packaging.
                            The naming for a normal RPM package and a Multilib RPM package in a
                            <filename>qemux86-64</filename> system resolves to something similar to
                            <filename>bash-4.1-r2.x86_64.rpm</filename> and
                            <filename>bash-4.1.r2.lib32_x86.rpm</filename>, respectively.
                            </para></listitem>
                        <listitem><para>When installing a Multilib image, the RPM backend first
                            installs the base image and then installs the Multilib libraries.
                            </para></listitem>
                        <listitem><para>The build system relies on RPM to resolve the identical files in the
                            two (or more) Multilib packages.</para></listitem>
                    </itemizedlist>
                </para>

                <para>
                    For the IPK Package Management System, the following implementation details exist:
                    <itemizedlist>
                        <listitem><para>The <filename>${MLPREFIX}</filename> is not stripped from
                            <filename>${PN}</filename> during IPK packaging.
                            The naming for a normal RPM package and a Multilib IPK package in a
                            <filename>qemux86-64</filename> system resolves to something like
                            <filename>bash_4.1-r2.x86_64.ipk</filename> and
                            <filename>lib32-bash_4.1-rw_x86.ipk</filename>, respectively.
                            </para></listitem>
                        <listitem><para>The IPK deploy folder is not modified with
                            <filename>${MLPREFIX}</filename> because packages with and without
                            the Multilib feature can exist in the same folder due to the
                            <filename>${PN}</filename> differences.</para></listitem>
                        <listitem><para>IPK defines a sanity check for Multilib installation
                            using certain rules for file comparison, overridden, etc.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>
        </section>

        <section id='installing-multiple-versions-of-the-same-library'>
            <title>Installing Multiple Versions of the Same Library</title>

            <para>
                Situations can exist where you need to install and use
                multiple versions of the same library on the same system
                at the same time.
                These situations almost always exist when a library API
                changes and you have multiple pieces of software that
                depend on the separate versions of the library.
                To accommodate these situations, you can install multiple
                versions of the same library in parallel on the same system.
            </para>

            <para>
                The process is straight forward as long as the libraries use
                proper versioning.
                With properly versioned libraries, all you need to do to
                individually specify the libraries is create separate,
                appropriately named recipes where the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink> part of the
                name includes a portion that differentiates each library version
                (e.g.the major part of the version number).
                Thus, instead of having a single recipe that loads one version
                of a library (e.g. <filename>clutter</filename>), you provide
                multiple recipes that result in different versions
                of the libraries you want.
                As an example, the following two recipes would allow the
                two separate versions of the <filename>clutter</filename>
                library to co-exist on the same system:
                <literallayout class='monospaced'>
     clutter-1.6_1.6.20.bb
     clutter-1.8_1.8.4.bb
                </literallayout>
                Additionally, if you have other recipes that depend on a given
                library, you need to use the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
                variable to create the dependency.
                Continuing with the same example, if you want to have a recipe
                depend on the 1.8 version of the <filename>clutter</filename>
                library, use the following in your recipe:
                <literallayout class='monospaced'>
     DEPENDS = "clutter-1.8"
                </literallayout>
            </para>
        </section>
    </section>

    <section id='configuring-the-kernel'>
        <title>Configuring the Kernel</title>

        <para>
            Configuring the Yocto Project kernel consists of making sure the <filename>.config</filename>
            file has all the right information in it for the image you are building.
            You can use the <filename>menuconfig</filename> tool and configuration fragments to
            make sure your <filename>.config</filename> file is just how you need it.
            This section describes how to use <filename>menuconfig</filename>, create and use
            configuration fragments, and how to interactively tweak your <filename>.config</filename>
            file to create the leanest kernel configuration file possible.
        </para>

        <para>
            For more information on kernel configuration, see the
            "<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#changing-the-configuration'>Changing the Configuration</ulink>"
            section in the Yocto Project Linux Kernel Development Manual.
        </para>

        <section id='using-menuconfig'>
            <title>Using&nbsp;&nbsp;<filename>menuconfig</filename></title>

            <para>
                The easiest way to define kernel configurations is to set them through the
                <filename>menuconfig</filename> tool.
                This tool provides an interactive method with which
                to set kernel configurations.
                For general information on <filename>menuconfig</filename>, see
                <ulink url='http://en.wikipedia.org/wiki/Menuconfig'></ulink>.
            </para>

            <para>
                To use the <filename>menuconfig</filename> tool in the Yocto Project development
                environment, you must launch it using BitBake.
                Thus, the environment must be set up using the
                <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>
                or
                <ulink url='&YOCTO_DOCS_REF_URL;#structure-memres-core-script'><filename>oe-init-build-env-memres</filename></ulink>
                script found in the
                <link linkend='build-directory'>Build Directory</link>.
                The following commands run <filename>menuconfig</filename> assuming the
                <link linkend='source-directory'>Source Directory</link>
                top-level folder is <filename>~/poky</filename>:
                <literallayout class='monospaced'>
     $ cd poky
     $ source oe-init-build-env
     $ bitbake linux-yocto -c menuconfig
                </literallayout>
                Once <filename>menuconfig</filename> comes up, its standard interface allows you to
                interactively examine and configure all the kernel configuration parameters.
                After making your changes, simply exit the tool and save your changes to
                create an updated version of the <filename>.config</filename> configuration file.
            </para>

            <para>
                Consider an example that configures the <filename>linux-yocto-3.14</filename>
                kernel.
                The OpenEmbedded build system recognizes this kernel as
                <filename>linux-yocto</filename>.
                Thus, the following commands from the shell in which you previously sourced the
                environment initialization script cleans the shared state cache and the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>
                directory and then runs <filename>menuconfig</filename>:
                <literallayout class='monospaced'>
     $ bitbake linux-yocto -c menuconfig
                </literallayout>
            </para>

            <para>
                Once <filename>menuconfig</filename> launches, use the interface
                to navigate through the selections to find the configuration settings in
                which you are interested.
                For example, consider the <filename>CONFIG_SMP</filename> configuration setting.
                You can find it at <filename>Processor Type and Features</filename> under
                the configuration selection <filename>Symmetric Multi-processing Support</filename>.
                After highlighting the selection, use the arrow keys to select or deselect
                the setting.
                When you are finished with all your selections, exit out and save them.
            </para>

            <para>
                Saving the selections updates the <filename>.config</filename> configuration file.
                This is the file that the OpenEmbedded build system uses to configure the
                kernel during the build.
                You can find and examine this file in the Build Directory in
                <filename>tmp/work/</filename>.
                The actual <filename>.config</filename> is located in the area where the
                specific kernel is built.
                For example, if you were building a Linux Yocto kernel based on the
                Linux 3.14 kernel and you were building a QEMU image targeted for
                <filename>x86</filename> architecture, the
                <filename>.config</filename> file would be located here:
                <literallayout class='monospaced'>
     poky/build/tmp/work/qemux86-poky-linux/linux-yocto-3.14.11+git1+84f...
        ...656ed30-r1/linux-qemux86-standard-build
                </literallayout>
                <note>
                    The previous example directory is artificially split and many of the characters
                    in the actual filename are omitted in order to make it more readable.
                    Also, depending on the kernel you are using, the exact pathname
                    for <filename>linux-yocto-3.14...</filename> might differ.
                </note>
            </para>

            <para>
                Within the <filename>.config</filename> file, you can see the kernel settings.
                For example, the following entry shows that symmetric multi-processor support
                is not set:
                <literallayout class='monospaced'>
     # CONFIG_SMP is not set
                </literallayout>
            </para>

            <para>
                A good method to isolate changed configurations is to use a combination of the
                <filename>menuconfig</filename> tool and simple shell commands.
                Before changing configurations with <filename>menuconfig</filename>, copy the
                existing <filename>.config</filename> and rename it to something else,
                use <filename>menuconfig</filename> to make
                as many changes as you want and save them, then compare the renamed configuration
                file against the newly created file.
                You can use the resulting differences as your base to create configuration fragments
                to permanently save in your kernel layer.
                <note>
                    Be sure to make a copy of the <filename>.config</filename> and don't just
                    rename it.
                    The build system needs an existing <filename>.config</filename>
                    from which to work.
                </note>
            </para>
        </section>

        <section id='creating-config-fragments'>
            <title>Creating Configuration Fragments</title>

            <para>
                Configuration fragments are simply kernel options that appear in a file
                placed where the OpenEmbedded build system can find and apply them.
                Syntactically, the configuration statement is identical to what would appear
                in the <filename>.config</filename> file, which is in the
                <link linkend='build-directory'>Build Directory</link> in
                <filename>tmp/work/&lt;arch&gt;-poky-linux/linux-yocto-&lt;release-specific-string&gt;/linux-&lt;arch&gt;-&lt;build-type&gt;</filename>.
            </para>

            <para>
                It is simple to create a configuration fragment.
                For example, issuing the following from the shell creates a configuration fragment
                file named <filename>my_smp.cfg</filename> that enables multi-processor support
                within the kernel:
                <literallayout class='monospaced'>
     $ echo "CONFIG_SMP=y" >> my_smp.cfg
                </literallayout>
                <note>
                    All configuration files must use the <filename>.cfg</filename> extension in order
                    for the OpenEmbedded build system to recognize them as a configuration fragment.
                </note>
            </para>

            <para>
                Where do you put your configuration files?
                You can place these configuration files in the same area pointed to by
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>.
                The OpenEmbedded build system will pick up the configuration and add it to the
                kernel's configuration.
                For example, suppose you had a set of configuration options in a file called
                <filename>myconfig.cfg</filename>.
                If you put that file inside a directory named <filename>linux-yocto</filename>
                that resides in the same directory as the kernel's append file and then add
                a <filename>SRC_URI</filename> statement such as the following to the kernel's append file,
                those configuration options will be picked up and applied when the kernel is built.
                <literallayout class='monospaced'>
     SRC_URI += "file://myconfig.cfg"
                </literallayout>
            </para>

            <para>
                As mentioned earlier, you can group related configurations into multiple files and
                name them all in the <filename>SRC_URI</filename> statement as well.
                For example, you could group separate configurations specifically for Ethernet and graphics
                into their own files and add those by using a <filename>SRC_URI</filename> statement like the
                following in your append file:
                <literallayout class='monospaced'>
     SRC_URI += "file://myconfig.cfg \
            file://eth.cfg \
            file://gfx.cfg"
                </literallayout>
            </para>
        </section>

        <section id='fine-tuning-the-kernel-configuration-file'>
            <title>Fine-Tuning the Kernel Configuration File</title>

            <para>
                You can make sure the <filename>.config</filename> file is as lean or efficient as
                possible by reading the output of the kernel configuration fragment audit,
                noting any issues, making changes to correct the issues, and then repeating.
            </para>

            <para>
                As part of the kernel build process, the
                <filename>kernel_configcheck</filename> task runs.
                This task validates the kernel configuration by checking the final
                <filename>.config</filename> file against the input files.
                During the check, the task produces warning messages for the following
                issues:
                <itemizedlist>
                    <listitem><para>Requested options that did not make the final
                        <filename>.config</filename> file.</para></listitem>
                    <listitem><para>Configuration items that appear twice in the same
                        configuration fragment.</para></listitem>
                    <listitem><para>Configuration items tagged as "required" that were overridden.
                        </para></listitem>
                    <listitem><para>A board overrides a non-board specific option.</para></listitem>
                    <listitem><para>Listed options not valid for the kernel being processed.
                        In other words, the option does not appear anywhere.</para></listitem>
                </itemizedlist>
                <note>
                    The <filename>kernel_configcheck</filename> task can also optionally report
                    if an option is overridden during processing.
                </note>
            </para>

            <para>
                For each output warning, a message points to the file
                that contains a list of the options and a pointer to the config
                fragment that defines them.
                Collectively, the files are the key to streamlining the configuration.
            </para>

            <para>
                To streamline the configuration, do the following:
                <orderedlist>
                    <listitem><para>Start with a full configuration that you know
                        works - it builds and boots successfully.
                        This configuration file will be your baseline.</para></listitem>
                    <listitem><para>Separately run the <filename>configme</filename> and
                        <filename>kernel_configcheck</filename> tasks.</para></listitem>
                    <listitem><para>Take the resulting list of files from the
                        <filename>kernel_configcheck</filename> task warnings and do the following:
                        <itemizedlist>
                            <listitem><para>Drop values that are redefined in the fragment but do not
                                change the final <filename>.config</filename> file.</para></listitem>
                            <listitem><para>Analyze and potentially drop values from the
                                <filename>.config</filename> file that override required
                                configurations.</para></listitem>
                            <listitem><para>Analyze and potentially remove non-board specific options.
                                </para></listitem>
                            <listitem><para>Remove repeated and invalid options.</para></listitem>
                        </itemizedlist></para></listitem>
                    <listitem><para>After you have worked through the output of the kernel configuration
                        audit, you can re-run the <filename>configme</filename>
                        and <filename>kernel_configcheck</filename> tasks to see the results of your
                        changes.
                        If you have more issues, you can deal with them as described in the
                        previous step.</para></listitem>
                </orderedlist>
            </para>

            <para>
                Iteratively working through steps two through four eventually yields
                a minimal, streamlined configuration file.
                Once you have the best <filename>.config</filename>, you can build the Linux
                Yocto kernel.
            </para>
        </section>
    </section>

    <section id="patching-the-kernel">
        <title>Patching the Kernel</title>

        <para>
            Patching the kernel involves changing or adding configurations to an existing kernel,
            changing or adding recipes to the kernel that are needed to support specific hardware features,
            or even altering the source code itself.
            <note>
                You can use the <filename>yocto-kernel</filename> script
                found in the <link linkend='source-directory'>Source Directory</link>
                under <filename>scripts</filename> to manage kernel patches and configuration.
                See the "<ulink url='&YOCTO_DOCS_BSP_URL;#managing-kernel-patches-and-config-items-with-yocto-kernel'>Managing kernel Patches and Config Items with yocto-kernel</ulink>"
                section in the Yocto Project Board Support Packages (BSP) Developer's Guide for
                more information.</note>
        </para>

        <para>
            This example creates a simple patch by adding some QEMU emulator console
            output at boot time through <filename>printk</filename> statements in the kernel's
            <filename>calibrate.c</filename> source code file.
            Applying the patch and booting the modified image causes the added
            messages to appear on the emulator's console.
        </para>

        <para>
            The example assumes a clean build exists for the <filename>qemux86</filename>
            machine in a
            <link linkend='source-directory'>Source Directory</link>
            named <filename>poky</filename>.
            Furthermore, the <link linkend='build-directory'>Build Directory</link> is
            <filename>build</filename> and is located in <filename>poky</filename> and
            the kernel is based on the Linux 3.4 kernel.
            For general information on how to configure the most efficient build, see the
            "<ulink url='&YOCTO_DOCS_QS_URL;#building-image'>Building an Image</ulink>" section
            in the Yocto Project Quick Start.
        </para>

        <para>
            Also, for more information on patching the kernel, see the
            "<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#applying-patches'>Applying Patches</ulink>"
            section in the Yocto Project Linux Kernel Development Manual.
        </para>

        <section id='create-a-layer-for-your-changes'>
            <title>Create a Layer for your Changes</title>

            <para>
                The first step is to create a layer so you can isolate your
                changes.
                Rather than use the <filename>yocto-layer</filename> script
                to create the layer, this example steps through the process
                by hand.
                If you want information on the script that creates a general
                layer, see the
                "<link linkend='creating-a-general-layer-using-the-yocto-layer-script'>Creating a General Layer Using the yocto-layer Script</link>"
                section.
            </para>

            <para>
                These two commands create a directory you can use for your
                layer:
                <literallayout class='monospaced'>
     $ cd ~/poky
     $ mkdir meta-mylayer
                </literallayout>
                Creating a directory that follows the Yocto Project layer naming
                conventions sets up the layer for your changes.
                The layer is where you place your configuration files, append
                files, and patch files.
                To learn more about creating a layer and filling it with the
                files you need, see the "<link linkend='understanding-and-creating-layers'>Understanding
                and Creating Layers</link>" section.
            </para>
        </section>

        <section id='finding-the-kernel-source-code'>
            <title>Finding the Kernel Source Code</title>

            <para>
                Each time you build a kernel image, the kernel source code is fetched
                and unpacked into the following directory:
                <literallayout class='monospaced'>
     ${S}/linux
                </literallayout>
                See the "<link linkend='finding-the-temporary-source-code'>Finding the Temporary Source Code</link>"
                section and the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink> variable
                for more information about where source is kept during a build.
            </para>

            <para>
                For this example, we are going to patch the
                <filename>init/calibrate.c</filename> file
                by adding some simple console <filename>printk</filename> statements that we can
                see when we boot the image using QEMU.
            </para>
        </section>

        <section id='creating-the-patch'>
            <title>Creating the Patch</title>

            <para>
                Two methods exist by which you can create the patch:
                <link linkend='using-a-git-workflow'>Git workflow</link> and
                <link linkend='using-a-quilt-workflow'>Quilt workflow</link>.
                For kernel patches, the Git workflow is more appropriate.
                This section assumes the Git workflow and shows the steps specific to
                this example.
                <orderedlist>
                    <listitem><para><emphasis>Change the working directory</emphasis>:
                        Change to where the kernel source code is before making
                        your edits to the <filename>calibrate.c</filename> file:
                        <literallayout class='monospaced'>
     $ cd ~/poky/build/tmp/work/qemux86-poky-linux/linux-yocto-${PV}-${PR}/linux
                        </literallayout>
                        Because you are working in an established Git repository,
                        you must be in this directory in order to commit your changes
                        and create the patch file.
                        <note>The <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink> and
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink> variables
                            represent the version and revision for the
                            <filename>linux-yocto</filename> recipe.
                            The <filename>PV</filename> variable includes the Git meta and machine
                            hashes, which make the directory name longer than you might
                            expect.
                        </note></para></listitem>
                    <listitem><para><emphasis>Edit the source file</emphasis>:
                        Edit the <filename>init/calibrate.c</filename> file to have the
                        following changes:
                        <literallayout class='monospaced'>
     void calibrate_delay(void)
     {
         unsigned long lpj;
         static bool printed;
         int this_cpu = smp_processor_id();

         printk("*************************************\n");
         printk("*                                   *\n");
         printk("*        HELLO YOCTO KERNEL         *\n");
         printk("*                                   *\n");
         printk("*************************************\n");

     	if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {
               .
               .
               .
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Stage and commit your changes</emphasis>:
                        These Git commands display the modified file, stage it, and then
                        commit the file:
                        <literallayout class='monospaced'>
     $ git status
     $ git add init/calibrate.c
     $ git commit -m "calibrate: Add printk example"
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Generate the patch file</emphasis>:
                        This Git command creates the a patch file named
                        <filename>0001-calibrate-Add-printk-example.patch</filename>
                        in the current directory.
                        <literallayout class='monospaced'>
     $ git format-patch -1
                        </literallayout>
                        </para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='set-up-your-layer-for-the-build'>
            <title>Set Up Your Layer for the Build</title>

