path: root/documentation/ref-manual/ref-classes.xml

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

<chapter id='ref-classes'>
<title>Classes</title>

<para>
    Class files are used to abstract common functionality and share it amongst
    multiple recipe (<filename>.bb</filename>) files.
    To use a class file, you simply make sure the recipe inherits the class.
    In most cases, when a recipe inherits a class it is enough to enable its
    features.
    There are cases, however, where in the recipe you might need to set
    variables or override some default behavior.
</para>

<para>
    Any <ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink> usually
    found in a recipe can also be placed in a class file.
    Class files are identified by the extension <filename>.bbclass</filename>
    and are usually placed in a <filename>classes/</filename> directory beneath
    the <filename>meta*/</filename> directory found in the
    <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>.
    Class files can also be pointed to by
    <link linkend='var-BUILDDIR'><filename>BUILDDIR</filename></link>
    (e.g. <filename>build/</filename>) in the same way as
    <filename>.conf</filename> files in the <filename>conf</filename> directory.
    Class files are searched for in
    <link linkend='var-BBPATH'><filename>BBPATH</filename></link>
    using the same method by which <filename>.conf</filename> files are
    searched.
</para>

<para>
    This chapter discusses only the most useful and important classes.
    Other classes do exist within the <filename>meta/classes</filename>
    directory in the
    <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>.
    You can reference the <filename>.bbclass</filename> files directly
    for more information.
</para>

<section id='ref-classes-allarch'>
    <title><filename>allarch.bbclass</filename></title>

    <para>
        The all architecture (<filename>allarch</filename>) class is inherited
        by recipes that do not produce architecture-specific output.
        The class disables functionality that is normally needed for recipes
        that produce executable binaries (such as building the cross-compiler
        and a C library as pre-requisites, and splitting out of debug symbols
        during packaging).
    </para>

    <para>
        By default, all recipes inherit the
        <link linkend='ref-classes-base'><filename>base</filename></link> and
        <link linkend='ref-classes-package'><filename>package</filename></link>
        classes, which enable functionality
        needed for recipes that produce executable output.
        If your recipe, for example, only produces packages that contain
        configuration files, media files, or scripts (e.g. Python and Perl),
        then it should inherit the <filename>allarch</filename> class.
    </para>
</section>

<section id='ref-classes-archiver'>
    <title><filename>archive*.bbclass</filename></title>

    <para>
        The <filename>archive*</filename> set of classes support releasing
        source code and other materials with the binaries.
        This set of classes consists of the following:
        <itemizedlist>
            <listitem><filename>archive-original-sources.bbclass</filename></listitem>
            <listitem><filename>archive-patched-sources.bbclass</filename></listitem>
            <listitem><filename>archive-configured-sources.bbclass</filename></listitem>
            <listitem><filename>archiver.bbclass</filename></listitem>
        </itemizedlist>
    </para>

    <para>
        For more details on the source archiver, see the
        "<ulink url='&YOCTO_DOCS_DEV_URL;#maintaining-open-source-license-compliance-during-your-products-lifecycle'>Maintaining Open Source License Compliance During Your Product's Lifecycle</ulink>"
        section in the Yocto Project Development Manual.
    </para>
</section>

<section id='ref-classes-autotools'>
    <title><filename>autotools.bbclass</filename></title>

    <para>
        The <filename>autotools</filename> class supports Autotooled
        packages.
    </para>

    <para>
        The <filename>autoconf</filename>, <filename>automake</filename>,
        and <filename>libtool</filename> bring standardization.
        This class defines a set of tasks (configure, compile etc.) that
        work for all Autotooled packages.
        It should usually be enough to define a few standard variables
        and then simply <filename>inherit autotools</filename>.
        This class can also work with software that emulates Autotools.
        For more information, see the
        "<ulink url='&YOCTO_DOCS_DEV_URL;#usingpoky-extend-addpkg-autotools'>Autotooled Package</ulink>"
        section in the Yocto Project Development Manual.
    </para>

    <para>
        It's useful to have some idea of how the tasks defined by this class work
        and what they do behind the scenes.
        <itemizedlist>
            <listitem><para><filename>do_configure</filename> &dash; Regenerates the
                configure script (using <filename>autoreconf</filename>) and then launches it
                with a standard set of arguments used during cross-compilation.
                You can pass additional parameters to <filename>configure</filename> through the
                <filename><link linkend='var-EXTRA_OECONF'>EXTRA_OECONF</link></filename> variable.
                </para></listitem>
            <listitem><para><filename>do_compile</filename> &dash; Runs <filename>make</filename> with
                arguments that specify the compiler and linker.
                You can pass additional arguments through
                the <filename><link linkend='var-EXTRA_OEMAKE'>EXTRA_OEMAKE</link></filename> variable.
                </para></listitem>
            <listitem><para><filename>do_install</filename> &dash; Runs <filename>make install</filename>
                and passes in
                <filename>${</filename><link linkend='var-D'><filename>D</filename></link><filename>}</filename>
                as <filename>DESTDIR</filename>.
                </para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='ref-classes-base'>
    <title><filename>base.bbclass</filename></title>

    <para>
        The <filename>base</filename> class is special in that every
        <filename>.bb</filename> file automatically inherits the class.
        This class contains definitions for standard basic
        tasks such as fetching, unpacking, configuring (empty by default),
        compiling (runs any <filename>Makefile</filename> present), installing
        (empty by default) and packaging (empty by default).
        These classes are often overridden or extended by other classes
        such as the
        <link linkend='ref-classes-autotools'><filename>autotools</filename></link>
        class or the
        <link linkend='ref-classes-package'><filename>package</filename></link>
        class.
        The class also contains some commonly used functions such as
        <filename>oe_runmake</filename>.
    </para>
</section>

<section id='ref-classes-bin-package'>
    <title><filename>bin_package.bbclass</filename></title>

    <para>
        The <filename>bin_package</filename> class is a
        helper class for recipes that extract the contents of a binary package
        (e.g. an RPM) and install those contents rather than building the
        binary from source.
        The binary package is extracted and new packages in the configured
        output package format are created.
        <note>
            For RPMs and other packages that do not contain a subdirectory,
            you should specify a "subdir" parameter.
            Here is an example where <filename>${BP}</filename> matches the
            subdirectory expected by the default value of
            <link linkend='var-S'><filename>S</filename></link>:
            <literallayout class='monospaced'>
     SRC_URI = "http://example.com/downloads/somepackage.rpm;subdir=${BP}"
            </literallayout>
        </note>
    </para>
</section>

<section id='ref-classes-binconfig'>
    <title><filename>binconfig.bbclass</filename></title>

    <para>
        The <filename>binconfig</filename> class helps to correct paths in
        shell scripts.
    </para>

    <para>
        Before <filename>pkg-config</filename> had become widespread, libraries
        shipped shell scripts to give information about the libraries and
        include paths needed to build software (usually named
        <filename>LIBNAME-config</filename>).
        This class assists any recipe using such scripts.
    </para>

    <para>
        During staging, the OpenEmbedded build system installs such scripts
        into the <filename>sysroots/</filename> directory.
        Inheriting this class results in all paths in these scripts being
        changed to point into the <filename>sysroots/</filename> directory so
        that all builds that use the script use the correct directories
        for the cross compiling layout.
        See the
        <link linkend='var-BINCONFIG_GLOB'><filename>BINCONFIG_GLOB</filename></link>
        variable for more information.
    </para>
</section>

<section id='ref-classes-blacklist'>
    <title><filename>blacklist.bbclass</filename></title>

    <para>
        The <filename>blacklist</filename> class prevents
        the OpenEmbedded build system from building specific recipes
        (blacklists them).
        To use this class, inherit the class globally and set
        <link linkend='var-PNBLACKLIST'><filename>PNBLACKLIST</filename></link>
        for each recipe you wish to blacklist.
        Specify the <link linkend='var-PN'><filename>PN</filename></link>
        value as a variable flag (varflag) and provide a reason, which is
        reported, if the package is requested to be built as the value.
        For example, if you want to blacklist a recipe called "exoticware",
        you add the following to your <filename>local.conf</filename>
        or distribution configuration:
        <literallayout class='monospaced'>
     INHERIT += "blacklist"
     PNBLACKLIST[exoticware] = "Not supported by our organization."
        </literallayout>
    </para>
</section>