            <para>These steps get your layer set up for the build:
                <orderedlist>
                    <listitem><para><emphasis>Create additional structure</emphasis>:
                        Create the additional layer structure:
                        <literallayout class='monospaced'>
     $ cd ~/poky/meta-mylayer
     $ mkdir conf
     $ mkdir recipes-kernel
     $ mkdir recipes-kernel/linux
     $ mkdir recipes-kernel/linux/linux-yocto
                         </literallayout>
                         The <filename>conf</filename> directory holds your configuration files, while the
                         <filename>recipes-kernel</filename> directory holds your append file and
                         your patch file.</para></listitem>
                    <listitem><para><emphasis>Create the layer configuration file</emphasis>:
                        Move to the <filename>meta-mylayer/conf</filename> directory and create
                        the <filename>layer.conf</filename> file as follows:
                        <literallayout class='monospaced'>
     # We have a conf and classes directory, add to BBPATH
     BBPATH .= ":${LAYERDIR}"

     # We have recipes-* directories, add to BBFILES
     BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
                 ${LAYERDIR}/recipes-*/*/*.bbappend"

     BBFILE_COLLECTIONS += "mylayer"
     BBFILE_PATTERN_mylayer = "^${LAYERDIR}/"
     BBFILE_PRIORITY_mylayer = "5"
                         </literallayout>
                         Notice <filename>mylayer</filename> as part of the last three
                         statements.</para></listitem>
                    <listitem><para><emphasis>Create the kernel recipe append file</emphasis>:
                        Move to the <filename>meta-mylayer/recipes-kernel/linux</filename> directory and create
                        the <filename>linux-yocto_3.4.bbappend</filename> file as follows:
                        <literallayout class='monospaced'>
     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"

     SRC_URI += "file://0001-calibrate-Add-printk-example.patch"
                        </literallayout>
                        The <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
                        and <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                        statements enable the OpenEmbedded build system to find the patch file.
                        For more information on using append files, see the
                        "<link linkend='using-bbappend-files'>Using .bbappend Files</link>"
                        section.
                        </para></listitem>
                    <listitem><para><emphasis>Put the patch file in your layer</emphasis>:
                        Move the <filename>0001-calibrate-Add-printk-example.patch</filename> file to
                        the <filename>meta-mylayer/recipes-kernel/linux/linux-yocto</filename>
                        directory.</para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='set-up-for-the-build'>
            <title>Set Up for the Build</title>

            <para>
                Do the following to make sure the build parameters are set up for the example.
                Once you set up these build parameters, they do not have to change unless you
                change the target architecture of the machine you are building:
                <itemizedlist>
                    <listitem><para><emphasis>Build for the correct target architecture:</emphasis> Your
                        selected <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
                        definition within the <filename>local.conf</filename> file in the
                        <link linkend='build-directory'>Build Directory</link>
                        specifies the target architecture used when building the Linux kernel.
                        By default, <filename>MACHINE</filename> is set to
                        <filename>qemux86</filename>, which specifies a 32-bit
                        <trademark class='registered'>Intel</trademark> Architecture
                        target machine suitable for the QEMU emulator.</para></listitem>
                    <listitem><para><emphasis>Identify your <filename>meta-mylayer</filename>
                        layer:</emphasis> The
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-BBLAYERS'><filename>BBLAYERS</filename></ulink>
                        variable in the
                        <filename>bblayers.conf</filename> file found in the
                        <filename>poky/build/conf</filename> directory needs to have the path to your local
                        <filename>meta-mylayer</filename> layer.
                        By default, the <filename>BBLAYERS</filename> variable contains paths to
                        <filename>meta</filename>, <filename>meta-yocto</filename>, and
                        <filename>meta-yocto-bsp</filename> in the
                        <filename>poky</filename> Git repository.
                        Add the path to your <filename>meta-mylayer</filename> location:
                        <literallayout class='monospaced'>
     BBLAYERS ?= " \
       $HOME/poky/meta \
       $HOME/poky/meta-yocto \
       $HOME/poky/meta-yocto-bsp \
       $HOME/poky/meta-mylayer \
       "

     BBLAYERS_NON_REMOVABLE ?= " \
       $HOME/poky/meta \
       $HOME/poky/meta-yocto \
       "
                        </literallayout></para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='build-the-modified-qemu-kernel-image'>
            <title>Build the Modified QEMU Kernel Image</title>

            <para>
                The following steps build your modified kernel image:
                <orderedlist>
                    <listitem><para><emphasis>Be sure your build environment is initialized</emphasis>:
                        Your environment should be set up since you previously sourced
                        the
                        <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>
                        script.
                        If it is not, source the script again from <filename>poky</filename>.
                        <literallayout class='monospaced'>
     $ cd ~/poky
     $ source &OE_INIT_FILE;
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Clean up</emphasis>:
                        Be sure to clean the shared state out by running the
                        <filename>cleansstate</filename> BitBake task as follows from your Build Directory:
                        <literallayout class='monospaced'>
     $ bitbake -c cleansstate linux-yocto
                        </literallayout></para>
                        <para><note>Never remove any files by hand from the <filename>tmp/deploy</filename>
                        directory inside the
                        <link linkend='build-directory'>Build Directory</link>.
                        Always use the various BitBake clean tasks to clear out previous
                        build artifacts.
                        </note></para></listitem>
                    <listitem><para><emphasis>Build the image</emphasis>:
                        Next, build the kernel image using this command:
                        <literallayout class='monospaced'>
     $ bitbake -k linux-yocto
                        </literallayout></para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='boot-the-image-and-verify-your-changes'>
            <title>Boot the Image and Verify Your Changes</title>

            <para>
                These steps boot the image and allow you to see the changes
                <orderedlist>
                    <listitem><para><emphasis>Boot the image</emphasis>:
                        Boot the modified image in the QEMU emulator
                        using this command:
                        <literallayout class='monospaced'>
     $ runqemu qemux86
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Verify the changes</emphasis>:
                        Log into the machine using <filename>root</filename> with no password and then
                        use the following shell command to scroll through the console's boot output.
                        <literallayout class='monospaced'>
     # dmesg | less
                        </literallayout>
                        You should see the results of your <filename>printk</filename> statements
                        as part of the output.</para></listitem>
                </orderedlist>
            </para>
        </section>
    </section>

    <section id='making-images-more-secure'>
        <title>Making Images More Secure</title>

        <para>
            The Yocto Project has security flags that you can enable that
            help make your build output more secure.
            The security flags are in the
            <filename>meta/conf/distro/include/security_flags.inc</filename>
            file in your
            <link linkend='source-directory'>Source Directory</link>
            (e.g. <filename>poky</filename>).
        </para>

        <para>
            These GCC/LD flags enable more secure code generation.
            By including the <filename>security_flags.inc</filename>
            file, you enable flags to the compiler and linker that cause
            them to generate more secure code.
            <note>
                These flags are enabled by default in the
                <filename>poky-lsb</filename> distribution.
            </note>
            Use the following line in your
            <filename>local.conf</filename> file
            to enable the security compiler and
            linker flags to your build:
            <literallayout class='monospaced'>
     require conf/distro/include/security_flags.inc
            </literallayout>
        </para>
    </section>

    <section id='creating-your-own-distribution'>
        <title>Creating Your Own Distribution</title>

        <para>
            When you build an image using the Yocto Project and
            do not alter any distribution
            <link linkend='metadata'>Metadata</link>, you are creating a
            Poky distribution.
            If you wish to gain more control over package alternative
            selections, compile-time options, and other low-level
            configurations, you can create your own distribution.
        </para>

        <para>
            To create your own distribution, the basic steps consist of
            creating your own distribution layer, creating your own
            distribution configuration file, and then adding any needed
            code and Metadata to the layer.
            The following steps provide some more detail:
            <itemizedlist>
                <listitem><para><emphasis>Create a layer for your new distro:</emphasis>
                    Create your distribution layer so that you can keep your
                    Metadata and code for the distribution separate.
                    It is strongly recommended that you create and use your own
                    layer for configuration and code.
                    Using your own layer as compared to just placing
                    configurations in a <filename>local.conf</filename>
                    configuration file makes it easier to reproduce the same
                    build configuration when using multiple build machines.
                    See the
                    "<link linkend='creating-a-general-layer-using-the-yocto-layer-script'>Creating a General Layer Using the yocto-layer Script</link>"
                    section for information on how to quickly set up a layer.
                    </para></listitem>
                <listitem><para><emphasis>Create the distribution configuration file:</emphasis>
                    The distribution configuration file needs to be created in
                    the <filename>conf/distro</filename> directory of your
                    layer.
                    You need to name it using your distribution name
                    (e.g. <filename>mydistro.conf</filename>).
                    <note>
                        The
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink>
                        variable in your
                        <filename>local.conf</filename> file determines the
                        name of your distribution.
                    </note></para>
                    <para>You can split out parts of your configuration file
                    into include files and then "require" them from within
                    your distribution configuration file.
                    Be sure to place the include files in the
                    <filename>conf/distro/include</filename> directory of
                    your layer.
                    A common example usage of include files would be to
                    separate out the selection of desired version and revisions
                    for individual recipes.
</para>
                    <para>Your configuration file needs to set the following
                    required variables:
                    <literallayout class='monospaced'>
     <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_NAME'><filename>DISTRO_NAME</filename></ulink>
     <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_VERSION'><filename>DISTRO_VERSION</filename></ulink>
                    </literallayout>
                    These following variables are optional and you typically
                    set them from the distribution configuration file:
                    <literallayout class='monospaced'>
     <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></ulink>
     <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_EXTRA_RDEPENDS'><filename>DISTRO_EXTRA_RDEPENDS</filename></ulink>
     <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_EXTRA_RRECOMMENDS'><filename>DISTRO_EXTRA_RRECOMMENDS</filename></ulink>
     <ulink url='&YOCTO_DOCS_REF_URL;#var-TCLIBC'><filename>TCLIBC</filename></ulink>
                    </literallayout>
                    <tip>
                        If you want to base your distribution configuration file
                        on the very basic configuration from OE-Core, you
                        can use
                        <filename>conf/distro/defaultsetup.conf</filename> as
                        a reference and just include variables that differ
                        as compared to <filename>defaultsetup.conf</filename>.
                        Alternatively, you can create a distribution
                        configuration file from scratch using the
                        <filename>defaultsetup.conf</filename> file
                        or configuration files from other distributions
                        such as Poky or Angstrom as references.
                    </tip></para></listitem>
                <listitem><para><emphasis>Provide miscellaneous variables:</emphasis>
                    Be sure to define any other variables for which you want to
                    create a default or enforce as part of the distribution
                    configuration.
                    You can include nearly any variable from the
                    <filename>local.conf</filename> file.
                    The variables you use are not limited to the list in the
                    previous bulleted item.</para></listitem>
                <listitem><para><emphasis>Point to Your distribution configuration file:</emphasis>
                    In your <filename>local.conf</filename> file in the
                    <link linkend='build-directory'>Build Directory</link>,
                    set your
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink>
                    variable to point to your distribution's configuration file.
                    For example, if your distribution's configuration file is
                    named <filename>mydistro.conf</filename>, then you point
                    to it as follows:
                    <literallayout class='monospaced'>
     DISTRO = "mydistro"
                    </literallayout></para></listitem>
                <listitem><para><emphasis>Add more to the layer if necessary:</emphasis>
                    Use your layer to hold other information needed for the
                    distribution:
                    <itemizedlist>
                        <listitem><para>Add recipes for installing
                            distro-specific configuration files that are not
                            already installed by another recipe.
                            If you have distro-specific configuration files
                            that are included by an existing recipe, you should
                            add an append file (<filename>.bbappend</filename>)
                            for those.
                            For general information and recommendations
                            on how to add recipes to your layer, see the
                            "<link linkend='creating-your-own-layer'>Creating Your Own Layer</link>"
                            and
                            "<link linkend='best-practices-to-follow-when-creating-layers'>Best Practices to Follow When Creating Layers</link>"
                            sections.</para></listitem>
                        <listitem><para>Add any image recipes that are specific
                            to your distribution.</para></listitem>
                        <listitem><para>Add a <filename>psplash</filename>
                            append file for a branded splash screen.
                            For information on append files, see the
                            "<link linkend='using-bbappend-files'>Using .bbappend Files</link>"
                            section.</para></listitem>
                        <listitem><para>Add any other append files to make
                            custom changes that are specific to individual
                            recipes.</para></listitem>
                    </itemizedlist></para></listitem>
            </itemizedlist>
        </para>
    </section>

    <section id='building-a-tiny-system'>
        <title>Building a Tiny System</title>

        <para>
            Very small distributions have some significant advantages such
            as requiring less on-die or in-package memory (cheaper), better
            performance through efficient cache usage, lower power requirements
            due to less memory, faster boot times, and reduced development
            overhead.
            Some real-world examples where a very small distribution gives
            you distinct advantages are digital cameras, medical devices,
            and small headless systems.
        </para>

        <para>
            This section presents information that shows you how you can
            trim your distribution to even smaller sizes than the
            <filename>poky-tiny</filename> distribution, which is around
            5 Mbytes, that can be built out-of-the-box using the Yocto Project.
        </para>

        <section id='tiny-system-overview'>
            <title>Overview</title>

            <para>
                The following list presents the overall steps you need to
                consider and perform to create distributions with smaller
                root filesystems, achieve faster boot times, maintain your critical
                functionality, and avoid initial RAM disks:
                <itemizedlist>
                    <listitem><para>
                        <link linkend='goals-and-guiding-principles'>Determine your goals and guiding principles.</link>
                        </para></listitem>
                    <listitem><para>
                        <link linkend='understand-what-gives-your-image-size'>Understand what contributes to your image size.</link>
                        </para></listitem>
                    <listitem><para>
                        <link linkend='trim-the-root-filesystem'>Reduce the size of the root filesystem.</link>
                        </para></listitem>
                    <listitem><para>
                        <link linkend='trim-the-kernel'>Reduce the size of the kernel.</link>
                        </para></listitem>
                    <listitem><para>
                        <link linkend='remove-package-management-requirements'>Eliminate packaging requirements.</link>
                        </para></listitem>
                    <listitem><para>
                        <link linkend='look-for-other-ways-to-minimize-size'>Look for other ways to minimize size.</link>
                        </para></listitem>
                    <listitem><para>
                        <link linkend='iterate-on-the-process'>Iterate on the process.</link>
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='goals-and-guiding-principles'>
            <title>Goals and Guiding Principles</title>

            <para>
                Before you can reach your destination, you need to know
                where you are going.
                Here is an example list that you can use as a guide when
                creating very small distributions:
                <itemizedlist>
                    <listitem><para>Determine how much space you need
                        (e.g. a kernel that is 1 Mbyte or less and
                        a root filesystem that is 3 Mbytes or less).
                        </para></listitem>
                    <listitem><para>Find the areas that are currently
                        taking 90% of the space and concentrate on reducing
                        those areas.
                        </para></listitem>
                    <listitem><para>Do not create any difficult "hacks"
                        to achieve your goals.</para></listitem>
                    <listitem><para>Leverage the device-specific
                        options.</para></listitem>
                    <listitem><para>Work in a separate layer so that you
                        keep changes isolated.
                        For information on how to create layers, see
                        the "<link linkend='understanding-and-creating-layers'>Understanding and Creating Layers</link>" section.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='understand-what-gives-your-image-size'>
            <title>Understand What Contributes to Your Image Size</title>

            <para>
                It is easiest to have something to start with when creating
                your own distribution.
                You can use the Yocto Project out-of-the-box to create the
                <filename>poky-tiny</filename> distribution.
                Ultimately, you will want to make changes in your own
                distribution that are likely modeled after
                <filename>poky-tiny</filename>.
                <note>
                    To use <filename>poky-tiny</filename> in your build,
                    set the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink>
                    variable in your
                    <filename>local.conf</filename> file to "poky-tiny"
                    as described in the
                    "<link linkend='creating-your-own-distribution'>Creating Your Own Distribution</link>"
                    section.
                </note>
            </para>

            <para>
                Understanding some memory concepts will help you reduce the
                system size.
                Memory consists of static, dynamic, and temporary memory.
                Static memory is the TEXT (code), DATA (initialized data
                in the code), and BSS (uninitialized data) sections.
                Dynamic memory represents memory that is allocated at runtime:
                stacks, hash tables, and so forth.
                Temporary memory is recovered after the boot process.
                This memory consists of memory used for decompressing
                the kernel and for the <filename>__init__</filename>
                functions.
            </para>

            <para>
                To help you see where you currently are with kernel and root
                filesystem sizes, you can use two tools found in the
                <link linkend='source-directory'>Source Directory</link> in
                the <filename>scripts/tiny/</filename> directory:
                <itemizedlist>
                    <listitem><para><filename>ksize.py</filename>: Reports
                        component sizes for the kernel build objects.
                        </para></listitem>
                    <listitem><para><filename>dirsize.py</filename>: Reports
                        component sizes for the root filesystem.</para></listitem>
                </itemizedlist>
                This next tool and command help you organize configuration
                fragments and view file dependencies in a human-readable form:
                <itemizedlist>
                    <listitem><para><filename>merge_config.sh</filename>:
                        Helps you manage configuration files and fragments
                        within the kernel.
                        With this tool, you can merge individual configuration
                        fragments together.
                        The tool allows you to make overrides and warns you
                        of any missing configuration options.
                        The tool is ideal for allowing you to iterate on
                        configurations, create minimal configurations, and
                        create configuration files for different machines
                        without having to duplicate your process.</para>
                        <para>The <filename>merge_config.sh</filename> script is
                        part of the Linux Yocto kernel Git repositories
                        (i.e. <filename>linux-yocto-3.14</filename>,
                        <filename>linux-yocto-3.10</filename>,
                        <filename>linux-yocto-3.8</filename>, and so forth)
                        in the
                        <filename>scripts/kconfig</filename> directory.</para>
                        <para>For more information on configuration fragments,
                        see the
                        "<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#generating-configuration-files'>Generating Configuration Files</ulink>"
                        section of the Yocto Project Linux Kernel Development
                        Manual and the "<link linkend='creating-config-fragments'>Creating Configuration Fragments</link>"
                        section, which is in this manual.</para></listitem>
                    <listitem><para><filename>bitbake -u depexp -g &lt;bitbake_target&gt;</filename>:
                        Using the BitBake command with these options brings up
                        a Dependency Explorer from which you can view file
                        dependencies.
                        Understanding these dependencies allows you to make
                        informed decisions when cutting out various pieces of the
                        kernel and root filesystem.</para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='trim-the-root-filesystem'>
            <title>Trim the Root Filesystem</title>

            <para>
                The root filesystem is made up of packages for booting,
                libraries, and applications.
                To change things, you can configure how the packaging happens,
                which changes the way you build them.
                You can also tweak the filesystem itself or select a different
                filesystem.
            </para>

            <para>
                First, find out what is hogging your root filesystem by running the
                <filename>dirsize.py</filename> script from your root directory:
                <literallayout class='monospaced'>
     $ cd &lt;root-directory-of-image&gt;
     $ dirsize.py 100000 > dirsize-100k.log
     $ cat dirsize-100k.log
                </literallayout>
                You can apply a filter to the script to ignore files under
                a certain size.
                The previous example filters out any files below 100 Kbytes.
                The sizes reported by the tool are uncompressed, and thus
                will be smaller by a relatively constant factor in a
                compressed root filesystem.
                When you examine your log file, you can focus on areas of the
                root filesystem that take up large amounts of memory.
            </para>

            <para>
                You need to be sure that what you eliminate does not cripple
                the functionality you need.
                One way to see how packages relate to each other is by using
                the Dependency Explorer UI with the BitBake command:
                <literallayout class='monospaced'>
     $ cd &lt;image-directory&gt;
     $ bitbake -u depexp -g &lt;image&gt;
                </literallayout>
                Use the interface to select potential packages you wish to
                eliminate and see their dependency relationships.
            </para>

            <para>
                When deciding how to reduce the size, get rid of packages that
                result in minimal impact on the feature set.
                For example, you might not need a VGA display.
                Or, you might be able to get by with <filename>devtmpfs</filename>
                and <filename>mdev</filename> instead of
                <filename>udev</filename>.
            </para>

            <para>
                Use your <filename>local.conf</filename> file to make changes.
                For example, to eliminate <filename>udev</filename> and
                <filename>glib</filename>, set the following in the
                local configuration file:
                <literallayout class='monospaced'>
     VIRTUAL-RUNTIME_dev_manager = ""
                </literallayout>
            </para>

            <para>
                Finally, you should consider exactly the type of root
                filesystem you need to meet your needs while also reducing
                its size.
                For example, consider <filename>cramfs</filename>,
                <filename>squashfs</filename>, <filename>ubifs</filename>,
                <filename>ext2</filename>, or an <filename>initramfs</filename>
                using <filename>initramfs</filename>.
                Be aware that <filename>ext3</filename> requires a 1 Mbyte
                journal.
                If you are okay with running read-only, you do not need this
                journal.
            </para>

            <note>
                After each round of elimination, you need to rebuild your
                system and then use the tools to see the effects of your
                reductions.
            </note>


        </section>

        <section id='trim-the-kernel'>
            <title>Trim the Kernel</title>

            <para>
                The kernel is built by including policies for hardware-independent
                aspects.
                What subsystems do you enable?
                For what architecture are you building?
                Which drivers do you build by default?
                <note>You can modify the kernel source if you want to help
                    with boot time.
                </note>
            </para>

            <para>
                Run the <filename>ksize.py</filename> script from the top-level
                Linux build directory to get an idea of what is making up
                the kernel:
                <literallayout class='monospaced'>
     $ cd &lt;top-level-linux-build-directory&gt;
     $ ksize.py > ksize.log
     $ cat ksize.log
                </literallayout>
                When you examine the log, you will see how much space is
                taken up with the built-in <filename>.o</filename> files for
                drivers, networking, core kernel files, filesystem, sound,
                and so forth.
                The sizes reported by the tool are uncompressed, and thus
                will be smaller by a relatively constant factor in a compressed
                kernel image.
                Look to reduce the areas that are large and taking up around
                the "90% rule."
            </para>

            <para>
                To examine, or drill down, into any particular area, use the
                <filename>-d</filename> option with the script:
                <literallayout class='monospaced'>
     $ ksize.py -d > ksize.log
                </literallayout>
                Using this option breaks out the individual file information
                for each area of the kernel (e.g. drivers, networking, and
                so forth).
            </para>

            <para>
                Use your log file to see what you can eliminate from the kernel
                based on features you can let go.
                For example, if you are not going to need sound, you do not
                need any drivers that support sound.
            </para>

            <para>
                After figuring out what to eliminate, you need to reconfigure
                the kernel to reflect those changes during the next build.
                You could run <filename>menuconfig</filename> and make all your
                changes at once.
                However, that makes it difficult to see the effects of your
                individual eliminations and also makes it difficult to replicate
                the changes for perhaps another target device.
                A better method is to start with no configurations using
                <filename>allnoconfig</filename>, create configuration
                fragments for individual changes, and then manage the
                fragments into a single configuration file using
                <filename>merge_config.sh</filename>.
                The tool makes it easy for you to iterate using the
                configuration change and build cycle.
            </para>

            <para>
                Each time you make configuration changes, you need to rebuild
                the kernel and check to see what impact your changes had on
                the overall size.
            </para>
        </section>

        <section id='remove-package-management-requirements'>
            <title>Remove Package Management Requirements</title>

            <para>
                Packaging requirements add size to the image.
                One way to reduce the size of the image is to remove all the
                packaging requirements from the image.
                This reduction includes both removing the package manager
                and its unique dependencies as well as removing the package
                management data itself.
            </para>

            <para>
                To eliminate all the packaging requirements for an image,
                be sure that "package-management" is not part of your
                <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
                statement for the image.
                When you remove this feature, you are removing the package
                manager as well as its dependencies from the root filesystem.
            </para>
        </section>

        <section id='look-for-other-ways-to-minimize-size'>
            <title>Look for Other Ways to Minimize Size</title>

            <para>
                Depending on your particular circumstances, other areas that you
                can trim likely exist.
                The key to finding these areas is through tools and methods
                described here combined with experimentation and iteration.
                Here are a couple of areas to experiment with:
                <itemizedlist>
                    <listitem><para><filename>eglibc</filename>:
                        In general, follow this process:
                        <orderedlist>
                            <listitem><para>Remove <filename>eglibc</filename>
                                features from
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></ulink>
                                that you think you do not need.</para></listitem>
                            <listitem><para>Build your distribution.
                                </para></listitem>
                            <listitem><para>If the build fails due to missing
                                symbols in a package, determine if you can
                                reconfigure the package to not need those
                                features.
                                For example, change the configuration to not
                                support wide character support as is done for
                                <filename>ncurses</filename>.
                                Or, if support for those characters is needed,
                                determine what <filename>eglibc</filename>
                                features provide the support and restore the
                                configuration.
                                </para></listitem>
                            <listitem><para>Rebuild and repeat the process.
                                </para></listitem>
                        </orderedlist></para></listitem>
                    <listitem><para><filename>busybox</filename>:
                        For BusyBox, use a process similar as described for
                        <filename>eglibc</filename>.
                        A difference is you will need to boot the resulting
                        system to see if you are able to do everything you
                        expect from the running system.
                        You need to be sure to integrate configuration fragments
                        into Busybox because BusyBox handles its own core
                        features and then allows you to add configuration
                        fragments on top.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='iterate-on-the-process'>
            <title>Iterate on the Process</title>

            <para>
                If you have not reached your goals on system size, you need
                to iterate on the process.
                The process is the same.
                Use the tools and see just what is taking up 90% of the root
                filesystem and the kernel.
                Decide what you can eliminate without limiting your device
                beyond what you need.
            </para>

            <para>
                Depending on your system, a good place to look might be
                Busybox, which provides a stripped down
                version of Unix tools in a single, executable file.
                You might be able to drop virtual terminal services or perhaps
                ipv6.
            </para>
        </section>
    </section>

    <section id='working-with-packages'>
        <title>Working with Packages</title>

        <para>
            This section describes a few tasks that involve packages:
            <itemizedlist>
                <listitem><para>
                    <link linkend='excluding-packages-from-an-image'>Excluding packages from an image</link>
                    </para></listitem>
                <listitem><para>
                    <link linkend='incrementing-a-package-revision-number'>Incrementing a package revision number</link>
                    </para></listitem>
                <listitem><para>
                    <link linkend='usingpoky-configuring-DISTRO_PN_ALIAS'>Handling a package name alias</link>
                    </para></listitem>
                <listitem><para>
                    <link linkend='handling-optional-module-packaging'>Handling optional module packaging</link>
                    </para></listitem>
                <listitem><para>
                    <link linkend='using-runtime-package-management'>Using Runtime Package Management</link>
                    </para></listitem>
                <listitem><para>
                    <link linkend='testing-packages-with-ptest'>Setting up and running package test (ptest)</link>
                    </para></listitem>
            </itemizedlist>
        </para>

        <section id='excluding-packages-from-an-image'>
            <title>Excluding Packages from an Image</title>

            <para>
                You might find it necessary to prevent specific packages
                from being installed into an image.
                If so, you can use several variables to direct the build
                system to essentially ignore installing recommended packages
                or to not install a package at all.
            </para>

            <para>
                The following list introduces variables you can use to
                prevent packages from being installed into your image.
                Each of these variables only works with IPK and RPM
                package types.
                Support for Debian packages does not exist.
                Also, you can use these variables from your
                <filename>local.conf</filename> file or attach them to a
                specific image recipe by using a recipe name override.
                For more detail on the variables, see the descriptions in the
                Yocto Project Reference Manual's glossary chapter.
                <itemizedlist>
                    <listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-BAD_RECOMMENDATIONS'><filename>BAD_RECOMMENDATIONS</filename></ulink>:
                        Use this variable to specify "recommended-only"
                        packages that you do not want installed.
                        </para></listitem>
                    <listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-NO_RECOMMENDATIONS'><filename>NO_RECOMMENDATIONS</filename></ulink>:
                        Use this variable to prevent all "recommended-only"
                        packages from being installed.
                        </para></listitem>
                    <listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_EXCLUDE'><filename>PACKAGE_EXCLUDE</filename></ulink>:
                        Use this variable to prevent specific packages from
                        being installed regardless of whether they are
                        "recommended-only" or not.
                        You need to realize that the build process could
                        fail with an error when you
                        prevent the installation of a package whose presence
                        is required by an installed package.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='incrementing-a-package-revision-number'>
            <title>Incrementing a Package Revision Number</title>

            <para>
                If a committed change results in changing the package output,
                then the value of the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>
                variable needs to be increased (or "bumped").
                Increasing <filename>PR</filename> occurs one of two ways:
                <itemizedlist>
                    <listitem><para>Automatically using a Package Revision
                        Service (PR Service).</para></listitem>
                    <listitem><para>Manually incrementing the
                        <filename>PR</filename> variable.</para></listitem>
                </itemizedlist>
            </para>

            <para>
                Given that one of the challenges any build system and its
                users face is how to maintain a package feed that is compatible
                with existing package manager applications such as
                RPM, APT, and OPKG, using an automated system is much
                preferred over a manual system.
                In either system, the main requirement is that version
                numbering increases in a linear fashion and that a number of
                version components exist that support that linear progression.
            </para>

            <para>
                The following two sections provide information on the PR Service
                and on manual <filename>PR</filename> bumping.
            </para>

            <section id='working-with-a-pr-service'>
                <title>Working With a PR Service</title>

                <para>
                    As mentioned, attempting to maintain revision numbers in the
                    <ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink>
                    is error prone, inaccurate, and causes problems for people
                    submitting recipes.
                    Conversely, the PR Service automatically generates
                    increasing numbers, particularly the revision field,
                    which removes the human element.
                    <note>
                        For additional information on using a PR Service, you
                        can see the
                        <ulink url='&YOCTO_WIKI_URL;/wiki/PR_Service'>PR Service</ulink>
                        wiki page.
                    </note>
                </para>

                <para>
                    The Yocto Project uses variables in order of
                    decreasing priority to facilitate revision numbering (i.e.
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PE'><filename>PE</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>, and
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>
                    for epoch, version, and revision, respectively).
                    The values are highly dependent on the policies and
                    procedures of a given distribution and package feed.
                </para>

                <para>
                    Because the OpenEmbedded build system uses
                    "<ulink url='&YOCTO_DOCS_REF_URL;#checksums'>signatures</ulink>",
                    which are unique to a given build, the build system
                    knows when to rebuild packages.
                    All the inputs into a given task are represented by a
                    signature, which can trigger a rebuild when different.
                    Thus, the build system itself does not rely on the
                    <filename>PR</filename> numbers to trigger a rebuild.
                    The signatures, however, can be used to generate
                    <filename>PR</filename> values.
                </para>

                <para>
                    The PR Service works with both
                    <filename>OEBasic</filename> and
                    <filename>OEBasicHash</filename> generators.
                    The value of <filename>PR</filename> bumps when the
                    checksum changes and the different generator mechanisms
                    change signatures under different circumstances.
                </para>

                <para>
                    As implemented, the build system includes values from
                    the PR Service into the <filename>PR</filename> field as
                    an addition using the form "<filename>.x</filename>" so
                    <filename>r0</filename> becomes <filename>r0.1</filename>,
                    <filename>r0.2</filename> and so forth.
                    This scheme allows existing <filename>PR</filename> values
                    to be used for whatever reasons, which include manual
                    <filename>PR</filename> bumps, should it be necessary.
                </para>

                <para>
                    By default, the PR Service is not enabled or running.
                    Thus, the packages generated are just "self consistent".
                    The build system adds and removes packages and
                    there are no guarantees about upgrade paths but images
                    will be consistent and correct with the latest changes.
                </para>

                <para>
                    The simplest form for a PR Service is for it to exist
                    for a single host development system that builds the
                    package feed (building system).
                    For this scenario, you can enable a local PR Service by
                    setting
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PRSERV_HOST'><filename>PRSERV_HOST</filename></ulink>
                    in your <filename>local.conf</filename> file in the
                    <ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>:
                    <literallayout class='monospaced'>
     PRSERV_HOST = "localhost:0"
                    </literallayout>
                    Once the service is started, packages will automatically
                    get increasing <filename>PR</filename> values and
                    BitBake will take care of starting and stopping the server.
                </para>

                <para>
                    If you have a more complex setup where multiple host
                    development systems work against a common, shared package
                    feed, you have a single PR Service running and it is
                    connected to each building system.
                    For this scenario, you need to start the PR Service using
                    the <filename>bitbake-prserv</filename> command:
                    <literallayout class='monospaced'>
     bitbake-prserv &dash;&dash;host &lt;ip&gt; &dash;&dash;port &lt;port&gt; &dash;&dash;start
                    </literallayout>
                    In addition to hand-starting the service, you need to
                    update the <filename>local.conf</filename> file of each
                    building system as described earlier so each system
                    points to the server and port.
                </para>

                <para>
                    It is also recommended you use build history, which adds
                    some sanity checks to package versions, in conjunction with
                    the server that is running the PR Service.
                    To enable build history, add the following to each building
                    system's <filename>local.conf</filename> file:
                    <literallayout class='monospaced'>
     # It is recommended to activate "buildhistory" for testing the PR service
     INHERIT += "buildhistory"
     BUILDHISTORY_COMMIT = "1"
                    </literallayout>
                    For information on build history, see the
                    "<ulink url='&YOCTO_DOCS_REF_URL;#maintaining-build-output-quality'>Maintaining Build Output Quality</ulink>"
                    section in the Yocto Project Reference Manual.
                </para>

                <note>
                    <para>The OpenEmbedded build system does not maintain
                    <filename>PR</filename> information as part of the
                    shared state (sstate) packages.
                    If you maintain an sstate feed, its expected that either
                    all your building systems that contribute to the sstate
                    feed use a shared PR Service, or you do not run a PR
                    Service on any of your building systems.
                    Having some systems use a PR Service while others do
                    not leads to obvious problems.</para>
                    <para>For more information on shared state, see the
                    "<ulink url='&YOCTO_DOCS_REF_URL;#shared-state-cache'>Shared State Cache</ulink>"
                    section in the Yocto Project Reference Manual.</para>
                </note>
            </section>

            <section id='manually-bumping-pr'>
                <title>Manually Bumping PR</title>

                <para>
                    The alternative to setting up a PR Service is to manually
                    bump the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>
                    variable.
                </para>

                <para>
                    If a committed change results in changing the package output,
                    then the value of the PR variable needs to be increased
                    (or "bumped") as part of that commit.
                    For new recipes you should add the <filename>PR</filename>
                    variable and set its initial value equal to "r0", which is the default.
                    Even though the default value is "r0", the practice of adding it to a new recipe makes
                    it harder to forget to bump the variable when you make changes
                    to the recipe in future.
                </para>

                <para>
                    If you are sharing a common <filename>.inc</filename> file with multiple recipes,
                    you can also use the
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-INC_PR'>INC_PR</ulink></filename>
                    variable to ensure that
                    the recipes sharing the <filename>.inc</filename> file are rebuilt when the
                    <filename>.inc</filename> file itself is changed.
                    The <filename>.inc</filename> file must set <filename>INC_PR</filename>
                    (initially to "r0"), and all recipes referring to it should set <filename>PR</filename>
                    to "$(INC_PR).0" initially, incrementing the last number when the recipe is changed.
                    If the <filename>.inc</filename> file is changed then its
                    <filename>INC_PR</filename> should be incremented.
                </para>

                <para>
                    When upgrading the version of a package, assuming the
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PV'>PV</ulink></filename>
                    changes, the <filename>PR</filename> variable should be
                    reset to "r0" (or "$(INC_PR).0" if you are using
                    <filename>INC_PR</filename>).
                </para>

                <para>
                    Usually, version increases occur only to packages.
                    However, if for some reason <filename>PV</filename> changes but does not
                    increase, you can increase the
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PE'>PE</ulink></filename>
                    variable (Package Epoch).
                    The <filename>PE</filename> variable defaults to "0".
                </para>

                <para>
                    Version numbering strives to follow the
                    <ulink url='http://www.debian.org/doc/debian-policy/ch-controlfields.html'>
                    Debian Version Field Policy Guidelines</ulink>.
                    These guidelines define how versions are compared and what "increasing" a version means.
                </para>
            </section>
        </section>

        <section id="usingpoky-configuring-DISTRO_PN_ALIAS">
            <title>Handling a Package Name Alias</title>
            <para>
                Sometimes a package name you are using might exist under an alias or as a similarly named
                package in a different distribution.
                The OpenEmbedded build system implements a <filename>distro_check</filename>
                task that automatically connects to major distributions
                and checks for these situations.
                If the package exists under a different name in a different distribution, you get a
                <filename>distro_check</filename> mismatch.
                You can resolve this problem by defining a per-distro recipe name alias using the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_PN_ALIAS'>DISTRO_PN_ALIAS</ulink></filename>
                variable.
            </para>

            <para>
                Following is an example that shows how you specify the <filename>DISTRO_PN_ALIAS</filename>
                variable:
                <literallayout class='monospaced'>
     DISTRO_PN_ALIAS_pn-PACKAGENAME = "distro1=package_name_alias1 \
                                       distro2=package_name_alias2 \
                                       distro3=package_name_alias3 \
                                       ..."
                </literallayout>
            </para>

            <para>
                If you have more than one distribution alias, separate them with a space.
                Note that the build system currently automatically checks the
                Fedora, OpenSUSE, Debian, Ubuntu,
                and Mandriva distributions for source package recipes without having to specify them
                using the <filename>DISTRO_PN_ALIAS</filename> variable.
                For example, the following command generates a report that lists the Linux distributions
                that include the sources for each of the recipes.
                <literallayout class='monospaced'>
     $ bitbake world -f -c distro_check
                </literallayout>
                The results are stored in the <filename>build/tmp/log/distro_check-${DATETIME}.results</filename>
                file found in the
                <link linkend='source-directory'>Source Directory</link>.
            </para>
        </section>

        <section id='handling-optional-module-packaging'>
            <title>Handling Optional Module Packaging</title>

            <para>
                Many pieces of software split functionality into optional
                modules (or plug-ins) and the plug-ins that are built
                might depend on configuration options.
                To avoid having to duplicate the logic that determines what
                modules are available in your recipe or to avoid having
                to package each module by hand, the OpenEmbedded build system
                provides functionality to handle module packaging dynamically.
            </para>

            <para>
                To handle optional module packaging, you need to do two things:
                <itemizedlist>
                    <listitem><para>Ensure the module packaging is actually
                        done.</para></listitem>
                    <listitem><para>Ensure that any dependencies on optional
                        modules from other recipes are satisfied by your recipe.
                        </para></listitem>
                </itemizedlist>
            </para>