<section id='ref-classes-boot-directdisk'>
    <title><filename>boot-directdisk.bbclass</filename></title>

    <para>
        The <filename>boot-directdisk</filename> class
        creates an image that can be placed directly onto a hard disk using
        <filename>dd</filename> and then booted.
        The image uses SYSLINUX.
    </para>

    <para>
        The end result is a 512 boot sector populated with a
        Master Boot Record (MBR) and partition table followed by an MSDOS
        FAT16 partition containing SYSLINUX and a Linux kernel completed by
        the <filename>ext2</filename> and <filename>ext3</filename>
        root filesystems.
    </para>
</section>

<section id='ref-classes-bootimg'>
    <title><filename>bootimg.bbclass</filename></title>

    <para>
        The <filename>bootimg</filename> class creates a bootable
        image using SYSLINUX, your kernel and an optional initial RAM disk
        (<filename>initrd</filename>).
    </para>

    <para>
        When you use this class, two things happen:
        <itemizedlist>
            <listitem><para>
                A <filename>.hddimg</filename> file is created.
                This file which is an MSDOS filesystem that contains SYSLINUX,
                a kernel, an <filename>initrd</filename>, and a root filesystem
                image.
                All three of these can be written to hard drives directly and
                also booted on a USB flash disks using <filename>dd</filename>.
                </para></listitem>
            <listitem><para>
                A CD <filename>.iso</filename> image is created.
                When this file is booted, the <filename>initrd</filename>
                boots and processes the label selected in SYSLINUX.
                Actions based on the label are then performed (e.g. installing
                to a hard drive).</para></listitem>
        </itemizedlist>
    </para>

    <para>
        The <filename>bootimg</filename> class supports the
        <link linkend='var-INITRD'><filename>INITRD</filename></link>,
        <link linkend='var-NOISO'><filename>NOISO</filename></link>,
        <link linkend='var-NOHDD'><filename>NOHDD</filename></link>, and
        <link linkend='var-ROOTFS'><filename>ROOTFS</filename></link>
        variables.
    </para>
</section>

<section id='ref-classes-bugzilla'>
    <title><filename>bugzilla.bbclass</filename></title>

    <para>
        The <filename>bugzilla</filename> class, if enabled in
        your instance of Bugzilla, automatically files bug reports to that
        enabled instance in response to build failures.
        This class uses Bugzilla's XML-RPC interface.
    </para>
</section>

<section id='ref-classes-buildhistory'>
    <title><filename>buildhistory.bbclass</filename></title>

    <para>
        The <filename>buildhistory</filename> class records a
        history of build output metadata, which can be used to detect possible
        regressions as well as used for analysis of the build output.
        For more information on using Build History, see the
        "<link linkend='maintaining-build-output-quality'>Maintaining Build Output Quality</link>"
        section.
    </para>
</section>

<section id='ref-classes-buildstats'>
    <title><filename>buildstats.bbclass</filename></title>

    <para>
        The <filename>buildstats</filename> class records
        performance statistics about each task executed during the build
        (e.g. elapsed time, CPU usage, and I/O usage).
    </para>

    <para>
        When you use this class, the output goes into the
        <link linkend='var-BUILDSTATS_BASE'><filename>BUILDSTATS_BASE</filename></link>
        directory, which defaults to <filename>${TMPDIR}/buildstats/</filename>.
        You can analyze the elapsed time using
        <filename>scripts/pybootchartgui/pybootchartgui.py</filename>, which
        produces a cascading chart of the entire build process and can be
        useful for highlighting bottlenecks.
    </para>

    <para>
        To enable this class, use the
        <link linkend='var-USER_CLASSES'><filename>USER_CLASSES</filename></link>
        variable from your <filename>local.conf</filename> file.
        The <filename>meta-yocto/conf/local.conf.sample</filename> file
        in the
        <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>
        enables this class by default.
    </para>
</section>

<section id='ref-classes-ccache'>
    <title><filename>ccache.bbclass</filename></title>

    <para>
        The <filename>ccache</filename> class enables this cache for the build.
        This class is used to give a minor performance boost during the build.
        However, using the class can lead to unexpected side-effects.
        Thus, it is recommended that you do not use this class.
        See <ulink url='http://ccache.samba.org/'></ulink> for information on
        the C/C++ Compiler Cache.
    </para>
</section>

<section id='ref-classes-chrpath'>
    <title><filename>chrpath.bbclass</filename></title>

    <para>
        The <filename>chrpath</filename> class
        is a wrapper around the "chrpath" utility, which is used during the
        build process for <filename>nativesdk</filename> recipes to change
        <filename>RPATH</filename> records within binaries in order to make
        them relocatable.
    </para>
</section>

<section id='ref-classes-clutter'>
    <title><filename>clutter.bbclass</filename></title>

    <para>
        The <filename>clutter</filename> class consolidates the
        major and minor version naming and other common items used by Clutter
        and related recipes.
    </para>
</section>

<section id='ref-classes-cmake'>
    <title><filename>cmake.bbclass</filename></title>

    <para>
        The <filename>cmake</filename> class allows for
        recipes that need to build software using the CMake build system.
        You can use the
        <link linkend='var-EXTRA_OECMAKE'><filename>EXTRA_OECMAKE</filename></link>
        variable to specify additional configuration options to be passed on
        the <filename>cmake</filename> command line.
    </para>
</section>

<section id='ref-classes-cml1'>
    <title><filename>cml1.bbclass</filename></title>

    <para>
        The <filename>cml1</filename> class provides basic support for the
        Linux kernel style build configuration system.
    </para>
</section>

<section id='ref-classes-copyleft_compliance'>
    <title><filename>copyleft_compliance.bbclass</filename></title>

    <para>
        The <filename>copyleft_compliance</filename> class
        preserves source code for the purposes of license compliance.
        This class is an alternative to the <filename>archive*</filename>
        classes and is still used by some users even though it has been
        deprecated in favor of the
        <link linkend='ref-classes-archiver'><filename>archive*</filename></link>
        classes.
    </para>
</section>

<section id='ref-classes-core-image'>
    <title><filename>core-image.bbclass</filename></title>

    <para>
        The <filename>core-image</filename> class
        provides common definitions for the
        <filename>core-image-*</filename> image recipes, such as support for
        additional
        <link linkend='var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></link>.
    </para>
</section>

<section id='ref-classes-cpan'>
    <title><filename>cpan.bbclass</filename></title>

    <para>
        The <filename>cpan</filename> class supports Perl modules.
    </para>

    <para>
        Recipes for Perl modules are simple.
        These recipes usually only need to point to the source's archive and
        then inherit the proper class file.
        Building is split into two methods depending on which method the module
        authors used.
        <itemizedlist>
            <listitem><para>Modules that use old
                <filename>Makefile.PL</filename>-based build system require
                <filename>cpan.bbclass</filename> in their recipes.
                </para></listitem>
            <listitem><para>Modules that use
                <filename>Build.PL</filename>-based build system require
                using <filename>cpan_build.bbclass</filename> in their recipes.
                </para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='ref-classes-cross'>
    <title><filename>cross.bbclass</filename></title>

    <para>
        The <filename>cross</filename>)class provides support for
        cross-compilation tools.
    </para>
</section>

<section id='ref-classes-cross-canadian'>
    <title><filename>cross-canadian.bbclass</filename></title>

    <para>
        The <filename>cross-canadian</filename> class
        provides support for Canadian Cross compilation tools for SDKs.
        See the
        "<link linkend='cross-development-toolchain-generation'>Cross-Development Toolchain Generation</link>"
        section for more discussion on these cross-compilation tools.
    </para>
</section>

<section id='ref-classes-crosssdk'>
    <title><filename>crosssdk.bbclass</filename></title>

    <para>
        The <filename>crosssdk</filename> class
        provides support for cross-compilation tools used for building
        SDKs.
        See the
        "<link linkend='cross-development-toolchain-generation'>Cross-Development Toolchain Generation</link>"
        section for more discussion on these cross-compilation tools.
    </para>
</section>

<section id='ref-classes-debian'>
    <title><filename>debian.bbclass</filename></title>