            <section id='making-sure-the-packaging-is-done'>
                <title>Making Sure the Packaging is Done</title>

                <para>
                    To ensure the module packaging actually gets done, you use
                    the <filename>do_split_packages</filename> function within
                    the <filename>populate_packages</filename> Python function
                    in your recipe.
                    The <filename>do_split_packages</filename> function
                    searches for a pattern of files or directories under a
                    specified path and creates a package for each one it finds
                    by appending to the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>
                    variable and setting the appropriate values for
                    <filename>FILES_packagename</filename>,
                    <filename>RDEPENDS_packagename</filename>,
                    <filename>DESCRIPTION_packagename</filename>, and so forth.
                    Here is an example from the <filename>lighttpd</filename>
                    recipe:
                    <literallayout class='monospaced'>
     python populate_packages_prepend () {
         lighttpd_libdir = d.expand('${libdir}')
         do_split_packages(d, lighttpd_libdir, '^mod_(.*)\.so$',
                          'lighttpd-module-%s', 'Lighttpd module for %s',
                           extra_depends='')
     }
                    </literallayout>
                    The previous example specifies a number of things in the
                    call to <filename>do_split_packages</filename>.
                    <itemizedlist>
                        <listitem><para>A directory within the files installed
                            by your recipe through <filename>do_install</filename>
                            in which to search.</para></listitem>
                        <listitem><para>A regular expression used to match module
                            files in that directory.
                            In the example, note the parentheses () that mark
                            the part of the expression from which the module
                            name should be derived.</para></listitem>
                        <listitem><para>A pattern to use for the package names.
                            </para></listitem>
                        <listitem><para>A description for each package.
                            </para></listitem>
                        <listitem><para>An empty string for
                            <filename>extra_depends</filename>, which disables
                            the default dependency on the main
                            <filename>lighttpd</filename> package.
                            Thus, if a file in <filename>${libdir}</filename>
                            called <filename>mod_alias.so</filename> is found,
                            a package called <filename>lighttpd-module-alias</filename>
                            is created for it and the
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-DESCRIPTION'><filename>DESCRIPTION</filename></ulink>
                            is set to "Lighttpd module for alias".</para></listitem>
                    </itemizedlist>
                </para>

                <para>
                    Often, packaging modules is as simple as the previous
                    example.
                    However, more advanced options exist that you can use
                    within <filename>do_split_packages</filename> to modify its
                    behavior.
                    And, if you need to, you can add more logic by specifying
                    a hook function that is called for each package.
                    It is also perfectly acceptable to call
                    <filename>do_split_packages</filename> multiple times if
                    you have more than one set of modules to package.
                </para>

                <para>
                    For more examples that show how to use
                    <filename>do_split_packages</filename>, see the
                    <filename>connman.inc</filename> file in the
                    <filename>meta/recipes-connectivity/connman/</filename>
                    directory of the <filename>poky</filename>
                    <link linkend='yocto-project-repositories'>source repository</link>.
                    You can also find examples in
                    <filename>meta/classes/kernel.bbclass</filename>.
                 </para>

                 <para>
                     Following is a reference that shows
                     <filename>do_split_packages</filename> mandatory and
                     optional arguments:
                     <literallayout class='monospaced'>
     Mandatory arguments

     root
        The path in which to search
     file_regex
        Regular expression to match searched files.
        Use parentheses () to mark the part of this
        expression that should be used to derive the
        module name (to be substituted where %s is
        used in other function arguments as noted below)
     output_pattern
        Pattern to use for the package names. Must
        include %s.
     description
        Description to set for each package. Must
        include %s.

     Optional arguments

     postinst
        Postinstall script to use for all packages
        (as a string)
     recursive
        True to perform a recursive search - default
        False
     hook
        A hook function to be called for every match.
        The function will be called with the following
        arguments (in the order listed):

        f
           Full path to the file/directory match
        pkg
           The package name
        file_regex
           As above
        output_pattern
           As above
        modulename
           The module name derived using file_regex

     extra_depends
        Extra runtime dependencies (RDEPENDS) to be
        set for all packages. The default value of None
        causes a dependency on the main package
        (${PN}) - if you do not want this, pass empty
        string '' for this parameter.
     aux_files_pattern
        Extra item(s) to be added to FILES for each
        package. Can be a single string item or a list
        of strings for multiple items. Must include %s.
     postrm
        postrm script to use for all packages (as a
        string)
     allow_dirs
        True to allow directories to be matched -
        default False
     prepend
        If True, prepend created packages to PACKAGES
        instead of the default False which appends them
     match_path
        match file_regex on the whole relative path to
        the root rather than just the file name
     aux_files_pattern_verbatim
        Extra item(s) to be added to FILES for each
        package, using the actual derived module name
        rather than converting it to something legal
        for a package name. Can be a single string item
        or a list of strings for multiple items. Must
        include %s.
     allow_links
        True to allow symlinks to be matched - default
        False
     summary
        Summary to set for each package. Must include %s;
        defaults to description if not set.
                     </literallayout>
                 </para>
            </section>

            <section id='satisfying-dependencies'>
                <title>Satisfying Dependencies</title>

                <para>
                    The second part for handling optional module packaging
                    is to ensure that any dependencies on optional modules
                    from other recipes are satisfied by your recipe.
                    You can be sure these dependencies are satisfied by
                    using the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES_DYNAMIC'><filename>PACKAGES_DYNAMIC</filename></ulink> variable.
                    Here is an example that continues with the
                    <filename>lighttpd</filename> recipe shown earlier:
                    <literallayout class='monospaced'>
     PACKAGES_DYNAMIC = "lighttpd-module-.*"
                    </literallayout>
                    The name specified in the regular expression can of
                    course be anything.
                    In this example, it is <filename>lighttpd-module-</filename>
                    and is specified as the prefix to ensure that any
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>
                    and <ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'><filename>RRECOMMENDS</filename></ulink>
                    on a package name starting with the prefix are satisfied
                    during build time.
                    If you are using <filename>do_split_packages</filename>
                    as described in the previous section, the value you put in
                    <filename>PACKAGES_DYNAMIC</filename> should correspond to
                    the name pattern specified in the call to
                    <filename>do_split_packages</filename>.
                </para>
            </section>
        </section>

        <section id='using-runtime-package-management'>
            <title>Using Runtime Package Management</title>

            <para>
                During a build, BitBake always transforms a recipe into one or
                more packages.
                For example, BitBake takes the <filename>bash</filename> recipe
                and currently produces the <filename>bash-dbg</filename>,
                <filename>bash-staticdev</filename>,
                <filename>bash-dev</filename>, <filename>bash-doc</filename>,
                <filename>bash-locale</filename>, and
                <filename>bash</filename> packages.
                Not all generated packages are included in an image.
            </para>

            <para>
                In several situations, you might need to update, add, remove,
                or query the packages on a target device at runtime
                (i.e. without having to generate a new image).
                Examples of such situations include:
                <itemizedlist>
                    <listitem><para>
                        You want to provide in-the-field updates to deployed
                        devices (e.g. security updates).
                        </para></listitem>
                    <listitem><para>
                        You want to have a fast turn-around development cycle
                        for one or more applications that run on your device.
                        </para></listitem>
                    <listitem><para>
                        You want to temporarily install the "debug" packages
                        of various applications on your device so that
                        debugging can be greatly improved by allowing
                        access to symbols and source debugging.
                        </para></listitem>
                    <listitem><para>
                        You want to deploy a more minimal package selection of
                        your device but allow in-the-field updates to add a
                        larger selection for customization.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                In all these situations, you have something similar to a more
                traditional Linux distribution in that in-field devices
                are able to receive pre-compiled packages from a server for
                installation or update.
                Being able to install these packages on a running,
                in-field device is what is termed "runtime package
                management".
            </para>

            <para>
                In order to use runtime package management, you
                need a host/server machine that serves up the pre-compiled
                packages plus the required metadata.
                You also need package manipulation tools on the target.
                The build machine is a likely candidate to act as the server.
                However, that machine does not necessarily have to be the
                package server.
                The build machine could push its artifacts to another machine
                that acts as the server (e.g. Internet-facing).
            </para>

            <para>
                A simple build that targets just one device produces
                more than one package database.
                In other words, the packages produced by a build are separated
                out into a couple of different package groupings based on
                criteria such as the target's CPU architecture, the target
                board, or the C library used on the target.
                For example, a build targeting the <filename>qemuarm</filename>
                device produces the following three package databases:
                <filename>all</filename>, <filename>armv5te</filename>, and
                <filename>qemuarm</filename>.
                If you wanted your <filename>qemuarm</filename> device to be
                aware of all the packages that were available to it,
                you would need to point it to each of these databases
                individually.
                In a similar way, a traditional Linux distribution usually is
                configured to be aware of a number of software repositories
                from which it retrieves packages.
            </para>

            <para>
                Using runtime package management is completely optional and
                not required for a successful build or deployment in any
                way.
                But if you want to make use of runtime package management,
                you need to do a couple things above and beyond the basics.
                The remainder of this section describes what you need to do.
            </para>

            <section id='runtime-package-management-build'>
                <title>Build Considerations</title>

                <para>
                    This section describes build considerations that you need
                    to be aware of in order to provide support for runtime
                    package management.
                </para>

                <para>
                    When BitBake generates packages it needs to know
                    what format or formats to use.
                    In your configuration, you use the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_CLASSES'><filename>PACKAGE_CLASSES</filename></ulink>
                    variable to specify the format.
                    <note>
                        You can choose to have more than one format but you must
                        provide at least one.
                    </note>
                </para>

                <para>
                    If you would like your image to start off with a basic
                    package database of the packages in your current build
                    as well as have the relevant tools available on the
                    target for runtime package management, you can include
                    "package-management" in the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
                    variable.
                    Including "package-management" in this
                    configuration variable ensures that when the image
                    is assembled for your target, the image includes
                    the currently-known package databases as well as
                    the target-specific tools required for runtime
                    package management to be performed on the target.
                    However, this is not strictly necessary.
                    You could start your image off without any databases
                    but only include the required on-target package
                    tool(s).
                    As an example, you could include "opkg" in your
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'><filename>IMAGE_INSTALL</filename></ulink>
                    variable if you are using the IPK package format.
                    You can then initialize your target's package database(s)
                    later once your image is up and running.
                </para>

                <para>
                    Whenever you perform any sort of build step that can
                    potentially generate a package or modify an existing
                    package, it is always a good idea to re-generate the
                    package index with:
                    <literallayout class='monospaced'>
    $ bitbake package-index
                    </literallayout>
                    Realize that it is not sufficient to simply do the
                    following:
                    <literallayout class='monospaced'>
    $ bitbake &lt;some-package&gt; package-index
                    </literallayout>
                    This is because BitBake does not properly schedule the
                    <filename>package-index</filename> target fully after any
                    other target has completed.
                    Thus, be sure to run the package update step separately.
                </para>

                <para>
                    As described below in the
                    "<link linkend='runtime-package-management-target-ipk'>Using IPK</link>"
                    section, if you are using IPK as your package format, you
                    can make use of the
                    <filename>distro-feed-configs</filename> recipe provided
                    by <filename>meta-oe</filename> in order to configure your
                    target to use your IPK databases.
                </para>

                <para>
                    When your build is complete, your packages reside in the
                    <filename>${TMPDIR}/deploy/&lt;package-format&gt;</filename>
                    directory.
                    For example, if <filename>${TMPDIR}</filename>
                    is <filename>tmp</filename> and your selected package type
                    is IPK, then your IPK packages are available in
                    <filename>tmp/deploy/ipk</filename>.
                </para>
            </section>

            <section id='runtime-package-management-server'>
                <title>Host or Server Machine Setup</title>

                <para>
                    Typically, packages are served from a server using
                    HTTP.
                    However, other protocols are possible.
                    If you want to use HTTP, then setup and configure a
                    web server, such as Apache 2 or lighttpd, on the machine
                    serving the packages.
                </para>

                <para>
                    As previously mentioned, the build machine can act as the
                    package server.
                    In the following sections that describe server machine
                    setups, the build machine is assumed to also be the server.
                </para>

                <section id='package-server-apache'>
                    <title>Serving Packages via Apache 2</title>

                    <para>
                        This example assumes you are using the Apache 2
                        server:
                        <orderedlist>
                            <listitem><para>
                                Add the directory to your Apache
                                configuration, which you can find at
                                <filename>/etc/httpd/conf/httpd.conf</filename>.
                                Use commands similar to these on the
                                development system.
                                These example commands assume a top-level
                                <link linkend='source-directory'>Source Directory</link>
                                named <filename>poky</filename> in your home
                                directory.
                                The example also assumes an RPM package type.
                                If you are using a different package type, such
                                as IPK, use "ipk" in the pathnames:
                                <literallayout class='monospaced'>
     &lt;VirtualHost *:80&gt;
       ....
         Alias /rpm ~/poky/build/tmp/deploy/rpm
         &lt;Directory "~/poky/build/tmp/deploy/rpm"&gt;
           Options +Indexes
         &lt;/Directory&gt;
     &lt;/VirtualHost&gt;
                                </literallayout></para></listitem>
                            <listitem><para>
                                Reload the Apache configuration as described
                                in this step.
                                For all commands, be sure you have root
                                privileges.
                                </para>

                                <para>
                                If your development system is using Fedora or
                                CentOS, use the following:
                                <literallayout class='monospaced'>
     # service httpd reload
                                </literallayout>
                                For Ubuntu and Debian, use the following:
                                <literallayout class='monospaced'>
     # /etc/init.d/apache2 reload
                                </literallayout>
                                For OpenSUSE, use the following:
                                <literallayout class='monospaced'>
     # /etc/init.d/apache2 reload
                                </literallayout></para></listitem>
                            <listitem><para>
                                If you are using Security-Enhanced Linux
                                (SELinux), you need to label the files as
                                being accessible through Apache.
                                Use the following command from the development
                                host.
                                This example assumes RPM package types:
                                <literallayout class='monospaced'>
     # chcon -R -h -t httpd_sys_content_t tmp/deploy/rpm
                                </literallayout></para></listitem>
                        </orderedlist>
                    </para>
                </section>

                <section id='package-server-lighttpd'>
                    <title>Serving Packages via lighttpd</title>

                    <para>
                        If you are using lighttpd, all you need
                        to do is to provide a link from your
                        <filename>${TMPDIR}/deploy/&lt;package-format&gt;</filename>
                        directory to lighttpd's document-root.
                        You can determine the specifics of your lighttpd
                        installation by looking through its configuration file,
                        which is usually found at:
                        <filename>/etc/lighttpd/lighttpd.conf</filename>.
                    </para>

                    <para>
                        For example, if you are using IPK, lighttpd's
                        document-root is set to
                        <filename>/var/www/lighttpd</filename>, and you had
                        packages for a target named "BOARD",
                        then you might create a link from your build location
                        to lighttpd's document-root as follows:
                        <literallayout class='monospaced'>
    # ln -s $(PWD)/tmp/deploy/ipk /var/www/lighttpd/BOARD-dir
                        </literallayout>
                    </para>

                    <para>
                        At this point, you need to start the lighttpd server.
                        The method used to start the server varies by
                        distribution.
                        However, one basic method that starts it by hand is:
                        <literallayout class='monospaced'>
    # lighttpd -f /etc/lighttpd/lighttpd.conf
                        </literallayout>
                    </para>
                </section>
            </section>

            <section id='runtime-package-management-target'>
                <title>Target Setup</title>

                <para>
                    Setting up the target differs depending on the
                    package management system.
                    This section provides information for RPM and IPK.
                </para>

                <section id='runtime-package-management-target-rpm'>
                    <title>Using RPM</title>

                    <para>
                        The application for performing runtime package
                        management of RPM packages on the target is called
                        <filename>smart</filename>.
                    </para>

                    <para>
                        On the target machine, you need to inform
                        <filename>smart</filename> of every package database
                        you want to use.
                        As an example, suppose your target device can use the
                        following three package databases from a server named
                        <filename>server.name</filename>:
                        <filename>all</filename>, <filename>i586</filename>,
                        and <filename>qemux86</filename>.
                        Given this example, issue the following commands on the
                        target:
                        <literallayout class='monospaced'>
     # smart channel --add all type=rpm-md baseurl=http://server.name/rpm/all
     # smart channel --add i585 type=rpm-md baseurl=http://server.name/rpm/i586
     # smart channel --add qemux86 type=rpm-md baseurl=http://server.name/rpm/qemux86
                        </literallayout>
                        Also from the target machine, fetch the repository
                        information using this command:
                        <literallayout class='monospaced'>
     # smart update
                        </literallayout>
                        You can now use the <filename>smart query</filename>
                        and <filename>smart install</filename> commands to
                        find and install packages from the repositories.
                    </para>
                </section>

                <section id='runtime-package-management-target-ipk'>
                    <title>Using IPK</title>

                    <para>
                        The application for performing runtime package
                        management of IPK packages on the target is called
                        <filename>opkg</filename>.
                    </para>

                    <para>
                        In order to inform <filename>opkg</filename> of the
                        package databases you want to use, simply create one
                        or more <filename>*.conf</filename> files in the
                        <filename>/etc/opkg</filename> directory on the target.
                        The <filename>opkg</filename> application uses them
                        to find its available package databases.
                        As an example, suppose you configured your HTTP server
                        on your machine named
                        <filename>www.mysite.com</filename> to serve files
                        from a <filename>BOARD-dir</filename> directory under
                        its document-root.
                        In this case, you might create a configuration
                        file on the target called
                        <filename>/etc/opkg/base-feeds.conf</filename> that
                        contains:
                        <literallayout class='monospaced'>
     src/gz all http://www.mysite.com/BOARD-dir/all
     src/gz armv7a http://www.mysite.com/BOARD-dir/armv7a
     src/gz beaglebone http://www.mysite.com/BOARD-dir/beaglebone
                        </literallayout>
                    </para>

                    <para>
                        As a way of making it easier to generate and make
                        these IPK configuration files available on your
                        target, simply define
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-FEED_DEPLOYDIR_BASE_URI'><filename>FEED_DEPLOYDIR_BASE_URI</filename></ulink>
                        to point to your server and the location within the
                        document-root which contains the databases.
                        For example: if you are serving your packages over
                        HTTP, your server's IP address is 192.168.7.1, and
                        your databases are located in a directory called
                        <filename>BOARD-dir</filename> underneath your HTTP
                        server's document-root, you need to set
                        <filename>FEED_DEPLOYDIR_BASE_URI</filename> to
                        <filename>http://192.168.7.1/BOARD-dir</filename> and
                        a set of configuration files will be generated for you
                        in your target to work with this feed.
                    </para>

                    <para>
                        On the target machine, fetch (or refresh) the
                        repository information using this command:
                        <literallayout class='monospaced'>
     # opkg update
                        </literallayout>
                        You can now use the <filename>opkg list</filename> and
                        <filename>opkg install</filename> commands to find and
                        install packages from the repositories.
                    </para>
                </section>
            </section>
        </section>

        <section id='testing-packages-with-ptest'>
            <title>Testing Packages With ptest</title>

            <para>
                A Package Test (ptest) runs tests against packages built
                by the OpenEmbedded build system on the target machine.
                A ptest contains at least two items: the actual test, and
                a shell script (<filename>run-ptest</filename>) that starts
                the test.
                The shell script that starts the test must not contain
                the actual test, the script only starts it.
                On the other hand, the test can be anything from a simple
                shell script that runs a binary and checks the output to
                an elaborate system of test binaries and data files.
            </para>

            <para>
                The test generates output in the format used by
                Automake:
                <literallayout class='monospaced'>
     &lt;result&gt;: &lt;testname&gt;
                </literallayout>
                where the result can be <filename>PASS</filename>,
                <filename>FAIL</filename>, or <filename>SKIP</filename>,
                and the testname can be any identifying string.
            </para>

            <note>
                A recipe is "ptest-enabled" if it inherits the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-ptest'><filename>ptest</filename></ulink>
                class.
            </note>

            <section id='adding-ptest-to-your-build'>
                <title>Adding ptest to Your Build</title>

                <para>
                    To add package testing to your build, add the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></ulink>
                    and <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_IMAGE_FEATURES'><filename>EXTRA_IMAGE_FEATURES</filename></ulink>
                    variables to your <filename>local.conf</filename> file,
                    which is found in the
                    <link linkend='build-directory'>Build Directory</link>:
                    <literallayout class='monospaced'>
     DISTRO_FEATURES_append = " ptest"
     EXTRA_IMAGE_FEATURES += "ptest-pkgs"
                    </literallayout>
                    Once your build is complete, the ptest files are installed
                    into the <filename>/usr/lib/&lt;package&gt;/ptest</filename>
                    directory within the image, where
                    <filename>&lt;package&gt;</filename> is the name of the
                    package.
                </para>
            </section>

            <section id='running-ptest'>
                <title>Running ptest</title>

                <para>
                    The <filename>ptest-runner</filename> package installs a
                    shell script that loops through all installed ptest test
                    suites and runs them in sequence.
                    Consequently, you might want to add this package to
                    your image.
                </para>
            </section>

            <section id='getting-your-package-ready'>
                <title>Getting Your Package Ready</title>

                <para>
                    In order to enable a recipe to run installed ptests
                    on target hardware,
                    you need to prepare the recipes that build the packages
                    you want to test.
                    Here is what you have to do for each recipe:
                    <itemizedlist>
                        <listitem><para><emphasis>Be sure the recipe
                            inherits the
                            <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-ptest'><filename>ptest</filename></ulink>
                            class:</emphasis>
                            Include the following line in each recipe:
                            <literallayout class='monospaced'>
     inherit ptest
                            </literallayout>
                            </para></listitem>
                        <listitem><para><emphasis>Create <filename>run-ptest</filename>:</emphasis>
                            This script starts your test.
                            Locate the script where you will refer to it
                            using
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>.
                            Here is an example that starts a test for
                            <filename>dbus</filename>:
                            <literallayout class='monospaced'>
     #!/bin/sh
     cd test
     make -k runtest-TESTS
                            </literallayout>
                            </para></listitem>
                        <listitem><para><emphasis>Ensure dependencies are
                            met:</emphasis>
                            If the test adds build or runtime dependencies
                            that normally do not exist for the package
                            (such as requiring "make" to run the test suite),
                            use the
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
                            and
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>
                            variables in your recipe in order for the package
                            to meet the dependencies.
                            Here is an example where the package has a runtime
                            dependency on "make":
                            <literallayout class='monospaced'>
     RDEPENDS_${PN}-ptest += "make"
                            </literallayout>
                            </para></listitem>
                        <listitem><para><emphasis>Add a function to build the
                            test suite:</emphasis>
                            Not many packages support cross-compilation of
                            their test suites.
                            Consequently, you usually need to add a
                            cross-compilation function to the package.
                            </para>
                            <para>Many packages based on Automake compile and
                            run the test suite by using a single command
                            such as <filename>make check</filename>.
                            However, the native <filename>make check</filename>
                            builds and runs on the same computer, while
                            cross-compiling requires that the package is built
                            on the host but executed on the target.
                            The built version of Automake that ships with the
                            Yocto Project includes a patch that separates
                            building and execution.
                            Consequently, packages that use the unaltered,
                            patched version of <filename>make check</filename>
                            automatically cross-compiles.</para>
                            <para>However, you still must add a
                            <filename>do_compile_ptest</filename> function to
                            build the test suite.
                            Add a function similar to the following to your
                            recipe:
                            <literallayout class='monospaced'>
     do_compile_ptest() {
        oe_runmake buildtest-TESTS
     }
                            </literallayout>
                            </para></listitem>
                       <listitem><para><emphasis>Ensure special configurations
                            are set:</emphasis>
                            If the package requires special configurations
                            prior to compiling the test code, you must
                            insert a <filename>do_configure_ptest</filename>
                            function into the recipe.
                            </para></listitem>
                       <listitem><para><emphasis>Install the test
                            suite:</emphasis>
                            The <filename>ptest</filename> class
                            automatically copies the file
                            <filename>run-ptest</filename> to the target and
                            then runs make <filename>install-ptest</filename>
                            to run the tests.
                            If this is not enough, you need to create a
                            <filename>do_install_ptest</filename> function and
                            make sure it gets called after the
                            "make install-ptest" completes.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>
        </section>
    </section>

    <section id="building-software-from-an-external-source">
        <title>Building Software from an External Source</title>

        <para>
            By default, the OpenEmbedded build system uses the
            <link linkend='build-directory'>Build Directory</link> to
            build source code.
            The build process involves fetching the source files, unpacking
            them, and then patching them if necessary before the build takes
            place.
        </para>

        <para>
            Situations exist where you might want to build software from source
            files that are external to and thus outside of the
            OpenEmbedded build system.
            For example, suppose you have a project that includes a new BSP with
            a heavily customized kernel.
            And, you want to minimize exposing the build system to the
            development team so that they can focus on their project and
            maintain everyone's workflow as much as possible.
            In this case, you want a kernel source directory on the development
            machine where the development occurs.
            You want the recipe's
            <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
            variable to point to the external directory and use it as is, not
            copy it.
        </para>

        <para>
            To build from software that comes from an external source, all you
            need to do is inherit the
            <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-externalsrc'><filename>externalsrc</filename></ulink>
            class and then set the
            <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTERNALSRC'><filename>EXTERNALSRC</filename></ulink>
            variable to point to your external source code.
            Here are the statements to put in your
            <filename>local.conf</filename> file:
            <literallayout class='monospaced'>
     INHERIT += "externalsrc"
     EXTERNALSRC_pn-myrecipe = "/some/path/to/your/source/tree"
            </literallayout>
        </para>

        <para>
            By default, <filename>externalsrc.bbclass</filename> builds
            the source code in a directory separate from the external source
            directory as specified by
            <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTERNALSRC'><filename>EXTERNALSRC</filename></ulink>.
            If you need to have the source built in the same directory in
            which it resides, or some other nominated directory, you can set
            <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTERNALSRC_BUILD'><filename>EXTERNALSRC_BUILD</filename></ulink>
            to point to that directory:
            <literallayout class='monospaced'>
     EXTERNALSRC_BUILD_pn-myrecipe = "/path/to/my/source/tree"
            </literallayout>
        </para>
    </section>

    <section id="selecting-an-initialization-manager">
        <title>Selecting an Initialization Manager</title>

        <para>
            By default, the Yocto Project uses SysVinit as the initialization
            manager.
            However, support also exists for systemd,
            which is a full replacement for init with
            parallel starting of services, reduced shell overhead and other
            features that are used by many distributions.
        </para>

        <para>
            If you want to use SysVinit, you do
            not have to do anything.
            But, if you want to use systemd, you must
            take some steps as described in the following sections.
        </para>

        <section id='using-systemd-exclusively'>
            <title>Using systemd Exclusively</title>

            <para>
                Set the these variables in your distribution configuration
                file as follows:
                <literallayout class='monospaced'>
     DISTRO_FEATURES_append = " systemd"
     VIRTUAL-RUNTIME_init_manager = "systemd"
                </literallayout>
                You can also prevent the SysVinit
                distribution feature from
                being automatically enabled as follows:
                <literallayout class='monospaced'>
     DISTRO_FEATURES_BACKFILL_CONSIDERED = "sysvinit"
                </literallayout>
                Doing so removes any redundant SysVinit scripts.
            </para>

            <para>
                To remove  initscripts from your image altogether,
                set this variable also:
                <literallayout class='monospaced'>
     VIRTUAL-RUNTIME_initscripts = ""
                </literallayout>
            </para>

            <para>
                For information on the backfill variable, see
                <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES_BACKFILL_CONSIDERED'><filename>DISTRO_FEATURES_BACKFILL_CONSIDERED</filename></ulink>.
            </para>
        </section>

        <section id='using-systemd-for-the-main-image-and-using-sysvinit-for-the-rescue-image'>
            <title>Using systemd for the Main Image and Using SysVinit for the Rescue Image</title>

            <para>
                Set the these variables in your distribution configuration
                file as follows:
                <literallayout class='monospaced'>
     DISTRO_FEATURES_append = " systemd"
     VIRTUAL-RUNTIME_init_manager = "systemd"
                </literallayout>
                Doing so causes your main image to use the
                <filename>packagegroup-core-boot.bb</filename> recipe and
                systemd.
                The rescue/minimal image cannot use this package group.
                However, it can install SysVinit
                and the appropriate packages will have support for both
                systemd and SysVinit.
            </para>
        </section>
    </section>

    <section id="platdev-appdev-srcrev">
        <title>Using an External SCM</title>

        <para>
            If you're working on a recipe that pulls from an external Source
            Code Manager (SCM), it is possible to have the OpenEmbedded build
            system notice new recipe changes added to the SCM and then build
            the resulting packages that depend on the new recipes by using
            the latest versions.
            This only works for SCMs from which it is possible to get a
            sensible revision number for changes.
            Currently, you can do this with Apache Subversion (SVN), Git, and
            Bazaar (BZR) repositories.
        </para>

        <para>
            To enable this behavior, the
            <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
            of the recipe needs to reference
            <ulink url='&YOCTO_DOCS_REF_URL;#var-SRCPV'><filename>SRCPV</filename></ulink>.
            Here is an example:
            <literallayout class='monospaced'>
     PV = "1.2.3+git${SRCPV}
            </literallayout>
            Then, you can add the following to your
            <filename>local.conf</filename>:
            <literallayout class='monospaced'>
     SRCREV_pn-&lt;PN&gt; = "${AUTOREV}"
            </literallayout>
            <ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink>
            is the name of the recipe for which you want to enable automatic source
            revision updating.
        </para>

        <para>
            If you do not want to update your local configuration file, you can
            add the following directly to the recipe to finish enabling
            the feature:
            <literallayout class='monospaced'>
     SRCREV = "${AUTOREV}"
            </literallayout>
        </para>

        <para>
            The Yocto Project provides a distribution named
            <filename>poky-bleeding</filename>, whose configuration
            file contains the line:
            <literallayout class='monospaced'>
     require conf/distro/include/poky-floating-revisions.inc
            </literallayout>
            This line pulls in the listed include file that contains
            numerous lines of exactly that form:
            <literallayout class='monospaced'>
     SRCREV_pn-gconf-dbus ?= "${AUTOREV}"
     SRCREV_pn-matchbox-common ?= "${AUTOREV}"
     SRCREV_pn-matchbox-config-gtk ?= "${AUTOREV}"
     SRCREV_pn-matchbox-desktop ?= "${AUTOREV}"
     SRCREV_pn-matchbox-keyboard ?= "${AUTOREV}"
     SRCREV_pn-matchbox-panel ?= "${AUTOREV}"
     SRCREV_pn-matchbox-panel-2 ?= "${AUTOREV}"
     SRCREV_pn-matchbox-themes-extra ?= "${AUTOREV}"
     SRCREV_pn-matchbox-terminal ?= "${AUTOREV}"
     SRCREV_pn-matchbox-wm ?= "${AUTOREV}"
     SRCREV_pn-matchbox-wm-2 ?= "${AUTOREV}"
     SRCREV_pn-settings-daemon ?= "${AUTOREV}"
     SRCREV_pn-screenshot ?= "${AUTOREV}"
     SRCREV_pn-libfakekey ?= "${AUTOREV}"
     SRCREV_pn-oprofileui ?= "${AUTOREV}"
          .
          .
          .
            </literallayout>
            These lines allow you to experiment with building a
            distribution that tracks the latest development source
            for numerous packages.
            <note><title>Caution</title>
                The <filename>poky-bleeding</filename> distribution
                is not tested on a regular basis.
                Keep this in mind if you use it.
            </note>
        </para>
    </section>

    <section id='creating-a-read-only-root-filesystem'>
        <title>Creating a Read-Only Root Filesystem</title>

        <para>
            Suppose, for security reasons, you need to disable
            your target device's root filesystem's write permissions
            (i.e. you need a read-only root filesystem).
            Or, perhaps you are running the device's operating system
            from a read-only storage device.
            For either case, you can customize your image for
            that behavior.
        </para>

        <note>
            Supporting a read-only root filesystem requires that the system and
            applications do not try to write to the root filesystem.
            You must configure all parts of the target system to write
            elsewhere, or to gracefully fail in the event of attempting to
            write to the root filesystem.
        </note>

        <section id='creating-the-root-filesystem'>
            <title>Creating the Root Filesystem</title>

            <para>
                To create the read-only root filesystem, simply add the
                "read-only-rootfs" feature to your image.
                Using either of the following statements in your
                image recipe or from within the
                <filename>local.conf</filename> file found in the
                <link linkend='build-directory'>Build Directory</link>
                causes the build system to create a read-only root filesystem:
                <literallayout class='monospaced'>
     IMAGE_FEATURES = "read-only-rootfs"
                </literallayout>
                or
                <literallayout class='monospaced'>
     EXTRA_IMAGE_FEATURES += "read-only-rootfs"
                </literallayout>
            </para>

            <para>
                For more information on how to use these variables, see the
                "<link linkend='usingpoky-extend-customimage-imagefeatures'>Customizing Images Using Custom <filename>IMAGE_FEATURES</filename> and <filename>EXTRA_IMAGE_FEATURES</filename></link>"
                section.
                For information on the variables, see
                <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
                and <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_IMAGE_FEATURES'><filename>EXTRA_IMAGE_FEATURES</filename></ulink>.
            </para>
        </section>

        <section id='post-installation-scripts'>
            <title>Post-Installation Scripts</title>

            <para>
                It is very important that you make sure all
                post-Installation (<filename>pkg_postinst</filename>) scripts
                for packages that are installed into the image can be run
                at the time when the root filesystem is created during the
                build on the host system.
                These scripts cannot attempt to run during first-boot on the
                target device.
                With the "read-only-rootfs" feature enabled,
                the build system checks during root filesystem creation to make
                sure all post-installation scripts succeed.
                If any of these scripts still need to be run after the root
                filesystem is created, the build immediately fails.
                These build-time checks ensure that the build fails
                rather than the target device fails later during its
                initial boot operation.
            </para>

            <para>
                Most of the common post-installation scripts generated by the
                build system for the out-of-the-box Yocto Project are engineered
                so that they can run during root filesystem creation
                (e.g. post-installation scripts for caching fonts).
                However, if you create and add custom scripts, you need
                to be sure they can be run during this file system creation.
            </para>

            <para>
                Here are some common problems that prevent
                post-installation scripts from running during root filesystem
                creation:
                <itemizedlist>
                    <listitem><para>
                        <emphasis>Not using $D in front of absolute
                        paths:</emphasis>
                        The build system defines
                        <filename>$</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink>
                        when the root filesystem is created.
                        Furthermore, <filename>$D</filename> is blank when the
                        script is run on the target device.
                        This implies two purposes for <filename>$D</filename>:
                        ensuring paths are valid in both the host and target
                        environments, and checking to determine which
                        environment is being used as a method for taking
                        appropriate actions.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Attempting to run processes that are
                        specific to or dependent on the target
                        architecture:</emphasis>
                        You can work around these attempts by using native
                        tools to accomplish the same tasks, or
                        by alternatively running the processes under QEMU,
                        which has the <filename>qemu_run_binary</filename>
                        function.
                        For more information, see the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-qemu'><filename>qemu</filename></ulink>
                        class.</para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='areas-with-write-access'>
            <title>Areas With Write Access</title>

            <para>
                With the "read-only-rootfs" feature enabled,
                any attempt by the target to write to the root filesystem at
                runtime fails.
                Consequently, you must make sure that you configure processes
                and applications that attempt these types of writes do so
                to directories with write access (e.g.
                <filename>/tmp</filename> or <filename>/var/run</filename>).
            </para>
        </section>
    </section>

    <section id="performing-automated-runtime-testing">
        <title>Performing Automated Runtime Testing</title>

        <para>
            The OpenEmbedded build system makes available a series of automated
            tests for images to verify runtime functionality.
            You can run these tests on either QEMU or actual target hardware.
            Tests are written in Python making use of the
            <filename>unittest</filename> module, and the majority of them
            run commands on the target system over SSH.
            This section describes how you set up the environment to use these
            tests, run available tests, and write and add your own tests.
        </para>

        <section id='enabling-tests'>
            <title>Enabling Tests</title>

            <para>
                Depending on whether you are planning on running tests using
                QEMU or on running them on the hardware, you have to take
                different steps to enable the tests.
                See the following subsections for information on how to
                enable both types of tests.
            </para>

            <section id='qemu-image-enabling-tests'>
                <title>Enabling Runtime Tests on QEMU</title>

                <para>
                    In order to run tests, you need to do the following:
                    <itemizedlist>
                        <listitem><para><emphasis>Set up to avoid interaction
                            with <filename>sudo</filename> for networking:</emphasis>
                            To accomplish this, you must do one of the
                            following:
                            <itemizedlist>
                                <listitem><para>Add
                                    <filename>NOPASSWD</filename> for your user
                                    in <filename>/etc/sudoers</filename> either for
                                    ALL commands or just for
                                    <filename>runqemu-ifup</filename>.
                                    You must provide the full path as that can
                                    change if you are using multiple clones of the
                                    source repository.
                                    <note>
                                        On some distributions, you also need to
                                        comment out "Defaults requiretty" in
                                        <filename>/etc/sudoers</filename>.
                                    </note></para></listitem>
                                <listitem><para>Manually configure a tap interface
                                    for your system.</para></listitem>
                                <listitem><para>Run as root the script in
                                    <filename>scripts/runqemu-gen-tapdevs</filename>,
                                    which should generate a list of tap devices.
                                    This is the option typically chosen for
                                    Autobuilder-type environments.
                                    </para></listitem>
                            </itemizedlist></para></listitem>
                        <listitem><para><emphasis>Set the
                            <filename>DISPLAY</filename> variable:</emphasis>
                            You need to set this variable so that you have an X
                            server available (e.g. start
                            <filename>vncserver</filename> for a headless machine).
                            </para></listitem>
                        <listitem><para><emphasis>Be sure your host's firewall
                            accepts incoming connections from
                            192.168.7.0/24:</emphasis>
                            Some of the tests (in particular smart tests) start an
                            HTTP server on a random high number port, which is
                            used to serve files to the target.
                            The smart module serves
                            <filename>${DEPLOY_DIR}/rpm</filename> so it can run
                            smart channel commands. That means your host's firewall
                            must accept incoming connections from 192.168.7.0/24,
                            which is the default IP range used for tap devices
                            by <filename>runqemu</filename>.</para></listitem>
                    </itemizedlist>
                </para>