    <para>
        The <filename>debian</filename> class renames packages so that they
        follow the Debian naming policy (i.e. <filename>eglibc</filename>
        becomes <filename>libc6</filename> and <filename>eglibc-devel</filename>
        becomes <filename>libc6-dev</filename>.)
    </para>
</section>

<section id='ref-classes-deploy'>
    <title><filename>deploy.bbclass</filename></title>

    <para>
        The <filename>deploy</filename> class handles deploying files
        to the
        <link linkend='var-DEPLOY_DIR_IMAGE'><filename>DEPLOY_DIR_IMAGE</filename></link>
        directory.
        The main function of this class is to allow the deploy step to be
        accelerated by shared state.
        Recipes that inherit this class should define their own
        <filename>do_deploy</filename> function to copy the files to be
        deployed to
        <link linkend='var-DEPLOY_DIR'><filename>DEPLOYDIR</filename></link>,
        and use <filename>addtask</filename> to add the task at the appropriate
        place, which is usually after <filename>do_compile</filename> or
        <filename>do_install</filename>.
    </para>
</section>

<section id='ref-classes-devshell'>
    <title><filename>devshell.bbclass</filename></title>

    <para>
        The <filename>devshell</filename> class adds the
        <filename>devshell</filename> task.
        Distribution policy dictates whether to include this class.
        See the
        "<ulink url='&YOCTO_DOCS_DEV_URL;#platdev-appdev-devshell'>Using a Development Shell</ulink>" section
        in the Yocto Project Development Manual for more information about
        using <filename>devshell</filename>.
    </para>
</section>

<section id='ref-classes-distro_features_check'>
    <title><filename>distro_features_check.bbclass</filename></title>

    <para>
        The <filename>distro_features_check</filename> class
        allows individual recipes to check for required and conflicting
        <link linkend='var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></link>.
    </para>

    <para>
        This class provides support for the
        <link linkend='var-REQUIRED_DISTRO_FEATURES'><filename>REQUIRED_DISTRO_FEATURES</filename></link>
        and
        <link linkend='var-CONFLICT_DISTRO_FEATURES'><filename>CONFLICT_DISTRO_FEATURES</filename></link>
        variables.
        If any conditions specified in the recipe using the above variables are
        not met, the recipe will be skipped.
    </para>
</section>

<section id='ref-classes-distrodata'>
    <title><filename>distrodata.bbclass</filename></title>

    <para>
        The <filename>distrodata</filename> class
        provides for automatic checking for upstream recipe updates.
    </para>
</section>

<section id='ref-classes-distutils'>
    <title><filename>distutils.bbclass</filename></title>

    <para>
        The <filename>distutils</filename> class supports recipes for Python
        extensions, which are simple.
        These recipes usually only need to point to the source's archive and
        then inherit the proper class.
        Building is split into two methods depending on which method the
        module authors used.
        <itemizedlist>
            <listitem><para>Extensions that use an Autotools-based build system
                require Autotools and
                <filename>distutils</filename>-based classes in their recipes.
                </para></listitem>
            <listitem><para>Extensions that use
                <filename>distutils</filename>-based build systems require
                the <filename>distutils</filename> class in their recipes.
                </para></listitem>
            <listitem><para>Extensions that use the setuptools-based build
                systems require the
                <link linkend='ref-classes-setuptools'><filename>setuptools</filename></link>
                class in their recipes.
                </para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='ref-classes-extrausers'>
    <title><filename>extrausers.bbclass</filename></title>

    <para>
        The <filename>extrausers</filename> class allows
        additional user and group configuration to be applied at the image
        level.
        Inheriting this class either globally or from an image recipe allows
        additional user and group operations to be performed using the
        <link linkend='var-EXTRA_USERS_PARAMS'><filename>EXTRA_USERS_PARAMS</filename></link>
        variable.
        <note>
            The user and group operations added using the
            <filename>extrausers</filename> class are not tied to a specific
            recipe but can be performed across the image as a whole.
            See the
            <link linkend='ref-classes-useradd'><filename>useradd</filename></link>
            class for information on how to add user and group configuration
            to a specific recipe.
        </note>
    </para>

    <para>
        Here is an example that uses this class in an image recipe:
        <literallayout class='monospaced'>
     inherit extrausers
     EXTRA_USERS_PARAMS = "\
         useradd -p '' tester; \
         groupadd developers; \
         userdel nobody; \
         groupdel -g video; \
         groupmod -g 1020 developers; \
         usermod -s /bin/sh tester; \
         "
        </literallayout>
    </para>
</section>

<section id='ref-classes-fontcache'>
    <title><filename>fontcache.bbclass</filename></title>

    <para>
        The <filename>fontcache</filename> class generates the
        proper post-install and post-remove (postinst and postrm)
        scriptlets for font packages.
        These scriptlets call <filename>fc-cache</filename> (part of
        <filename>Fontconfig</filename>) to add the fonts to the font
        information cache.
        Since the cache files are architecture-specific,
        <filename>fc-cache</filename> runs using QEMU if the postinst
        scriptlets need to be run on the build host during image creation.
    </para>

    <para>
        If the fonts being installed are in packages other than the main
        package, set
        <link linkend='var-FONT_PACKAGES'><filename>FONT_PACKAGES</filename></link>
        to include the packages containing the fonts.
    </para>
</section>

<section id='ref-classes-gconf'>
    <title><filename>gconf.bbclass</filename></title>

    <para>
        The <filename>gconf</filename> class provides common
        functionality for recipes that need to install GConf schemas.
        The schemas will be put into a separate package
        (<filename>${</filename><link linkend='var-PN'><filename>PN</filename></link><filename>}-gconf</filename>)
        that is created automatically when this class is inherited.
        This package uses the appropriate post-install and post-remove
        (postinst/postrm) scriptlets to register and unregister the schemas
        in the target image.
    </para>
</section>

<section id='ref-classes-gettext'>
    <title><filename>gettext.bbclass</filename></title>

    <para>
        The <filename>gettext</filename> class provides support for
        building software that uses the GNU <filename>gettext</filename>
        internationalization and localization system.
        All recipes building software that use
        <filename>gettext</filename> should inherit this class.
    </para>
</section>

<section id='ref-classes-gnome'>
    <title><filename>gnome.bbclass</filename></title>

    <para>
        The <filename>gnome</filename> class supports recipes that
        build software from the GNOME stack.
        This class inherits the
        <link linkend='ref-classes-gnomebase'><filename>gnomebase</filename></link>,
        <link linkend='ref-classes-gtk-icon-cache'><filename>gtk-icon-cache</filename></link>,
        <link linkend='ref-classes-gconf'><filename>gconf</filename></link> and
        <link linkend='ref-classes-mime'><filename>mime</filename></link> classes.
        The class also disables GLib Object System (Gobject) introspection
        where applicable.
    </para>
</section>

<section id='ref-classes-gnomebase'>
    <title><filename>gnomebase.bbclass</filename></title>

    <para>
        The <filename>gnomebase</filename> class is the base
        class for recipes that build software from the GNOME stack.
    </para>
</section>

<section id='ref-classes-grub-efi'>
    <title><filename>grub-efi.bbclass</filename></title>

    <para>
        The <filename>grub-efi</filename>
        class provides <filename>grub-efi</filename>-specific functions for
        building bootable images.
    </para>

    <para>
        This class supports several variables:
        <itemizedlist>
            <listitem><para>
                <link linkend='var-INITRD'><filename>INITRD</filename></link>:
                Indicates a filesystem image to use as an initrd (optional).
                </para></listitem>
            <listitem><para>
                <link linkend='var-ROOTFS'><filename>ROOTFS</filename></link>:
                Indicates a filesystem image to include as the root filesystem
                (optional).</para></listitem>
            <listitem><para>
                <link linkend='var-GRUB_GFXSERIAL'><filename>GRUB_GFXSERIAL</filename></link>:
                Set this to "1" to have graphics and serial in the boot menu.
                </para></listitem>
            <listitem><para>
                <link linkend='var-LABELS'><filename>LABELS</filename></link>:
                A list of targets for the automatic configuration.
                </para></listitem>
            <listitem><para>
                <link linkend='var-APPEND'><filename>APPEND</filename></link>:
                An override list of append strings for each
                <filename>LABEL</filename>.
                </para></listitem>
            <listitem><para>
                <link linkend='var-GRUB_OPTS'><filename>GRUB_OPTS</filename></link>:
                Additional options to add to the configuration (optional).
                Options are delimited using semi-colon characters
                (<filename>;</filename>).</para></listitem>
            <listitem><para>
                <link linkend='var-GRUB_TIMEOUT'><filename>GRUB_TIMEOUT</filename></link>:
                Timeout before executing the default <filename>LABEL</filename>
                (optional).
                </para></listitem>
       </itemizedlist>
   </para>
</section>

<section id='ref-classes-gsettings'>
    <title><filename>gsettings.bbclass</filename></title>

    <para>
        The <filename>gsettings</filename> class
        provides common functionality for recipes that need to install
        GSettings (glib) schemas.
        The schemas are assumed to be part of the main package.
        Appropriate post-install and post-remove (postinst/postrm)
        scriptlets are added to register and unregister the schemas in the
        target image.
    </para>
</section>

<section id='ref-classes-gtk-doc'>
    <title><filename>gtk-doc.bbclass</filename></title>

    <para>
        The <filename>gtk-doc</filename> class
        is a helper class to pull in the appropriate
        <filename>gtk-doc</filename> dependencies and disable
        <filename>gtk-doc</filename>.
    </para>
</section>

<section id='ref-classes-gtk-icon-cache'>
    <title><filename>gtk-icon-cache.bbclass</filename></title>

    <para>
        The <filename>gtk-icon-cache</filename> class
        Generates the proper post-install and post-remove (postinst/postrm)
        scriptlets for packages that use GTK+ and install icons.
        These scriptlets call <filename>gtk-update-icon-cache</filename> to add
        the fonts to GTK+'s icon cache.
        Since the cache files are architecture-specific,
        <filename>gtk-update-icon-cache</filename> is run using QEMU if the
        postinst scriptlets need to be run on the build host during image
        creation.
    </para>
</section>

<section id='ref-classes-gtk-immodules-cache'>
    <title><filename>gtk-immodules-cache.bbclass</filename></title>

    <para>
        The <filename>gtk-immodules-cache</filename> class
        generates the proper post-install and post-remove (postinst/postrm)
        scriptlets for packages that install GTK+ input method modules for
        virtual keyboards.
        These scriptlets call <filename>gtk-update-icon-cache</filename> to add
        the input method modules to the cache.
        Since the cache files are architecture-specific,
        <filename>gtk-update-icon-cache</filename> is run using QEMU if the
        postinst scriptlets need to be run on the build host during image
        creation.
    </para>

    <para>
        If the input method modules being installed are in packages other than
        the main package, set
        <link linkend='var-GTKIMMODULES_PACKAGES'><filename>GTKIMMODULES_PACKAGES</filename></link>
        to include the packages containing the modules.
    </para>
</section>

<section id='ref-classes-gzipnative'>
    <title><filename>gzipnative.bbclass</filename></title>

    <para>
        The <filename>gzipnative</filename>
        class enables the use of native versions of <filename>gzip</filename>
        and <filename>pigz</filename> rather than the system versions.
    </para>
</section>

<section id='ref-classes-icecc'>
    <title><filename>icecc.bbclass</filename></title>

    <para>
        The <filename>icecc</filename> class stages directories with symlinks
        from <filename>gcc</filename> and <filename>g++</filename> to
        <filename>icecc</filename>, for both native and cross compilers.
        Depending on each configure or compile, the OpenEmbedded build system
        adds the directories at the head of the <filename>PATH</filename> list
        and then sets
        <link linkend='var-ICECC_CXX'><filename>ICECC_CXX</filename></link>
        and
        <link linkend='var-ICECC_CC'><filename>ICEC_CC</filename></link>.
    </para>

    <para>
        For the cross compiler, the class creates a <filename>tar.gz</filename>
        file that contains the Yocto Project toolchain and sets
        <link linkend='var-ICECC_VERSION'><filename>ICECC_VERSION</filename></link>
        accordingly.
    </para>

    <para>
        The class handles all three different compile stages
        (i.e native ,cross-kernel and target) and creates the necessary
        environment <filename>tar.gz</filename> file to be used by the remote
        machines.
        The class also supports SDK generation.
    </para>

    <para>
        If <link linkend='var-ICECC_PATH'><filename>ICECC_PATH</filename></link>
        is not set in your <filename>local.conf</filename> file, then the
        class tries to locate it using <filename>which</filename>.

        If
        <link linkend='var-ICECC_ENV_EXEC'><filename>ICECC_ENV_EXEC</filename></link>
        is set in your <filename>local.conf</filename> file, the variable should
        point to the <filename>icecc-create-env</filename> script provided by
        the user.
        If you do not point to a user-provided script, the build system
        uses the default script provided by the recipe
        <filename>icecc-create-env.bb</filename>.
        <note>
            This script is a modified version and not the one that comes with
            <filename>icecc</filename>.
        </note>
    </para>

    <para>
        If you do not want the Icecream distributed compile support to apply
        to specific packages or classes, you can effectively "blacklist" them
        by listing the packages and classes using the
        <link linkend='var-ICECC_USER_PACKAGE_BL'><filename>ICECC_USER_PACKAGE_BL</filename></link>
        and
        <link linkend='var-ICECC_USER_CLASS_BL'><filename>ICECC_USER_CLASS_BL</filename></link>,
        variables, respectively, in your <filename>local.conf</filename> file.
        Doing so causes the OpenEmbedded build system to handle these
        compilations locally.
    </para>

    <para>
        Additionally, you can list packages using the
        <link linkend='var-ICECC_USER_PACKAGE_WL'><filename>ICECC_USER_PACKAGE_WL</filename></link>
        variable in your <filename>local.conf</filename> file to force
        <filename>icecc</filename> to be enabled for packages using an empty
        <link linkend='var-PARALLEL_MAKE'><filename>PARALLEL_MAKE</filename></link>
        variable.
    </para>
</section>

<section id='ref-classes-image'>
    <title><filename>image.bbclass</filename></title>

    <para>
        The <filename>image</filename> class helps support creating images
        in different formats.
        First, the root filesystem is created from packages using
        one of the <filename>rootfs_*.bbclass</filename>
        files (depending on the package format used) and then the image is
        created.
        <itemizedlist>
            <listitem><para>The
                <filename><link linkend='var-IMAGE_FSTYPES'>IMAGE_FSTYPES</link></filename>
                variable controls the types of images to generate.
                </para></listitem>
            <listitem><para>The
                <filename><link linkend='var-IMAGE_INSTALL'>IMAGE_INSTALL</link></filename>
                variable controls the list of packages to install into the
                image.</para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='ref-classes-image_types'>
    <title><filename>image_types.bbclass</filename></title>

    <para>
        The <filename>image_types</filename> class defines all of
        the standard image output types that you can enable through the
        <link linkend='var-IMAGE_FSTYPES'><filename>IMAGE_FSTYPES</filename></link>
        variable.
        You can use this class as a reference on how to add support for custom
        image output types.
    </para>

    <para>
        By default, this class is enabled through the
        <link linkend='var-IMAGE_CLASSES'><filename>IMAGE_CLASSES</filename></link>
        variable in
        <link linkend='ref-classes-image'><filename>image.bbclass</filename></link>.
        If you define your own image types using a custom BitBake class and
        then use <filename>IMAGE_CLASSES</filename> to enable it, the custom
        class must either inherit <filename>image_types</filename> or
        <filename>image_types</filename> must also appear in
        <filename>IMAGE_CLASSES</filename>.
    </para>
</section>

<section id='ref-classes-image_types_uboot'>
    <title><filename>image_types_uboot.bbclass</filename></title>

    <para>
        The <filename>image_types_uboot</filename> class
        defines additional image types specifically for the U-Boot bootloader.
    </para>
</section>

<section id='ref-classes-image-live'>
    <title><filename>image-live.bbclass</filename></title>

    <para>
        The <filename>image-live</filename> class supports building "live"
        images.
        Normally, you do not use this class directly.
        Instead, you add "live" to
        <link linkend='var-IMAGE_FSTYPES'><filename>IMAGE_FSTYPES</filename></link>.
    </para>
</section>