                <para>
                    Once you start running the tests, the following happens:
                    <itemizedlist>
                        <listitem><para>A copy of the root filesystem is written
                            to <filename>${WORKDIR}/testimage</filename>.
                            </para></listitem>
                        <listitem><para>The image is booted under QEMU using the
                            standard <filename>runqemu</filename> script.
                            </para></listitem>
                        <listitem><para>A default timeout of 500 seconds occurs
                            to allow for the boot process to reach the login prompt.
                            You can change the timeout period by setting
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-TEST_QEMUBOOT_TIMEOUT'><filename>TEST_QEMUBOOT_TIMEOUT</filename></ulink>
                            in the <filename>local.conf</filename> file.
                            </para></listitem>
                        <listitem><para>Once the boot process is reached and the
                            login prompt appears, the tests run.
                            The full boot log is written to
                            <filename>${WORKDIR}/testimage/qemu_boot_log</filename>.
                            </para></listitem>
                        <listitem><para>Each test module loads in the order found
                            in <filename>TEST_SUITES</filename>.
                            You can find the full output of the commands run over
                            SSH in
                            <filename>${WORKDIR}/testimgage/ssh_target_log</filename>.
                            </para></listitem>
                        <listitem><para>If no failures occur, the task running the
                            tests ends successfully.
                            You can find the output from the
                            <filename>unittest</filename> in the task log at
                            <filename>${WORKDIR}/temp/log.do_testimage</filename>.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>

            <section id='hardware-image-enabling-tests'>
                <title>Enabling Runtime Tests on Hardware</title>

                <para>
                    The OpenEmbedded build system can run tests on real
                    hardware, and for certain devices it can also deploy
                    the image to be tested onto the device beforehand.
                </para>

                <para>
                    For automated deployment, a "master image" is installed
                    onto the hardware once as part of setup.
                    Then, each time tests are to be run, the following
                    occurs:
                    <orderedlist>
                        <listitem><para>The master image is booted into and
                            used to write the image to be tested to
                            a second partition.
                            </para></listitem>
                        <listitem><para>The device is then rebooted using an
                            external script that you need to provide.
                            </para></listitem>
                        <listitem><para>The device boots into the image to be
                            tested.
                            </para></listitem>
                    </orderedlist>
                </para>

                <para>
                    When running tests (independent of whether the image
                    has been deployed automatically or not), the device is
                    expected to be connected to a network on a
                    pre-determined IP address.
                    You can either use static IP addresses written into
                    the image, or set the image to use DHCP and have your
                    DHCP server on the test network assign a known IP address
                    based on the MAC address of the device.
                </para>

                <para>
                    In order to run tests on hardware, you need to set
                    <filename>TEST_TARGET</filename> to an appropriate value.
                    For QEMU, you do not have to change anything, the default
                    value is "QemuTarget".
                    For running tests on hardware, two options exist:
                    "SimpleRemoteTarget" and "GummibootTarget".
                    <itemizedlist>
                        <listitem><para><emphasis>"SimpleRemoteTarget":</emphasis>
                            Choose "SimpleRemoteTarget" if you are going to
                            run tests on a target system that is already
                            running the image to be tested and is available
                            on the network.
                            You can use "SimpleRemoteTarget" in conjunction
                            with either real hardware or an image running
                            within a separately started QEMU or any
                            other virtual machine manager.
                            </para></listitem>
                        <listitem><para><emphasis>"GummibootTarget":</emphasis>
                            Choose "GummibootTarget" if your hardware is
                            an EFI-based machine with
                            <filename>gummiboot</filename> as bootloader and
                            <filename>core-image-testmaster</filename>
                            (or something similar) is installed.
                            Also, your hardware under test must be in a
                            DHCP-enabled network that gives it the same IP
                            address for each reboot.</para>
                            <para>If you choose "GummibootTarget", there are
                            additional requirements and considerations.
                            See the
                            "<link linkend='selecting-gummiboottarget'>Selecting GummibootTarget</link>"
                            section, which follows, for more information.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>

            <section id='selecting-gummiboottarget'>
                <title>Selecting GummibootTarget</title>

                <para>
                    If you did not set <filename>TEST_TARGET</filename> to
                    "GummibootTarget", then you do not need any information
                    in this section.
                    You can skip down to the
                    "<link linkend='qemu-image-running-tests'>Running Tests</link>"
                    section.
                </para>

                <para>
                    If you did set <filename>TEST_TARGET</filename> to
                    "GummibootTarget", you also need to perform a one-time
                    setup of your master image by doing the following:
                    <orderedlist>
                        <listitem><para><emphasis>Set <filename>EFI_PROVIDER</filename>:</emphasis>
                            Be sure that <filename>EFI_PROVIDER</filename>
                            is as follows:
                            <literallayout class='monospaced'>
     EFI_PROVIDER = "gummiboot"
                            </literallayout>
                            </para></listitem>
                        <listitem><para><emphasis>Build the master image:</emphasis>
                            Build the <filename>core-image-testmaster</filename>
                            image.
                            The <filename>core-image-testmaster</filename>
                            recipe is provided as an example for a
                            "master" image and you can customize the image
                            recipe as you would any other recipe.
                            </para>
                            <para>Here are the image recipe requirements:
                            <itemizedlist>
                                <listitem><para>Inherits
                                    <filename>core-image</filename>
                                    so that kernel modules are installed.
                                    </para></listitem>
                                <listitem><para>Installs normal linux utilities
                                    not busybox ones (e.g.
                                    <filename>bash</filename>,
                                    <filename>coreutils</filename>,
                                    <filename>tar</filename>,
                                    <filename>gzip</filename>, and
                                    <filename>kmod</filename>).
                                    </para></listitem>
                                <listitem><para>Uses a custom
                                    initramfs image with a custom installer.
                                    A normal image that you can install usually
                                    creates a single rootfs partition.
                                    This image uses another installer that
                                    creates a specific partition layout.
                                    Not all Board Support Packages (BSPs)
                                    can use an installer.
                                    For such cases, you need to manually create
                                    the following partition layout on the
                                    target:
                                    <itemizedlist>
                                        <listitem><para>First partition mounted
                                            under <filename>/boot</filename>,
                                            labeled "boot".
                                            </para></listitem>
                                        <listitem><para>The main rootfs
                                            partition where this image gets
                                            installed, which is mounted under
                                            <filename>/</filename>.
                                            </para></listitem>
                                        <listitem><para>Another partition
                                            labeled "testrootfs" where test
                                            images get deployed.
                                            </para></listitem>
                                    </itemizedlist>
                                    </para></listitem>
                            </itemizedlist>
                            </para></listitem>
                        <listitem><para><emphasis>Install image:</emphasis>
                            Install the image that you just built on the target
                            system.
                            </para></listitem>
                    </orderedlist>
                </para>

                <para>
                    The final thing you need to do when setting
                    <filename>TEST_TARGET</filename> to "GummibootTarget" is
                    to set up the test image:
                    <orderedlist>
                        <listitem><para><emphasis>Set up your <filename>local.conf</filename> file:</emphasis>
                            Make sure you have the following statements in
                            your <filename>local.conf</filename> file:
                            <literallayout class='monospaced'>
     IMAGE_FSTYPES += "tar.gz"
     INHERIT += "testimage"
     TEST_TARGET = "GummibootTarget"
     TEST_TARGET_IP = "192.168.2.3"
                            </literallayout>
                            </para></listitem>
                        <listitem><para><emphasis>Build your test image:</emphasis>
                            Use BitBake to build the image:
                            <literallayout class='monospaced'>
     $ bitbake core-image-sato
                            </literallayout>
                            </para></listitem>
                    </orderedlist>
                </para>

                <para>
                    Here is some additional information regarding running
                    "GummibootTarget" as your test target:
                    <itemizedlist>
                        <listitem><para>
                            You can use
                            <filename>TEST_POWERCONTROL_CMD</filename>
                            together with
                            <filename>TEST_POWERCONTROL_EXTRA_ARGS</filename>
                            as a command that runs on the host and does power
                            cycling.
                            The test code passes one argument to that command:
                            off, on or cycle (off then on).
                            Here is an example that could appear in your
                            <filename>local.conf</filename> file:
                            <literallayout class='monospaced'>
     TEST_POWERCONTROL_CMD = "powercontrol.exp test 10.11.12.1 nuc1"
                            </literallayout>
                            In this example, the expect script does the
                            following:
                            <literallayout class='monospaced'>
     ssh test@10.11.12.1 "pyctl nuc1 &lt;arg&gt;"
                            </literallayout>
                            It then runs a Python script that controls power
                            for a label called <filename>nuc1</filename>.
                            <note>
                                You need to customize
                                <filename>TEST_POWERCONTROL_CMD</filename>
                                and
                                <filename>TEST_POWERCONTROL_EXTRA_ARGS</filename>
                                for your own setup.
                                The one requirement is that it accepts
                                "on", "off", and "cycle" as the last argument.
                            </note>
                            </para></listitem>
                        <listitem><para>
                            When no command is defined, it connects to the
                            device over SSH and uses the classic reboot command
                            to reboot the device.
                            Classic reboot is fine as long as the machine
                            actually reboots (i.e. the SSH test has not
                            failed).
                            It is useful for scenarios where you have a simple
                            setup, typically with a single board, and where
                            some manual interaction is okay from time to time.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>
        </section>

        <section id="qemu-image-running-tests">
            <title>Running Tests</title>

            <para>
                You can start the tests automatically or manually:
                <itemizedlist>
                    <listitem><para><emphasis>Automatically running tests:</emphasis>
                        To run the tests automatically after the
                        OpenEmbedded build system successfully creates an image,
                        first set the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-TEST_IMAGE'><filename>TEST_IMAGE</filename></ulink>
                        variable to "1" in your <filename>local.conf</filename>
                        file in the
                        <ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>:
                        <literallayout class='monospaced'>
     TEST_IMAGE = "1"
                        </literallayout>
                        Next, build your image.
                        If the image successfully builds, the tests will be
                        run:
                        <literallayout class='monospaced'>
     bitbake core-image-sato
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Manually running tests:</emphasis>
                        To manually run the tests, first globally inherit the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-testimage'><filename>testimage</filename></ulink>
                        class by editing your <filename>local.conf</filename>
                        file:
                        <literallayout class='monospaced'>
    INHERIT += "testimage"
                        </literallayout>
                        Next, use BitBake to run the tests:
                        <literallayout class='monospaced'>
     bitbake -c testimage &lt;image&gt;
                        </literallayout></para></listitem>
                </itemizedlist>
            </para>

            <para>
                All test files reside in
                <filename>meta/lib/oeqa/runtime</filename> in the
                <link linkend='source-directory'>Source Directory</link>.
                A test name maps directly to a Python module.
                Each test module may contain a number of individual tests.
                Tests are usually grouped together by the area
                tested (e.g tests for systemd reside in
                <filename>meta/lib/oeqa/runtime/systemd.py</filename>).
            </para>

            <para>
                You can add tests to any layer provided you place them in the
                proper area and you extend
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BBPATH'><filename>BBPATH</filename></ulink>
                in the <filename>local.conf</filename> file as normal.
                Be sure that tests reside in
                <filename>&lt;layer&gt;/lib/oeqa/runtime</filename>.
                <note>
                    Be sure that module names do not collide with module names
                    used in the default set of test modules in
                    <filename>meta/lib/oeqa/runtime</filename>.
                </note>
            </para>

            <para>
                You can change the set of tests run by appending or overriding
                <ulink url='&YOCTO_DOCS_REF_URL;#var-TEST_SUITES'><filename>TEST_SUITES</filename></ulink>
                variable in <filename>local.conf</filename>.
                Each name in <filename>TEST_SUITES</filename> represents a
                required test for the image.
                Test modules named within <filename>TEST_SUITES</filename>
                cannot be skipped even if a test is not suitable for an image
                (e.g. running the RPM tests on an image without
                <filename>rpm</filename>).
                Appending "auto" to <filename>TEST_SUITES</filename> causes the
                build system to try to run all tests that are suitable for the
                image (i.e. each test module may elect to skip itself).
            </para>

            <para>
                The order you list tests in <filename>TEST_SUITES</filename>
                is important and influences test dependencies.
                Consequently, tests that depend on other tests should be added
                after the test on which they depend.
                For example, since the <filename>ssh</filename> test
                depends on the
                <filename>ping</filename> test, "ssh" needs to come after
                "ping" in the list.
                The test class provides no re-ordering or dependency handling.
                <note>
                    Each module can have multiple classes with multiple test
                    methods.
                    And, Python <filename>unittest</filename> rules apply.
                </note>
            </para>

            <para>
                Here are some things to keep in mind when running tests:
                <itemizedlist>
                    <listitem><para>The default tests for the image are defined
                        as:
                        <literallayout class='monospaced'>
     DEFAULT_TEST_SUITES_pn-&lt;image&gt; = "ping ssh df connman syslog xorg scp vnc date rpm smart dmesg"
                        </literallayout></para></listitem>
                    <listitem><para>Add your own test to the list of the
                        by using the following:
                        <literallayout class='monospaced'>
     TEST_SUITES_append = " mytest"
                        </literallayout></para></listitem>
                    <listitem><para>Run a specific list of tests as follows:
                        <literallayout class='monospaced'>
     TEST_SUITES = "test1 test2 test3"
                        </literallayout>
                        Remember, order is important.
                        Be sure to place a test that is dependent on another test
                        later in the order.</para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id="exporting-tests">
            <title>Exporting Tests</title>

            <para>
                You can export tests so that they can run independently of
                the build system.
                Exporting tests is required if you want to be able to hand
                the test execution off to a scheduler.
                You can only export tests that are defined in
                <ulink url='&YOCTO_DOCS_REF_URL;#var-TEST_SUITES'><filename>TEST_SUITES</filename></ulink>.
            </para>

            <para>
                If you image is already built, make sure the following are set
                in your <filename>local.conf</filename> file.
                Be sure to provide the IP address you need:
                <literallayout class='monospaced'>
     TEST_EXPORT_ONLY = "1"
     TEST_TARGET = "simpleremote"
     TEST_TARGET_IP = "192.168.7.2"
     TEST_SERVER_IP = "192.168.7.1"
                </literallayout>
                You can then export the tests with the following:
                <literallayout class='monospaced'>
     $ bitbake core-image-sato -c testimage
                </literallayout>
                Exporting the tests places them in the
                <link linkend='build-directory'>Build Directory</link> in
                <filename>tmp/testimage/core-image-sato</filename>, which
                is controlled by the
                <filename>TEST_EXPORT_DIR</filename> variable.
            </para>

            <para>
                The exported data (i.e. <filename>testdata.json</filename>)
                contains paths to the Build Directory.
                Thus, the contents of the directory can be moved
                to another machine as long as you update some paths in the
                JSON.
                Usually you only care about the
                ${DEPLOY_DIR}/rpm directory (assuming the RPM and Smart tests
                are enabled).
                Consequently, running the tests on other machine
                means that you have to move the contents and call
                <filename>runexported</filename> with "--deploy-dir PATH:
                ./runexported.py --deploy-dir /new/path/on/this/machine testdata.json
                runexported.py accepts other arguments as well, see --help.
            </para>

            <para>
                You can now run the tests outside of the build environment:
                <literallayout class='monospaced'>
     $ cd tmp/testimage/core-image-sato
     $ ./runexported.py testdata.json
                </literallayout>
                <note>
                    This "export" feature does not deploy or boot the target
                    image.
                    Your target (be it a Qemu or hardware one)
                    has to already be up and running when you call
                    <filename>runexported.py</filename>
                </note>
            </para>
        </section>

        <section id="qemu-image-writing-new-tests">
            <title>Writing New Tests</title>

            <para>
                As mentioned previously, all new test files need to be in the
                proper place for the build system to find them.
                New tests for additional functionality outside of the core
                should be added to the layer that adds the functionality, in
                <filename>&lt;layer&gt;/lib/oeqa/runtime</filename> (as
                long as
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BBPATH'><filename>BBPATH</filename></ulink>
                is extended in the layer's
                <filename>layer.conf</filename> file as normal).
                Just remember that filenames need to map directly to test
                (module) names and that you do not use module names that
                collide with existing core tests.
            </para>

            <para>
                To create a new test, start by copying an existing module
                (e.g. <filename>syslog.py</filename> or
                <filename>gcc.py</filename> are good ones to use).
                Test modules can use code from
                <filename>meta/lib/oeqa/utils</filename>, which are helper
                classes.
            </para>

            <note>
                Structure shell commands such that you rely on them and they
                return a single code for success.
                Be aware that sometimes you will need to parse the output.
                See the <filename>df.py</filename> and
                <filename>date.py</filename> modules for examples.
            </note>

            <para>
                You will notice that all test classes inherit
                <filename>oeRuntimeTest</filename>, which is found in
                <filename>meta/lib/oetest.py</filename>.
                This base class offers some helper attributes, which are
                described in the following sections:
            </para>

            <section id='qemu-image-writing-tests-class-methods'>
                <title>Class Methods</title>

                <para>
                    Class methods are as follows:
                    <itemizedlist>
                        <listitem><para><emphasis><filename>hasPackage(pkg)</filename>:</emphasis>
                            Returns "True" if <filename>pkg</filename> is in the
                            installed package list of the image, which is based
                            on the manifest file that is generated during the
                            <filename>do.rootfs</filename> task.
                            </para></listitem>
                        <listitem><para><emphasis><filename>hasFeature(feature)</filename>:</emphasis>
                            Returns "True" if the feature is in
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
                            or
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></ulink>.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>

            <section id='qemu-image-writing-tests-class-attributes'>
                <title>Class Attributes</title>

                <para>
                    Class attributes are as follows:
                    <itemizedlist>
                        <listitem><para><emphasis><filename>pscmd</filename>:</emphasis>
                            Equals "ps -ef" if <filename>procps</filename> is
                            installed in the image.
                            Otherwise, <filename>pscmd</filename> equals
                            "ps" (busybox).
                            </para></listitem>
                        <listitem><para><emphasis><filename>tc</filename>:</emphasis>
                            The called text context, which gives access to the
                            following attributes:
                            <itemizedlist>
                                <listitem><para><emphasis><filename>d</filename>:</emphasis>
                                    The BitBake datastore, which allows you to
                                    use stuff such as
                                    <filename>oeRuntimeTest.tc.d.getVar("VIRTUAL-RUNTIME_init_manager")</filename>.
                                    </para></listitem>
                                <listitem><para><emphasis><filename>testslist</filename> and <filename>testsrequired</filename>:</emphasis>
                                    Used internally.
                                    The tests do not need these.
                                    </para></listitem>
                                <listitem><para><emphasis><filename>filesdir</filename>:</emphasis>
                                    The absolute path to
                                    <filename>meta/lib/oeqa/runtime/files</filename>,
                                    which contains helper files for tests meant
                                    for copying on the target such as small
                                    files written in C for compilation.
                                    </para></listitem>
                                <listitem><para><emphasis><filename>target</filename>:</emphasis>
                                    The target controller object used to deploy
                                    and start an image on a particular target
                                    (e.g. QemuTarget, SimpleRemote, and
                                    GummibootTarget).
                                    Tests usually use the following:
                                    <itemizedlist>
                                        <listitem><para><emphasis><filename>ip</filename>:</emphasis>
                                            The target's IP address.
                                            </para></listitem>
                                        <listitem><para><emphasis><filename>server_ip</filename>:</emphasis>
                                            The host's IP address, which is
                                            usually used by the "smart" test
                                            suite.
                                            </para></listitem>
                                        <listitem><para><emphasis><filename>run(cmd, timeout=None)</filename>:</emphasis>
                                            The single, most used method.
                                            This command is a wrapper for:
                                            <filename>ssh root@host "cmd"</filename>.
                                            The command returns a tuple:
                                            (status, output), which are what
                                            their names imply - the return code
                                            of 'cmd' and whatever output
                                            it produces.
                                            The optional timeout argument
                                            represents the number of seconds the
                                            test should wait for 'cmd' to
                                            return.
                                            If the argument is "None", the
                                            test uses the default instance's
                                            timeout period, which is 300
                                            seconds.
                                            If the argument is "0", the test
                                            runs until the command returns.
                                            </para></listitem>
                                        <listitem><para><emphasis><filename>copy_to(localpath, remotepath)</filename>:</emphasis>
                                            <filename>scp localpath root@ip:remotepath</filename>.
                                            </para></listitem>
                                        <listitem><para><emphasis><filename>copy_from(remotepath, localpath)</filename>:</emphasis>
                                            <filename>scp root@host:remotepath localpath</filename>.
                                            </para></listitem>
                                    </itemizedlist></para></listitem>
                            </itemizedlist></para></listitem>
                    </itemizedlist>
                </para>
            </section>

            <section id='qemu-image-writing-tests-instance-attributes'>
                <title>Instance Attributes</title>

                <para>
                    A single instance attribute exists, which is
                    <filename>target</filename>.
                    The <filename>target</filename> instance attribute is
                    identical to the class attribute of the same name, which
                    is described in the previous section.
                    This attribute exists as both an instance and class
                    attribute so tests can use
                    <filename>self.target.run(cmd)</filename> in instance
                    methods instead of
                    <filename>oeRuntimeTest.tc.target.run(cmd)</filename>.
                </para>
            </section>
        </section>
    </section>

    <section id="platdev-gdb-remotedebug">
        <title>Debugging With the GNU Project Debugger (GDB) Remotely</title>

        <para>
            GDB allows you to examine running programs, which in turn helps you to understand and fix problems.
            It also allows you to perform post-mortem style analysis of program crashes.
            GDB is available as a package within the Yocto Project and is
            installed in SDK images by default.
            See the "<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>" chapter
            in the Yocto Project Reference Manual for a description of these images.
            You can find information on GDB at <ulink url="http://sourceware.org/gdb/"/>.
        </para>

        <tip>
            For best results, install DBG (<filename>-dbg</filename>) packages
            for the applications you are going to debug.
            Doing so makes extra debug symbols available that give you more
            meaningful output.
        </tip>

        <para>
            Sometimes, due to memory or disk space constraints, it is not possible
            to use GDB directly on the remote target to debug applications.
            These constraints arise because GDB needs to load the debugging information and the
            binaries of the process being debugged.
            Additionally, GDB needs to perform many computations to locate information such as function
            names, variable names and values, stack traces and so forth - even before starting the
            debugging process.
            These extra computations place more load on the target system and can alter the
            characteristics of the program being debugged.
        </para>

        <para>
            To help get past the previously mentioned constraints, you can use Gdbserver.
            Gdbserver runs on the remote target and does not load any debugging information
            from the debugged process.
            Instead, a GDB instance processes the debugging information that is run on a
            remote computer - the host GDB.
            The host GDB then sends control commands to Gdbserver to make it stop or start the debugged
            program, as well as read or write memory regions of that debugged program.
            All the debugging information loaded and processed as well
            as all the heavy debugging is done by the host GDB.
            Offloading these processes gives the Gdbserver running on the target a chance to remain
            small and fast.
        </para>

        <para>
            Because the host GDB is responsible for loading the debugging information and
            for doing the necessary processing to make actual debugging happen, the
            user has to make sure the host can access the unstripped binaries complete
            with their debugging information and also be sure the target is compiled with no optimizations.
            The host GDB must also have local access to all the libraries used by the
            debugged program.
            Because Gdbserver does not need any local debugging information, the binaries on
            the remote target can remain stripped.
            However, the binaries must also be compiled without optimization
            so they match the host's binaries.
        </para>

        <para>
            To remain consistent with GDB documentation and terminology, the binary being debugged
            on the remote target machine is referred to as the "inferior" binary.
            For documentation on GDB see the
            <ulink url="http://sourceware.org/gdb/documentation/">GDB site</ulink>.
        </para>

        <para>
            The remainder of this section describes the steps you need to take
            to debug using the GNU project debugger.
        </para>

        <section id='platdev-gdb-remotedebug-setup'>
            <title>Set Up the Cross-Development Debugging Environment</title>

            <para>
                Before you can initiate a remote debugging session, you need
                to be sure you have set up the cross-development environment,
                toolchain, and sysroot.
                The "<ulink url='&YOCTO_DOCS_ADT_URL;#adt-prepare'>Preparing for Application Development</ulink>"
                chapter of the Yocto Project Application Developer's Guide
                describes this process.
                Be sure you have read that chapter and have set up
                your environment.
            </para>
        </section>

        <section id="platdev-gdb-remotedebug-launch-gdbserver">
            <title>Launch Gdbserver on the Target</title>

            <para>
                Make sure Gdbserver is installed on the target.
                If it is not, install the package
                <filename>gdbserver</filename>, which needs the
                <filename>libthread-db1</filename> package.
            </para>

            <para>
                Here is an example that when entered from the host
                connects to the target and launches Gdbserver in order to
                "debug" a binary named <filename>helloworld</filename>:
                <literallayout class='monospaced'>
     $ gdbserver localhost:2345 /usr/bin/helloworld
                </literallayout>
                Gdbserver should now be listening on port 2345 for debugging
                commands coming from a remote GDB process that is running on
                the host computer.
                Communication between Gdbserver and the host GDB are done
                using TCP.
                To use other communication protocols, please refer to the
                <ulink url='http://www.gnu.org/software/gdb/'>Gdbserver documentation</ulink>.
            </para>
        </section>

        <section id="platdev-gdb-remotedebug-launch-gdb">
            <title>Launch GDB on the Host Computer</title>

            <para>
                Running GDB on the host computer takes a number of stages, which
                this section describes.
            </para>

            <section id="platdev-gdb-remotedebug-launch-gdb-buildcross">
                <title>Build the Cross-GDB Package</title>
                <para>
                    A suitable GDB cross-binary is required that runs on your
                    host computer but also knows about the the ABI of the
                    remote target.
                    You can get this binary from the
                    <link linkend='cross-development-toolchain'>Cross-Development Toolchain</link>.
                    Here is an example where the toolchain has been installed
                    in the default directory
                    <filename>/opt/poky/&DISTRO;</filename>:
                    <literallayout class='monospaced'>
     /opt/poky/&DISTRO;/sysroots/i686-pokysdk-linux/usr/bin/armv7a-vfp-neon-poky-linux-gnueabi/arm-poky-linux-gnueabi-gdb
                    </literallayout>
                    where <filename>arm</filename> is the target architecture
                    and <filename>linux-gnueabi</filename> is the target ABI.
                </para>

                <para>
                    Alternatively, you can use BitBake to build the
                    <filename>gdb-cross</filename> binary.
                    Here is an example:
                    <literallayout class='monospaced'>
     $ bitbake gdb-cross
                    </literallayout>
                    Once the binary is built, you can find it here:
                    <literallayout class='monospaced'>
     tmp/sysroots/&lt;host-arch&gt;/usr/bin/&lt;target-platform&gt;/&lt;target-abi&gt;-gdb
                    </literallayout>
                </para>
            </section>

            <section id='create-the-gdb-initialization-file'>
                <title>Create the GDB Initialization File and Point to Your Root Filesystem</title>

                <para>
                    Aside from the GDB cross-binary, you also need a GDB
                    initialization file in the same top directory in which
                    your binary resides.
                    When you start GDB on your host development system, GDB
                    finds this initialization file and executes all the
                    commands within.
                    For information on the <filename>.gdbinit</filename>, see
                    "<ulink url='http://sourceware.org/gdb/onlinedocs/gdb/'>Debugging with GDB</ulink>",
                    which is maintained by
                    <ulink url='http://www.sourceware.org'>sourceware.org</ulink>.
                </para>

                <para>
                    You need to add a statement in the
                    <filename>.gdbinit</filename> file that points to your
                    root filesystem.
                    Here is an example that points to the root filesystem for
                    an ARM-based target device:
                    <literallayout class='monospaced'>
     set sysroot /home/jzhang/sysroot_arm
                    </literallayout>
                </para>
            </section>

            <section id="platdev-gdb-remotedebug-launch-gdb-launchhost">
                <title>Launch the Host GDB</title>

                <para>
                    Before launching the host GDB, you need to be sure
                    you have sourced the cross-debugging environment script,
                    which if you installed the root filesystem in the default
                    location is at <filename>/opt/poky/&DISTRO;</filename>
                    and begins with the string "environment-setup".
                    For more information, see the
                    "<ulink url='&YOCTO_DOCS_ADT_URL;#setting-up-the-cross-development-environment'>Setting Up the Cross-Development Environment</ulink>"
                    section in the Yocto Project Application Developer's
                    Guide.
                </para>

                <para>
                    Finally, switch to the directory where the binary resides
                    and run the <filename>cross-gdb</filename> binary.
                    Provide the binary file you are going to debug.
                    For example, the following command continues with the
                    example used in the previous section by loading
                    the <filename>helloworld</filename> binary as well as the
                    debugging information:
                    <literallayout class='monospaced'>
     $ arm-poky-linux-gnuabi-gdb helloworld
                    </literallayout>
                    The commands in your <filename>.gdbinit</filename> execute
                    and the GDB prompt appears.
                </para>
            </section>
        </section>

        <section id='platdev-gdb-connect-to-the-remote-gdb-server'>
            <title>Connect to the Remote GDB Server</title>

            <para>
                From the target, you need to connect to the remote GDB
                server that is running on the host.
                You need to specify the remote host and port.
                Here is the command continuing with the example:
                <literallayout class='monospaced'>
     target remote 192.168.7.2:2345
                </literallayout>
            </para>
        </section>

        <section id="platdev-gdb-remotedebug-launch-gdb-using">
            <title>Use the Debugger</title>

            <para>
                You can now proceed with debugging as normal - as if you were debugging
                on the local machine.
                For example, to instruct GDB to break in the "main" function and then
                continue with execution of the inferior binary use the following commands
                from within GDB:
                <literallayout class='monospaced'>
     (gdb) break main
     (gdb) continue
                </literallayout>
            </para>

            <para>
                For more information about using GDB, see the project's online documentation at
                <ulink url="http://sourceware.org/gdb/download/onlinedocs/"/>.
            </para>
        </section>
    </section>

    <section id="examining-builds-using-toaster">
        <title>Examining Builds Using the Toaster API</title>

        <para>
            Toaster is an Application Programming Interface (API) and
            web-based interface to the OpenEmbedded build system, which uses
            BitBake.
            Both interfaces are based on a Representational State Transfer
            (REST) API that queries for and returns build information using
            <filename>GET</filename> and <filename>JSON</filename>.
            These types of search operations retrieve sets of objects from
            a datastore used to collect build information.
            The results contain all the data for the objects being returned.
            You can order the results of the search by key and the search
            parameters are consistent for all object types.
        </para>

        <para>
            Using the interfaces you can do the following:
            <itemizedlist>
                <listitem><para>See information about the tasks executed
                    and reused during the build.</para></listitem>
                <listitem><para>See what is built (recipes and
                    packages) and what packages were installed into the final
                    image.</para></listitem>
                <listitem><para>See performance-related information such
                    as build time, CPU usage, and disk I/O.</para></listitem>
                <listitem><para>Examine error, warning and trace messages
                    to aid in debugging.</para></listitem>
            </itemizedlist>
        </para>

        <note>
            <para>This release of Toaster provides you with information
            about a BitBake run.
            The tool does not allow you to configure and launch a build.
            However, future development includes plans to integrate the
            configuration and build launching capabilities of
            <ulink url='&YOCTO_HOME_URL;/tools-resources/projects/hob'>Hob</ulink>.
            </para>
            <para>For more information on using Hob to build an image,
            see the
            "<link linkend='image-development-using-hob'>Image Development Using Hob</link>"
            section.</para>
        </note>

        <para>
            The remainder of this section describes what you need to have in
            place to use Toaster, how to start it, use it, and stop it.
            For additional information on installing and running Toaster, see the
            "<ulink url='https://wiki.yoctoproject.org/wiki/Toaster#Installation_and_Running'>Installation and Running</ulink>"
            section of the "Toaster" wiki page.
            For complete information on the API and its search operation
            URI, parameters, and responses, see the
            <ulink url='https://wiki.yoctoproject.org/wiki/REST_API_Contracts'>REST API Contracts</ulink>
            Wiki page.
        </para>

        <section id='starting-toaster'>
            <title>Starting Toaster</title>

            <para>
                Getting set up to use and start Toaster is simple.
                First, be sure you have met the following requirements:
                <itemizedlist>
                    <listitem><para>You have set up your
                        <link linkend='source-directory'>Source Directory</link>
                        by cloning the upstream <filename>poky</filename>
                        repository.
                        See the
                        <link linkend='local-yp-release'>Yocto Project Release</link>
                        item for information on how to set up the Source
                        Directory.</para></listitem>
                    <listitem><para>Be sure your build machine has
                        <ulink url='http://en.wikipedia.org/wiki/Django_%28web_framework%29'>Django</ulink>
                        version 1.5 installed.</para></listitem>
                    <listitem><para>Make sure that port 8000 and 8200 are
                        free (i.e. they have no servers on them).
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                Once you have met the requirements, follow these steps to
                start Toaster running in the background of your shell:
                <orderedlist>
                    <listitem><para><emphasis>Set up your build environment:</emphasis>
                        Source a build environment script (i.e.
                        <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>
                        or
                        <ulink url='&YOCTO_DOCS_REF_URL;#structure-memres-core-script'><filename>oe-init-build-env-memres</filename></ulink>).
                        </para></listitem>
                    <listitem><para><emphasis>Start Toaster:</emphasis>
                        Start the Toaster service using this
                        command from within your
                        <link linkend='build-directory'>Build Directory</link>:
                        <literallayout class='monospaced'>
     $ source toaster start
                        </literallayout></para></listitem>
                        <note>
                            The Toaster must be started and running in order
                            for it to collect data.
                        </note>
                </orderedlist>
            </para>

            <para>
                When Toaster starts, it creates some additional files in your
                Build Directory.
                Deleting these files will cause you to lose data or interrupt
                Toaster:
                <itemizedlist>
                    <listitem><para><emphasis><filename>toaster.sqlite</filename>:</emphasis>
                        Toaster's database file.</para></listitem>
                    <listitem><para><emphasis><filename>toaster_web.log</filename>:</emphasis>
                        The log file of the web server.</para></listitem>
                    <listitem><para><emphasis><filename>toaster_ui.log</filename>:</emphasis>
                        The log file of the user interface component.
                        </para></listitem>
                    <listitem><para><emphasis><filename>toastermain.pid</filename>:</emphasis>
                        The PID of the web server.</para></listitem>
                    <listitem><para><emphasis><filename>toasterui.pid</filename>:</emphasis>
                        The PID of the DSI data bridge.</para></listitem>
                    <listitem><para><emphasis><filename>bitbake-cookerdaemon.log</filename>:</emphasis>
                        The BitBake server's log file.</para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='using-toaster'>
            <title>Using Toaster</title>

            <para>
                Once Toaster is running, it logs information for any BitBake
                run from your Build Directory.
                This logging is automatic.
                All you need to do is access and use the information.
            </para>

            <para>
                You access the information one of two ways:
                <itemizedlist>
                    <listitem><para>Open a Browser and enter
                        <filename>http://localhost:8000</filename>
                        for the URL.
                        </para></listitem>
                    <listitem><para>Use the <filename>xdg-open</filename>
                        tool from the shell and pass it the same URL.
                        </para></listitem>
                </itemizedlist>
                Either method opens the home page for the Toaster interface.
            </para>

            <note><title>Notes</title>
                <para>
                    For information on how to delete information from the Toaster
                    database, see the
                    <ulink url='https://wiki.yoctoproject.org/wiki/Toaster#Deleting_a_Build_from_the_Toaster_Database'>Deleting a Build from the Toaster Database</ulink>
                    wiki page.
                </para>

                <para>
                    For information on how to set up an instance of Toaster on
                    a remote host, see the
                    <ulink url='https://wiki.yoctoproject.org/wiki/Toaster#Setting_up_a_Toaster_Instance_on_a_Remote_Host'>Setting Up a Toaster Instance on a Remote Host</ulink>
                    wiki page.
                </para>
            </note>
        </section>

        <section id='examining-toaster-data'>
            <title>Examining Toaster Data</title>

            <para>
                The Toaster database is persistent regardless of whether you
                start or stop the service.
            </para>

            <para>
                Toaster's interface shows you a list of builds
                (successful and unsuccessful) for which it has data.
                You can click on any build to see related information.
                This information includes configuration details, information
                about tasks, all recipes and packages built and their
                dependencies, packages and their directory structure as
                installed in your final image,
                execution time, CPU usage and disk I/O per task.
            </para>

            <para>
                For details on the interface, see the
                <ulink url='https://www.yoctoproject.org/documentation/toaster-manual'>Toaster Manual</ulink>.
            </para>
        </section>

        <section id='stopping-toaster'>
            <title>Stopping Toaster</title>

            <para>
                Stop the Toaster service with the following command
                from with the
                <link linkend='build-directory'>Build Directory</link>:
                <literallayout class='monospaced'>
     $ source toaster stop
                </literallayout>
                The service stops but the Toaster database remains persistent.
            </para>
        </section>
    </section>

    <section id="platdev-oprofile">
        <title>Profiling with OProfile</title>

        <para>
            <ulink url="http://oprofile.sourceforge.net/">OProfile</ulink> is a
            statistical profiler well suited for finding performance
            bottlenecks in both user-space software and in the kernel.
            This profiler provides answers to questions like "Which functions does my application spend
            the most time in when doing X?"
            Because the OpenEmbedded build system is well integrated with OProfile, it makes profiling
            applications on target hardware straight forward.
            <note>
                For more information on how to set up and run OProfile, see the
                "<ulink url='&YOCTO_DOCS_PROF_URL;#profile-manual-oprofile'>oprofile</ulink>"
                section in the Yocto Project Profiling and Tracing Manual.
            </note>
        </para>

        <para>
            To use OProfile, you need an image that has OProfile installed.
            The easiest way to do this is with "tools-profile" in the
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'>IMAGE_FEATURES</ulink></filename> variable.
            You also need debugging symbols to be available on the system where the analysis
            takes place.
            You can gain access to the symbols by using "dbg-pkgs" in the
            <filename>IMAGE_FEATURES</filename> variable or by
            installing the appropriate DBG (<filename>-dbg</filename>) packages.
        </para>