<section id='ref-classes-image-mklibs'>
    <title><filename>image-mklibs.bbclass</filename></title>

    <para>
        The <filename>mklibs</filename> class
        enables the use of the <filename>mklibs</filename> utility during the
        <filename>do_rootfs</filename> task, which optimizes the size of
        libraries contained in the image.
    </para>

    <para>
        The
        <link linkend='var-USER_CLASSES'><filename>USER_CLASSES</filename></link>
        variable enables this class.
        By default, the class is enabled in the
        <filename>local.conf.template</filename> in the
        <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>
        as follows:
        <literallayout class='monospaced'>
     USER_CLASSES ?= "buildstats image-mklibs image-prelink"
        </literallayout>
    </para>
</section>

<section id='ref-classes-image-prelink'>
    <title><filename>image-prelink.bbclass</filename></title>

    <para>
        The <filename>image-prelink</filename> class
        enables the use of the <filename>prelink</filename> utility during
        the <filename>do_rootfs</filename> task, which optimizes the dynamic
        linking of shared libraries to reduce executable startup time.
    </para>

    <para>
        The
        <link linkend='var-USER_CLASSES'><filename>USER_CLASSES</filename></link>
        variable enables this class.
        By default, the class is enabled in the
        <filename>local.conf.template</filename> in the
        <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>
        as follows:
        <literallayout class='monospaced'>
     USER_CLASSES ?= "buildstats image-mklibs image-prelink"
        </literallayout>
    </para>
</section>

<section id='ref-classes-image-swab'>
    <title><filename>image-swab.bbclass</filename></title>

    <para>
        The <filename>image-swab</filename> class enables the
        <ulink url='&YOCTO_HOME_URL;/tools-resources/projects/swabber'>Swabber</ulink>
        tool in order to detect and log accesses to the host system during
        the OpenEmbedded build process.
        <note>
            This class is currently unmaintained.
        </note>
    </para>
</section>

<section id='ref-classes-image-vmdk'>
    <title><filename>image-vmdk.bbclass</filename></title>

    <para>
        The <filename>image-vmdk</filename> class supports building VMware
        VMDK images.
        Normally, you do not use this class directly.
        Instead, you add "vmdk" to
        <link linkend='var-IMAGE_FSTYPES'><filename>IMAGE_FSTYPES</filename></link>.
    </para>
</section>

<section id='ref-classes-insane'>
    <title><filename>insane.bbclass</filename></title>

    <para>
        The <filename>insane</filename> class adds a step to the package
        generation process so that output quality assurance checks are
        generated by the OpenEmbedded build system.
        A range of checks are performed that check the build's output
        for common problems that show up during runtime.
        Distribution policy usually dictates whether to include this class.
    </para>

    <para>
        You can configure the sanity checks so that specific test failures
        either raise a warning or an error message.
        Typically, failures for new tests generate a warning.
        Subsequent failures for the same test would then generate an error
        message once the metadata is in a known and good condition.
    </para>

    <para>
        Use the
        <link linkend='var-WARN_QA'><filename>WARN_QA</filename></link> and
        <link linkend='var-ERROR_QA'><filename>ERROR_QA</filename></link>
         variables to control the behavior of
        these checks at the global level (i.e. in your custom distro
        configuration).
        However, to skip one or more checks in recipes, you should use
        <link linkend='var-INSANE_SKIP'><filename>INSANE_SKIP</filename></link>.
        For example, to skip the check for symbolic link
        <filename>.so</filename> files in the main package of a recipe,
        add the following to the recipe.
        You need to realize that the package name override, in this example
        <filename>${PN}</filename>, must be used:
        <literallayout class='monospaced'>
     INSANE_SKIP_${PN} += "dev-so"
        </literallayout>
        Please keep in mind that the QA checks exist in order to detect real
        or potential problems in the packaged output.
        So exercise caution when disabling these checks.
    </para>