        <para>
            For successful call graph analysis, the binaries must preserve the frame
            pointer register and should also be compiled with the
            <filename>-fno-omit-framepointer</filename> flag.
            You can achieve this by setting the
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SELECTED_OPTIMIZATION'>SELECTED_OPTIMIZATION</ulink></filename>
            variable with the following options:
            <literallayout class='monospaced'>
     -fexpensive-optimizations
     -fno-omit-framepointer
     -frename-registers
     -O2
            </literallayout>
            You can also achieve it by setting the
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-DEBUG_BUILD'>DEBUG_BUILD</ulink></filename>
            variable to "1" in the <filename>local.conf</filename> configuration file.
            If you use the <filename>DEBUG_BUILD</filename> variable,
            you also add extra debugging information that can make the debug
            packages large.
        </para>

        <section id="platdev-oprofile-target">
            <title>Profiling on the Target</title>

            <para>
                Using OProfile, you can perform all the profiling work on the target device.
                A simple OProfile session might look like the following:
            </para>

            <para>
                <literallayout class='monospaced'>
     # opcontrol --reset
     # opcontrol --start --separate=lib --no-vmlinux -c 5
              .
              .
        [do whatever is being profiled]
              .
              .
     # opcontrol --stop
     $ opreport -cl
                </literallayout>
            </para>

            <para>
                In this example, the <filename>reset</filename> command clears any previously profiled data.
                The next command starts OProfile.
                The options used when starting the profiler separate dynamic library data
                within applications, disable kernel profiling, and enable callgraphing up to
                five levels deep.
                <note>
                    To profile the kernel, you would specify the
                    <filename>--vmlinux=/path/to/vmlinux</filename> option.
                    The <filename>vmlinux</filename> file is usually in the source directory in the
                    <filename>/boot/</filename> directory and must match the running kernel.
                </note>
            </para>

            <para>
                After you perform your profiling tasks, the next command stops the profiler.
                After that, you can view results with the <filename>opreport</filename> command with options
                to see the separate library symbols and callgraph information.
            </para>

            <para>
                Callgraphing logs information about time spent in functions and about a function's
                calling function (parent) and called functions (children).
                The higher the callgraphing depth, the more accurate the results.
                However, higher depths also increase the logging overhead.
                Consequently, you should take care when setting the callgraphing depth.
                <note>
                    On ARM, binaries need to have the frame pointer enabled for callgraphing to work.
                    To accomplish this use the <filename>-fno-omit-framepointer</filename> option
                    with <filename>gcc</filename>.
                </note>
            </para>

            <para>
                For more information on using OProfile, see the OProfile
                online documentation at
                <ulink url="http://oprofile.sourceforge.net/docs/"/>.
            </para>
        </section>

        <section id="platdev-oprofile-oprofileui">
            <title>Using OProfileUI</title>

            <para>
                A graphical user interface for OProfile is also available.
                You can download and build this interface from the Yocto Project at
                <ulink url="&YOCTO_GIT_URL;/cgit.cgi/oprofileui/"></ulink>.
                If the "tools-profile" image feature is selected, all necessary binaries
                are installed onto the target device for OProfileUI interaction.
                For a list of image features that ship with the Yocto Project,
                see the
                "<ulink url='&YOCTO_DOCS_REF_URL;#ref-features-image'>Image Features</ulink>"
                section in the Yocto Project Reference Manual.
            </para>

            <para>
                Even though the source directory usually includes all needed patches on the target device, you
                might find you need other OProfile patches for recent OProfileUI features.
                If so, see the <ulink url='&YOCTO_GIT_URL;/cgit.cgi/oprofileui/tree/README'>
                OProfileUI README</ulink> for the most recent information.
            </para>

            <section id="platdev-oprofile-oprofileui-online">
                <title>Online Mode</title>

                <para>
                    Using OProfile in online mode assumes a working network connection with the target
                    hardware.
                    With this connection, you just need to run "oprofile-server" on the device.
                    By default, OProfile listens on port 4224.
                    <note>
                        You can change the port using the <filename>--port</filename> command-line
                        option.
                    </note>
                </para>

                <para>
                    The client program is called <filename>oprofile-viewer</filename> and its UI is relatively
                    straight forward.
                    You access key functionality through the buttons on the toolbar, which
                    are duplicated in the menus.
                    Here are the buttons:
                    <itemizedlist>
                        <listitem><para><emphasis>Connect:</emphasis> Connects to the remote host.
                            You can also supply the IP address or hostname.</para></listitem>
                        <listitem><para><emphasis>Disconnect:</emphasis> Disconnects from the target.
                            </para></listitem>
                        <listitem><para><emphasis>Start:</emphasis> Starts profiling on the device.
                            </para></listitem>
                        <listitem><para><emphasis>Stop:</emphasis> Stops profiling on the device and
                            downloads the data to the local host.
                            Stopping the profiler generates the profile and displays it in the viewer.
                            </para></listitem>
                        <listitem><para><emphasis>Download:</emphasis> Downloads the data from the
                            target and generates the profile, which appears in the viewer.</para></listitem>
                        <listitem><para><emphasis>Reset:</emphasis> Resets the sample data on the device.
                            Resetting the data removes sample information collected from previous
                            sampling runs.
                            Be sure you reset the data if you do not want to include old sample information.
                            </para></listitem>
                        <listitem><para><emphasis>Save:</emphasis> Saves the data downloaded from the
                            target to another directory for later examination.</para></listitem>
                        <listitem><para><emphasis>Open:</emphasis> Loads previously saved data.
                            </para></listitem>
                    </itemizedlist>
                </para>

                <para>
                    The client downloads the complete profile archive from
                    the target to the host for processing.
                    This archive is a directory that contains the sample data, the object files,
                    and the debug information for the object files.
                    The archive is then converted using the <filename>oparchconv</filename> script, which is
                    included in this distribution.
                    The script uses <filename>opimport</filename> to convert the archive from
                    the target to something that can be processed on the host.
                </para>

                <para>
                    Downloaded archives reside in the
                    <link linkend='build-directory'>Build Directory</link> in
                    <filename>tmp</filename> and are cleared up when they are no longer in use.
                </para>

                <para>
                    If you wish to perform kernel profiling, you need to be sure
                    a <filename>vmlinux</filename> file that matches the running kernel is available.
                    In the source directory, that file is usually located in
                    <filename>/boot/vmlinux-KERNELVERSION</filename>, where
                    <filename>KERNEL-version</filename> is the version of the kernel.
                    The OpenEmbedded build system generates separate <filename>vmlinux</filename>
                    packages for each kernel it builds.
                    Thus, it should just be a question of making sure a matching package is
                    installed (e.g. <filename>opkg install kernel-vmlinux</filename>).
                    The files are automatically installed into development and profiling images
                    alongside OProfile.
                    A configuration option exists within the OProfileUI settings page that you can use to
                    enter the location of the <filename>vmlinux</filename> file.
                </para>

                <para>
                    Waiting for debug symbols to transfer from the device can be slow, and it
                    is not always necessary to actually have them on the device for OProfile use.
                    All that is needed is a copy of the filesystem with the debug symbols present
                    on the viewer system.
                    The "<link linkend='platdev-gdb-remotedebug-launch-gdb'>Launch GDB on the Host Computer</link>"
                    section covers how to create such a directory within
                    the source directory and how to use the OProfileUI Settings
                    Dialog to specify the location.
                    If you specify the directory, it will be used when the file checksums
                    match those on the system you are profiling.
                </para>
            </section>

            <section id="platdev-oprofile-oprofileui-offline">
                <title>Offline Mode</title>

                <para>
                    If network access to the target is unavailable, you can generate
                    an archive for processing in <filename>oprofile-viewer</filename> as follows:
                    <literallayout class='monospaced'>
     # opcontrol --reset
     # opcontrol --start --separate=lib --no-vmlinux -c 5
            .
            .
     [do whatever is being profiled]
            .
            .
     # opcontrol --stop
     # oparchive -o my_archive
                    </literallayout>
                </para>

                <para>
                    In the above example, <filename>my_archive</filename> is the name of the
                    archive directory where you would like the profile archive to be kept.
                    After the directory is created, you can copy it to another host and load it
                    using <filename>oprofile-viewer</filename> open functionality.
                    If necessary, the archive is converted.
                </para>
            </section>
        </section>
    </section>

    <section id='maintaining-open-source-license-compliance-during-your-products-lifecycle'>
        <title>Maintaining Open Source License Compliance During Your Product's Lifecycle</title>

        <para>
            One of the concerns for a development organization using open source
            software is how to maintain compliance with various open source
            licensing during the lifecycle of the product.
            While this section does not provide legal advice or
            comprehensively cover all scenarios, it does
            present methods that you can use to
            assist you in meeting the compliance requirements during a software
            release.
        </para>

        <para>
            With hundreds of different open source licenses that the Yocto
            Project tracks, it is difficult to know the requirements of each
            and every license.
            However, the requirements of the major FLOSS licenses can begin
            to be covered by
            assuming that three main areas of concern exist:
            <itemizedlist>
                <listitem><para>Source code must be provided.</para></listitem>
                <listitem><para>License text for the software must be
                    provided.</para></listitem>
                <listitem><para>Compilation scripts and modifications to the
                    source code must be provided.
                    </para></listitem>
            </itemizedlist>
            There are other requirements beyond the scope of these
            three and the methods described in this section
            (e.g. the mechanism through which source code is distributed).
        </para>

        <para>
            As different organizations have different methods of complying with
            open source licensing, this section is not meant to imply that
            there is only one single way to meet your compliance obligations,
            but rather to describe one method of achieving compliance.
            The remainder of this section describes methods supported to meet the
            previously mentioned three requirements.
            Once you take steps to meet these requirements,
            and prior to releasing images, sources, and the build system,
            you should audit all artifacts to ensure completeness.
            <note>
                The Yocto Project generates a license manifest during
                image creation that is located
                in <filename>${DEPLOY_DIR}/licenses/&lt;image_name-datestamp&gt;</filename>
                to assist with any audits.
            </note>
        </para>

        <section id='providing-the-source-code'>
            <title>Providing the Source Code</title>

            <para>
                Compliance activities should begin before you generate the
                final image.
                The first thing you should look at is the requirement that
                tops the list for most compliance groups - providing
                the source.
                The Yocto Project has a few ways of meeting this
                requirement.
            </para>

            <para>
                One of the easiest ways to meet this requirement is
                to provide the entire
                <ulink url='&YOCTO_DOCS_REF_URL;#var-DL_DIR'><filename>DL_DIR</filename></ulink>
                used by the build.
                This method, however, has a few issues.
                The most obvious is the size of the directory since it includes
                all sources used in the build and not just the source used in
                the released image.
                It will include toolchain source, and other artifacts, which
                you would not generally release.
                However, the more serious issue for most companies is accidental
                release of proprietary software.
                The Yocto Project provides an
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-archiver'><filename>archiver</filename></ulink>
                class to help avoid some of these concerns.
            </para>

            <para>
                Before you employ <filename>DL_DIR</filename> or the
                archiver class, you need to decide how you choose to
                provide source.
                The source archiver class can generate tarballs and SRPMs
                and can create them with various levels of compliance in mind.
            </para>

            <para>
                One way of doing this (but certainly not the only way) is to
                release just the source as a tarball.
                You can do this by adding the following to the
                <filename>local.conf</filename> file found in the
                <link linkend='build-directory'>Build Directory</link>:
                <literallayout class='monospaced'>
     INHERIT += "archiver"
     ARCHIVER_MODE[src] = "original"
                </literallayout>
                During the creation of your image, the source from all
                recipes that deploy packages to the image is placed within
                subdirectories of
                <filename>DEPLOY_DIR/sources</filename> based on the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE'><filename>LICENSE</filename></ulink>
                for each recipe.
                Releasing the entire directory enables you to comply with
                requirements concerning providing the unmodified source.
                It is important to note that the size of the directory can
                get large.
            </para>

            <para>
                A way to help mitigate the size issue is to only release
                tarballs for licenses that require the release of
                source.
                Let us assume you are only concerned with GPL code as
                identified with the following:
                <literallayout class='monospaced'>
     $ cd poky/build/tmp/deploy/sources
     $ mkdir ~/gpl_source_release
     $ for dir in */*GPL*; do cp -r $dir ~/gpl_source_release; done
                </literallayout>
                At this point, you could create a tarball from the
                <filename>gpl_source_release</filename> directory and
                provide that to the end user.
                This method would be a step toward achieving compliance
                with section 3a of GPLv2 and with section 6 of GPLv3.
            </para>
        </section>

        <section id='providing-license-text'>
            <title>Providing License Text</title>

            <para>
                One requirement that is often overlooked is inclusion
                of license text.
                This requirement also needs to be dealt with prior to
                generating the final image.
                Some licenses require the license text to accompany
                the binary.
                You can achieve this by adding the following to your
                <filename>local.conf</filename> file:
                <literallayout class='monospaced'>
     COPY_LIC_MANIFEST = "1"
     COPY_LIC_DIRS = "1"
                </literallayout>
                Adding these statements to the configuration file ensures
                that the licenses collected during package generation
                are included on your image.
                As the source archiver has already archived the original
                unmodified source that contains the license files,
                you would have already met the requirements for inclusion
                of the license information with source as defined by the GPL
                and other open source licenses.
            </para>
        </section>

        <section id='providing-compilation-scripts-and-source-code-modifications'>
            <title>Providing Compilation Scripts and Source Code Modifications</title>

            <para>
                At this point, we have addressed all we need to address
                prior to generating the image.
                The next two requirements are addressed during the final
                packaging of the release.
            </para>

            <para>
                By releasing the version of the OpenEmbedded build system
                and the layers used during the build, you will be providing both
                compilation scripts and the source code modifications in one
                step.
            </para>

            <para>
                If the deployment team has a
                <ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP layer</ulink>
                and a distro layer, and those those layers are used to patch,
                compile, package, or modify (in any way) any open source
                software included in your released images, you
                might be required to to release those layers under section 3 of
                GPLv2 or section 1 of GPLv3.
                One way of doing that is with a clean
                checkout of the version of the Yocto Project and layers used
                during your build.
                Here is an example:
                <literallayout class='monospaced'>
     # We built using the &DISTRO_NAME; branch of the poky repo
     $ git clone -b &DISTRO_NAME; git://git.yoctoproject.org/poky
     $ cd poky
     # We built using the release_branch for our layers
     $ git clone -b release_branch git://git.mycompany.com/meta-my-bsp-layer
     $ git clone -b release_branch git://git.mycompany.com/meta-my-software-layer
     # clean up the .git repos
     $ find . -name ".git" -type d -exec rm -rf {} \;
                </literallayout>
                One thing a development organization might want to consider
                for end-user convenience is to modify
                <filename>meta-yocto/conf/bblayers.conf.sample</filename> to
                ensure that when the end user utilizes the released build
                system to build an image, the development organization's
                layers are included in the <filename>bblayers.conf</filename>
                file automatically:
                <literallayout class='monospaced'>
     # LAYER_CONF_VERSION is increased each time build/conf/bblayers.conf
     # changes incompatibly
     LCONF_VERSION = "6"

     BBPATH = "${TOPDIR}"
     BBFILES ?= ""

     BBLAYERS ?= " \
       ##OEROOT##/meta \
       ##OEROOT##/meta-yocto \
       ##OEROOT##/meta-yocto-bsp \
       ##OEROOT##/meta-mylayer \
       "

     BBLAYERS_NON_REMOVABLE ?= " \
       ##OEROOT##/meta \
       ##OEROOT##/meta-yocto \
       "
                </literallayout>
                Creating and providing an archive of the
                <link linkend='metadata'>Metadata</link> layers
                (recipes, configuration files, and so forth)
                enables you to meet your
                requirements to include the scripts to control compilation
                as well as any modifications to the original source.
            </para>
        </section>
    </section>

    <section id='using-the-error-reporting-tool'>
        <title>Using the Error Reporting Tool</title>

        <para>
            The error reporting tool allows you to
            submit errors encountered during builds to a central database.
            Outside of the build environment, you can use a web interface to
            browse errors, view statistics, and query for errors.
            The tool works using a client-server system where the client
            portion is integrated with the installed Yocto Project
            <link linkend='source-directory'>Source Directory</link>
            (e.g. <filename>poky</filename>).
            The server receives the information collected and saves it in a
            database.
        </para>

        <para>
            A live instance of the error reporting server exists at
            <ulink url='http://errors.yoctoproject.org'></ulink>.
            This server exists so that when you want to get help with
            build failures, you can submit all of the information on the
            failure easily and then point to the URL in your bug report
            or send an email to the mailing list.
            <note>
                If you send error reports to this server, the reports become
                publicly visible.
            </note>
        </para>

        <section id='enabling-and-using-the-tool'>
            <title>Enabling and Using the Tool</title>

            <para>
                By default, the error reporting tool is disabled.
                You can enable it by inheriting the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-report-error'><filename>report-error</filename></ulink>
                class by adding the following statement to the end of
                your <filename>local.conf</filename> file in your
                <link linkend='build-directory'>Build Directory</link>.
                <literallayout class='monospaced'>
     INHERIT += "report-error"
                </literallayout>
            </para>

            <para>
                By default, the error reporting feature stores information in
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LOG_DIR'><filename>LOG_DIR</filename></ulink><filename>}/error-report</filename>.
                However, you can specify a directory to use by adding the following
                to your <filename>local.conf</filename> file:
                <literallayout class='monospaced'>
     ERR_REPORT_DIR = "path"
                </literallayout>
                Enabling error reporting causes the build process to collect
                the errors and store them in a file as previously described.
                When the build system encounters an error, it includes a command
                as part of the console output.
                You can run the command to send the error file to the server.
                For example, the following command sends the errors to an upstream
                server:
                <literallayout class='monospaced'>
     send-error-report /home/brandusa/project/poky/build/tmp/log/error-report/error_report_201403141617.txt [server]
                </literallayout>
                In the above example, the <filename>server</filename> parameter is
                optional.
                By default, the errors are sent to a database used by the entire
                community.
                If you specify a particular server, you can send them to a different
                database.
            </para>

            <para>
                When sending the error file, you receive a link that corresponds
                to your entry in the database.
                For example, here is a typical link:
                <literallayout class='monospaced'>
     http://localhost:8000/Errors/Search/1/158
                </literallayout>
                Following the link takes you to a web interface where you can
                browse, query the errors, and view statistics.
             </para>
        </section>

        <section id='disabling-the-tool'>
            <title>Disabling the Tool</title>

            <para>
                To disable the error reporting feature, simply remove or comment
                out the following statement from the end of your
                <filename>local.conf</filename> file in your
                <link linkend='build-directory'>Build Directory</link>.
                <literallayout class='monospaced'>
     INHERIT += "report-error"
                </literallayout>
            </para>
        </section>

        <section id='setting-up-your-own-error-reporting-server'>
            <title>Setting Up Your Own Error Reporting Server</title>

            <para>
                If you want to set up your own error reporting server, you
                can obtain the code from the Git repository at
                <ulink url='http://git.yoctoproject.org/cgit/cgit.cgi/error-report-web/'></ulink>.
                Instructions on how to set it up are in the README document.
            </para>
        </section>
     </section>
</chapter>

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