    <para>
        The following list shows the tests you can list with the
        <filename>WARN_QA</filename> and <filename>ERROR_QA</filename>
        variables:
        <itemizedlist>
            <listitem><para><emphasis><filename>ldflags:</filename></emphasis>
                Ensures that the binaries were linked with the
                <filename>LDFLAGS</filename> options provided by the build system.
                If this test fails, check that the <filename>LDFLAGS</filename> variable
                is being passed to the linker command.</para></listitem>
            <listitem><para><emphasis><filename>useless-rpaths:</filename></emphasis>
                Checks for dynamic library load paths (rpaths) in the binaries that
                by default on a standard system are searched by the linker (e.g.
                <filename>/lib</filename> and <filename>/usr/lib</filename>).
                While these paths will not cause any breakage, they do waste space and
                are unnecessary.</para></listitem>
            <listitem><para><emphasis><filename>rpaths:</filename></emphasis>
                Checks for rpaths in the binaries that contain build system paths such
                as <filename>TMPDIR</filename>.
                If this test fails, bad <filename>-rpath</filename> options are being
                passed to the linker commands and your binaries have potential security
                issues.</para></listitem>
            <listitem><para><emphasis><filename>dev-so:</filename></emphasis>
                Checks that the <filename>.so</filename> symbolic links are in the
                <filename>-dev</filename> package and not in any of the other packages.
                In general, these symlinks are only useful for development purposes.
                Thus, the <filename>-dev</filename> package is the correct location for
                them.
                Some very rare cases do exist for dynamically loaded modules where
                these symlinks are needed instead in the main package.
                </para></listitem>
            <listitem><para><emphasis><filename>debug-files:</filename></emphasis>
                Checks for <filename>.debug</filename> directories in anything but the
                <filename>-dbg</filename> package.
                The debug files should all be in the <filename>-dbg</filename> package.
                Thus, anything packaged elsewhere is incorrect packaging.</para></listitem>
            <listitem><para><emphasis><filename>arch:</filename></emphasis>
                Checks the Executable and Linkable Format (ELF) type, bit size, and endianness
                of any binaries to ensure they match the target architecture.
                This test fails if any binaries don't match the type since there would be an
                incompatibility.
                Sometimes software, like bootloaders, might need to bypass this check.
                </para></listitem>
            <listitem><para><emphasis><filename>debug-deps:</filename></emphasis>
                Checks that <filename>-dbg</filename> packages only depend on other
                <filename>-dbg</filename> packages and not on any other types of packages,
                which would cause a packaging bug.</para></listitem>
            <listitem><para><emphasis><filename>dev-deps:</filename></emphasis>
                Checks that <filename>-dev</filename> packages only depend on other
                <filename>-dev</filename> packages and not on any other types of packages,
                which would be a packaging bug.</para></listitem>
            <listitem><para><emphasis><filename>pkgconfig:</filename></emphasis>
                Checks <filename>.pc</filename> files for any
                <link linkend='var-TMPDIR'><filename>TMPDIR</filename></link>/<link linkend='var-WORKDIR'><filename>WORKDIR</filename></link>
                paths.
                Any <filename>.pc</filename> file containing these paths is incorrect
                since <filename>pkg-config</filename> itself adds the correct sysroot prefix
                when the files are accessed.</para></listitem>
            <listitem><para><emphasis><filename>textrel:</filename></emphasis>
                Checks for ELF binaries that contain relocations in their
                <filename>.text</filename> sections, which can result in a
                performance impact at runtime.</para></listitem>
            <listitem><para><emphasis><filename>pkgvarcheck:</filename></emphasis>
                Checks through the variables
                <link linkend='var-RDEPENDS'><filename>RDEPENDS</filename></link>,
                <link linkend='var-RRECOMMENDS'><filename>RRECOMMENDS</filename></link>,
                <link linkend='var-RSUGGESTS'><filename>RSUGGESTS</filename></link>,
                <link linkend='var-RCONFLICTS'><filename>RCONFLICTS</filename></link>,
                <link linkend='var-RPROVIDES'><filename>RPROVIDES</filename></link>,
                <link linkend='var-RREPLACES'><filename>RREPLACES</filename></link>,
                <link linkend='var-FILES'><filename>FILES</filename></link>,
                <link linkend='var-ALLOW_EMPTY'><filename>ALLOW_EMPTY</filename></link>,
                <filename>pkg_preinst</filename>,
                <filename>pkg_postinst</filename>,
                <filename>pkg_prerm</filename>
                and <filename>pkg_postrm</filename>, and reports if there are
                variable sets that are not package-specific.
                Using these variables without a package suffix is bad practice,
                and might unnecessarily complicate dependencies of other packages
                within the same recipe or have other unintended consequences.
                </para></listitem>
            <listitem><para><emphasis><filename>xorg-driver-abi:</filename></emphasis>
                Checks that all packages containing Xorg drivers have ABI
                dependencies.
                The <filename>xserver-xorg</filename> recipe provides driver
                ABI names.
                All drivers should depend on the ABI versions that they have
                been built against.
                Driver recipes that include
                <filename>xorg-driver-input.inc</filename>
                or <filename>xorg-driver-video.inc</filename> will
                automatically get these versions.
                Consequently, you should only need to explicitly add
                dependencies to binary driver recipes.
                </para></listitem>
            <listitem><para><emphasis><filename>libexec:</filename></emphasis>
                Checks if a package contains files in
                <filename>/usr/libexec</filename>.
                This check is not performed if the
                <filename>libexecdir</filename> variable has been set
                explicitly to <filename>/usr/libexec</filename>.
                </para></listitem>
            <listitem><para><emphasis><filename>staticdev:</filename></emphasis>
                Checks for static library files (<filename>*.a</filename>) in
                non-<filename>staticdev</filename> packages.
                </para></listitem>
            <listitem><para><emphasis><filename>la:</filename></emphasis>
                Checks <filename>.la</filename> files for any <filename>TMPDIR</filename>
                paths.
                Any <filename>.la</filename> file containing these paths is incorrect since
                <filename>libtool</filename> adds the correct sysroot prefix when using the
                files automatically itself.</para></listitem>
            <listitem><para><emphasis><filename>desktop:</filename></emphasis>
                Runs the <filename>desktop-file-validate</filename> program
                against any <filename>.desktop</filename> files to validate
                their contents against the specification for
                <filename>.desktop</filename> files.</para></listitem>
            <listitem><para><emphasis><filename>already-stripped:</filename></emphasis>
                Checks that produced binaries have not already been
                stripped prior to the build system extracting debug symbols.
                It is common for upstream software projects to default to
                stripping debug symbols for output binaries.
                In order for debugging to work on the target using
                <filename>-dbg</filename> packages, this stripping must be
                disabled.
                </para></listitem>
            <listitem><para><emphasis><filename>split-strip:</filename></emphasis>
                Reports that splitting or stripping debug symbols from binaries
                has failed.
                </para></listitem>
            <listitem><para><emphasis><filename>arch:</filename></emphasis>
                Checks to ensure the architecture, bit size, and endianness
                of all output binaries matches that of the target.
                This test can detect when the wrong compiler or compiler options
                have been used.
                </para></listitem>
            <listitem><para><emphasis><filename>installed-vs-shipped:</filename></emphasis>
                Reports when files have been installed within
                <filename>do_install</filename> but have not been included in
                any package by way of the
                <link linkend='var-FILES'><filename>FILES</filename></link>
                variable.
                Files that do not appear in any package cannot be present in
                an image later on in the build process.
                Ideally, all installed files should be packaged or not
                installed at all.
                These files can be deleted at the end of
                <filename>do_install</filename> if the files are not
                needed in any package.
                </para></listitem>
            <listitem><para><emphasis><filename>dep-cmp:</filename></emphasis>
                Checks for invalid version comparison statements in runtime
                dependency relationships between packages (i.e. in
                <link linkend='var-RDEPENDS'><filename>RDEPENDS</filename></link>,
                <link linkend='var-RRECOMMENDS'><filename>RRECOMMENDS</filename></link>,
                <link linkend='var-RSUGGESTS'><filename>RSUGGESTS</filename></link>,
                <link linkend='var-RPROVIDES'><filename>RPROVIDES</filename></link>,
                <link linkend='var-RREPLACES'><filename>RREPLACES</filename></link>,
                and
                <link linkend='var-RCONFLICTS'><filename>RCONFLICTS</filename></link>
                variable values).
                Any invalid comparisons might trigger failures or undesirable
                behavior when passed to the package manager.
                </para></listitem>
            <listitem><para><emphasis><filename>files-invalid:</filename></emphasis>
                Checks for
                <link linkend='var-FILES'><filename>FILES</filename></link>
                variable values that contain "//", which is invalid.
                </para></listitem>
            <listitem><para><emphasis><filename>incompatible-license:</filename></emphasis>
                Report when packages are excluded from being created due to
                being marked with a license that is in
                <link linkend='var-INCOMPATIBLE_LICENSE'><filename>INCOMPATIBLE_LICENSE</filename></link>.
                </para></listitem>
            <listitem><para><emphasis><filename>compile-host-path:</filename></emphasis>
                Checks the <filename>do_compile</filename> log for indications
                that paths to locations on the build host were used.
                Using such paths might result in host contamination of the
                build output.
                </para></listitem>
            <listitem><para><emphasis><filename>install-host-path:</filename></emphasis>
                Checks the <filename>do_install</filename> log for indications
                that paths to locations on the build host were used.
                Using such paths might result in host contamination of the
                build output.
                </para></listitem>
            <listitem><para><emphasis><filename>libdir:</filename></emphasis>
                Checks for libraries being installed into incorrect
                (possibly hardcoded) installation paths.
                For example, this test will catch recipes that install
                <filename>/lib/bar.so</filename> when
                <filename>${base_libdir}</filename> is "lib32".
                Another example is when recipes install
                <filename>/usr/lib64/foo.so</filename> when
                <filename>${libdir}</filename> is "/usr/lib".
                </para></listitem>
            <listitem><para><emphasis><filename>packages-list:</filename></emphasis>
                Checks for the same package being listed multiple times through
                the <link linkend='var-PACKAGES'><filename>PACKAGES</filename></link>
                variable value.
                Installing the package in this manner can cause errors during
                packaging.
                </para></listitem>
            <listitem><para><emphasis><filename>perm-config:</filename></emphasis>
                Reports lines in <filename>fs-perms.txt</filename> that have
                an invalid format.
                </para></listitem>
            <listitem><para><emphasis><filename>perm-line:</filename></emphasis>
                Reports lines in <filename>fs-perms.txt</filename> that have
                an invalid format.
                </para></listitem>
            <listitem><para><emphasis><filename>perm-link:</filename></emphasis>
                Reports lines in <filename>fs-perms.txt</filename> that
                specify 'link' where the specified target already exists.
                </para></listitem>
            <listitem><para><emphasis><filename>pkgname:</filename></emphasis>
                Checks that all packages in
                <link linkend='var-PACKAGES'><filename>PACKAGES</filename></link>
                have names that do not contain invalid characters (i.e.
                characters other than 0-9, a-z, ., +, and -).
                </para></listitem>
            <listitem><para><emphasis><filename>pn-overrides:</filename></emphasis>
                Checks that a recipe does not have a name
                (<link linkend='var-PN'><filename>PN</filename></link>) value
                that appears in
                <link linkend='var-OVERRIDES'><filename>OVERRIDES</filename></link>.
                If a recipe is named such that its <filename>PN</filename>
                value matches something already in
                <filename>OVERRIDES</filename> (e.g. <filename>PN</filename>
                happens to be the same as
                <link linkend='var-MACHINE'><filename>MACHINE</filename></link>
                or
                <link linkend='var-DISTRO'><filename>DISTRO</filename></link>),
                it can have unexpected consequences.
                For example, assignments such as
                <filename>FILES_${PN} = "xyz"</filename> effectively turn into
                <filename>FILES = "xyz"</filename>.
                </para></listitem>
            <listitem><para><emphasis><filename>unsafe-references-in-binaries:</filename></emphasis>
                Reports when a binary installed in
                <filename>${base_libdir}</filename>,
                <filename>${base_bindir}</filename>, or
                <filename>${base_sbindir}</filename>, depends on another
                binary installed under <filename>${exec_prefix}</filename>.
                This dependency is a concern if you want the system to remain
                basically operable if <filename>/usr</filename> is mounted
                separately and is not mounted.
                <note>
                    Defaults for binaries installed in
                    <filename>${base_libdir}</filename>,
                    <filename>${base_bindir}</filename>, and
                    <filename>${base_sbindir}</filename> are
                    <filename>/lib</filename>, <filename>/bin</filename>, and
                    <filename>/sbin</filename>, respectively.
                    The default for a binary installed
                    under <filename>${exec_prefix}</filename> is
                    <filename>/usr</filename>.
                </note>
                </para></listitem>
            <listitem><para><emphasis><filename>unsafe-references-in-scripts:</filename></emphasis>
                Reports when a script file installed in
                <filename>${base_libdir}</filename>,
                <filename>${base_bindir}</filename>, or
                <filename>${base_sbindir}</filename>, depends on files
                installed under <filename>${exec_prefix}</filename>.
                This dependency is a concern if you want the system to remain
                basically operable if <filename>/usr</filename> is mounted
                separately and is not mounted.
                <note>
                    Defaults for binaries installed in
                    <filename>${base_libdir}</filename>,
                    <filename>${base_bindir}</filename>, and
                    <filename>${base_sbindir}</filename> are
                    <filename>/lib</filename>, <filename>/bin</filename>, and
                    <filename>/sbin</filename>, respectively.
                    The default for a binary installed
                    under <filename>${exec_prefix}</filename> is
                    <filename>/usr</filename>.
                </note>
                </para></listitem>
            <listitem><para><emphasis><filename>var-undefined:</filename></emphasis>
                Reports when variables fundamental to packaging (i.e.
                <link linkend='var-WORKDIR'><filename>WORKDIR</filename></link>,
                <link linkend='var-DEPLOY_DIR'><filename>DEPLOY_DIR</filename></link>,
                <link linkend='var-D'><filename>D</filename></link>,
                <link linkend='var-PN'><filename>PN</filename></link>, and
                <link linkend='var-PKGD'><filename>PKGD</filename></link>) are
                undefined during <filename>do_package</filename>.
                </para></listitem>
            <listitem><para><emphasis><filename>pkgv-undefined:</filename></emphasis>
                Checks to see if the <filename>PKGV</filename> variable
                is undefined during <filename>do_package</filename>.
                </para></listitem>
            <listitem><para><emphasis><filename>buildpaths:</filename></emphasis>
                Checks for paths to locations on the build host inside the
                output files.
                Currently, this test triggers too many false positives and
                thus is not normally enabled.
                </para></listitem>
            <listitem><para><emphasis><filename>perms:</filename></emphasis>
                Currently, this check is unused but reserved.
                </para></listitem>
            <listitem><para><emphasis><filename>version-going-backwards:</filename></emphasis>
                If Build History is enabled, reports when a package
                being written out has a lower version than the previously
                written package under the same name.
                If you are placing output packages into a feed and
                upgrading packages on a target system using that feed, the
                version of a package going backwards can result in the target
                system not correctly upgrading to the "new" version of the
                package.
                <note>
                    If you are not using runtime package management on your
                    target system, then you do not need to worry about
                    this situation.
                </note>
                </para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='ref-classes-insserve'>
    <title><filename>insserve.bbclass</filename></title>

    <para>
        The <filename>insserve</filename> class
        uses the <filename>insserv</filename> utility to update the order of
        symbolic links in <filename>/etc/rc?.d/</filename> within an image
        based on dependencies specified by LSB headers in the
        <filename>init.d</filename> scripts themselves.
    </para>
</section>

<section id='ref-classes-kernel'>
    <title><filename>kernel.bbclass</filename></title>

    <para>
        The <filename>kernel</filename> class handles building Linux kernels.
        The class contains code to build all kernel trees.
        All needed headers are staged into the
        <filename><link linkend='var-STAGING_KERNEL_DIR'>STAGING_KERNEL_DIR</link></filename>
        directory to allow out-of-tree module builds using <filename>module.bbclass</filename>.
    </para>

    <para>
        This means that each built kernel module is packaged separately and inter-module
        dependencies are created by parsing the <filename>modinfo</filename> output.
        If all modules are required, then installing the <filename>kernel-modules</filename>
        package installs all packages with modules and various other kernel packages
        such as <filename>kernel-vmlinux</filename>.
    </para>

    <para>
        Various other classes are used by the kernel and module classes internally including
        <filename>kernel-arch.bbclass</filename>, <filename>module_strip.bbclass</filename>,
        <filename>module-base.bbclass</filename>, and <filename>linux-kernel-base.bbclass</filename>.
    </para>
</section>

<section id='ref-classes-kernel-arch'>
    <title><filename>kernel-arch.bbclass</filename></title>

    <para>
        The <filename>kernel-arch</filename> class
        sets the <filename>ARCH</filename> environment variable for Linux
        kernel compilation (including modules).
    </para>
</section>

<section id='ref-classes-kernel-module-split'>
    <title><filename>kernel-module-split.bbclass</filename></title>

    <para>
        The <filename>kernel-module-split</filename> class
        provides common functionality for splitting Linux kernel modules into
        separate packages.
    </para>
</section>

<section id='ref-classes-kernel-yocto'>
    <title><filename>kernel-yocto.bbclass</filename></title>

    <para>
        The <filename>kernel-yocto</filename> class
        provides common functionality for building from linux-yocto style
        kernel source repositories.
    </para>
</section>

<section id='ref-classes-lib_package'>
    <title><filename>lib_package.bbclass</filename></title>

    <para>
        The <filename>lib_package</filename> class
        supports recipes that build libraries and produce executable
        binaries, where those binaries should not be installed by default
        along with the library.
        Instead, the binaries are added to a separate
        <filename>${</filename><link linkend='var-PN'><filename>PN</filename></link><filename>}-bin</filename>
        package to make their installation optional.
    </para>
</section>

<section id='ref-classes-license'>
    <title><filename>license.bbclass</filename></title>

    <para>
        The <filename>license</filename> class provides license
        manifest creation and license exclusion.
        This class is enabled by default using the default value for the
        <link linkend='var-INHERIT_DISTRO'><filename>INHERIT_DISTRO</filename></link>
        variable.
    </para>
</section>

<section id='ref-classes-linux-kernel-base'>
    <title><filename>linux-kernel-base.bbclass</filename></title>

    <para>
        The <filename>linux-kernel-base</filename> class
        provides common functionality for recipes that build out of the Linux
        kernel source tree.
        These builds goes beyond the kernel itself.
        For example, the Perf recipe also inherits this class.
    </para>
</section>

<section id='ref-classes-logging'>
    <title><filename>logging.bbclass</filename></title>

    <para>
        The <filename>logging</filename> class provides the standard
        shell functions used to log messages for various BitBake severity levels
        (i.e. <filename>bbplain</filename>, <filename>bbnote</filename>,
        <filename>bbwarn</filename>, <filename>bberror</filename>,
        <filename>bbfatal</filename>, and <filename>bbdebug</filename>.
    </para>

    <para>
        This class is enabled by default since it is inherited by
        the <filename>base</filename> class.
    </para>
</section>

<section id='ref-classes-meta'>
    <title><filename>meta.bbclass</filename></title>

    <para>
        The <filename>meta</filename> class is inherited by recipes
        that do not build any output packages themselves, but act as a "meta"
        target for building other recipes.
    </para>
</section>

<section id='ref-classes-metadata_scm'>
    <title><filename>metadata_scm.bbclass</filename></title>

    <para>
        The <filename>metadata_scm</filename> class provides functionality for
        querying the branch and revision of a Source Code Manager (SCM)
        repository.
    </para>

    <para>
        The <link linkend='ref-classes-base'><filename>base</filename></link>
        class uses this class to print the revisions of each layer before
        starting every build.
        The <filename>metadata_scm</filename> class is enabled by default
        because it is inherited by the <filename>base</filename> class.
    </para>
</section>

<section id='ref-classes-mime'>
    <title><filename>mime.bbclass</filename></title>

    <para>
        The <filename>mime</filename> class generates the proper
        post-install and post-remove (postinst/postrm) scriptlets for packages
        that install MIME type files.
        These scriptlets call <filename>update-mime-database</filename> to add
        the MIME types to the shared database.
    </para>
</section>

<section id='ref-classes-mirrors'>
    <title><filename>mirrors.bbclass</filename></title>

    <para>
        The <filename>mirrors</filename> class sets up some standard
        <link linkend='var-MIRRORS'><filename>MIRRORS</filename></link> entries
        for source code mirrors.
        These mirrors provide a fall-back path in case the upstream source
        specified in
        <link linkend='var-SRC_URI'><filename>SRC_URI</filename></link>
        within recipes is unavailable.
    </para>

    <para>
        This class is enabled by default since it is inherited by the
        <link linkend='ref-classes-base'><filename>base</filename></link> class.
    </para>
</section>

<section id='ref-classes-multilib*'>
    <title><filename>multilib*.bbclass</filename></title>

    <para>
        The <filename>multilib*</filename> classes provide support
        for building libraries with different target optimizations or target
        architectures and installing them side-by-side in the same image.
    </para>

    <para>
        For more information on using the Multilib feature, see the
        "<ulink url='&YOCTO_DOCS_DEV_URL;#combining-multiple-versions-library-files-into-one-image'>Combining Multiple Versions of Library Files into One Image</ulink>"
        section in the Yocto Project Development Manual.
    </para>
</section>

<section id='ref-classes-native'>
    <title><filename>native.bbclass</filename></title>

    <para>
        The <filename>native</filename> class provides common
        functionality for recipes that wish to build tools to run on the build
        host (i.e. tools that use the compiler or other tools from the
        build host).
    </para>

    <para>
        You can create a recipe that builds tools that run natively on the
        host a couple different ways:
        <itemizedlist>
            <listitem><para>Create a <filename>myrecipe-native.bb</filename>
                that inherits the <filename>native</filename> class.
                </para></listitem>
            <listitem><para>Create or modify a target recipe that has adds
                the following:
                <literallayout class='monospaced'>
     <link linkend='var-BBCLASSEXTEND'><filename>BBCLASSEXTEND</filename></link> = "native"
                </literallayout>
                Inside the recipe, use <filename>_class-native</filename> and
                <filename>_class-target</filename> overrides to specify any
                functionality specific to the respective native or target
                case.</para></listitem>
        </itemizedlist>
    </para>

    <para>
        Although applied differently, the <filename>native</filename> class is
        used with both methods.
        The advantage of the second method is that you do not need to have two
        separate recipes (assuming you need both) for native and target.
        All common parts of the recipe are automatically shared.
    </para>
</section>

<section id='ref-classes-nativesdk'>
    <title><filename>nativesdk.bbclass</filename></title>

    <para>
        The <filename>nativesdk</filename> class provides common
        functionality for recipes that wish to build tools to run as part of
        an SDK (i.e. tools that run on
        <link linkend='var-SDKMACHINE'><filename>SDKMACHINE</filename></link>).
    </para>

    <para>
        You can create a recipe that builds tools that run on the SDK machine
        a couple different ways:
        <itemizedlist>
            <listitem><para>Create a <filename>myrecipe-native.bb</filename>
                recipe that inherits the <filename>nativesdk</filename> class.
                </para></listitem>
            <listitem><para>Create a <filename>nativesdk</filename> variant
                of any recipe by adding the following:
                <literallayout class='monospaced'>
     <link linkend='var-BBCLASSEXTEND'><filename>BBCLASSEXTEND</filename></link> = "nativesdk"
                </literallayout>
                Inside the recipe, use <filename>_class-nativesdk</filename> and
                <filename>_class-target</filename> overrides to specify any
                functionality specific to the respective SDK machine or target
                case.</para></listitem>
        </itemizedlist>
    </para>

    <para>
        Although applied differently, the <filename>nativesdk</filename> class
        is used with both methods.
        The advantage of the second method is that you do not need to have two
        separate recipes (assuming you need both) for the SDK machine and the
        target.
        All common parts of the recipe are automatically shared.
    </para>
</section>

<section id='ref-classes-oelint'>
    <title><filename>oelint.bbclass</filename></title>

    <para>
        The <filename>oelint</filename> class is an
        obsolete lint checking tool that exists in
        <filename>meta/classes</filename> in the
        <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>.
    </para>

    <para>
        A number of classes exist that are could be generally useful in
        OE-Core but are never actually used within OE-Core itself.
        The <filename>oelint</filename> class is one such example.
        However, being aware of this class can reduce the proliferation of
        different versions of similar classes across multiple layers.
    </para>
</section>

<section id='ref-classes-ownmirrors'>
    <title><filename>ownmirrors.bbclass</filename></title>

    <para>
        The <filename>ownmirrors</filename> class makes it
        easier to set up your own
        <link linkend='var-PREMIRRORS'><filename>PREMIRRORS</filename></link>
        from which to first fetch source before attempting to fetch it from the
        upstream specified in
        <link linkend='var-SRC_URI'><filename>SRC_URI</filename></link>
        within each recipe.
    </para>

    <para>
        To use this class, inherit it globally and specify
        <link linkend='var-SOURCE_MIRROR_URL'><filename>SOURCE_MIRROR_URL</filename></link>.
        Here is an example:
        <literallayout class='monospaced'>
     INHERIT += "own-mirrors"
     SOURCE_MIRROR_URL = "http://example.com/my-source-mirror"
        </literallayout>
        You can specify only a single URL in
        <filename>SOURCE_MIRROR_URL</filename>.
    </para>
</section>

<section id='ref-classes-package'>
    <title><filename>package.bbclass</filename></title>

    <para>
        The <filename>package</filename> supports generating
        packages from a build's output.
        The core generic functionality is in
        <filename>package.bbclass</filename>.
        The code specific to particular package types resides in these
        package-specific classes:
        <link linkend='ref-classes-package_deb'><filename>package_deb</filename></link>,
        <link linkend='ref-classes-package_rpm'><filename>package_rpm</filename></link>,
        <link linkend='ref-classes-package_ipk'><filename>package_ipk</filename></link>,
        and
        <link linkend='ref-classes-package_tar'><filename>package_tar</filename></link>.
    </para>

    <para>
        You can control the list of resulting package formats by using the
        <filename><link linkend='var-PACKAGE_CLASSES'>PACKAGE_CLASSES</link></filename>
        variable defined in your <filename>conf/local.conf</filename>
        configuration file, which is located in the
        <ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>.
        When defining the variable, you can specify one or more package types.
        Since images are generated from packages, a packaging class is
        needed to enable image generation.
        The first class listed in this variable is used for image generation.
    </para>

    <para>
        If you take the optional step to set up a repository (package feed)
        on the development host that can be used by Smart, you can
        install packages from the feed while you are running the image
        on the target (i.e. runtime installation of packages).
        For more information, see the
        "<ulink url='&YOCTO_DOCS_DEV_URL;#using-runtime-package-management'>Using Runtime Package Management</ulink>"
         section in the Yocto Project Development Manual.
    </para>

    <para>
        The package-specific class you choose can affect build-time performance
        and has space ramifications.
        In general, building a package with IPK takes about thirty percent less
        time as compared to using RPM to build the same or similar package.
        This comparison takes into account a complete build of the package with
        all dependencies previously built.
        The reason for this discrepancy is because the RPM package manager
        creates and processes more
        <ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink> than the
        IPK package manager.
        Consequently, you might consider setting
        <filename>PACKAGE_CLASSES</filename> to "package_ipk" if you are
        building smaller systems.
    </para>

    <para>
        Before making your package manager decision, however, you should
        consider some further things about using RPM:
        <itemizedlist>
            <listitem><para>
                RPM starts to provide more abilities than IPK due to
                the fact that it processes more Metadata.
                For example, this information includes individual file types,
                file checksum generation and evaluation on install, sparse file
                support, conflict detection and resolution for Multilib systems,
                ACID style upgrade, and repackaging abilities for rollbacks.
                </para></listitem>
            <listitem><para>
                For smaller systems, the extra space used for the Berkley
                Database and the amount of metadata when using RPM can affect
                your ability to perform on-device upgrades.
                </para></listitem>
        </itemizedlist>
    </para>

    <para>
        You can find additional information on the effects of the package
        class at these two Yocto Project mailing list links:
        <itemizedlist>
            <listitem><para><ulink url='&YOCTO_LISTS_URL;/pipermail/poky/2011-May/006362.html'>
                https://lists.yoctoproject.org/pipermail/poky/2011-May/006362.html</ulink></para></listitem>
            <listitem><para><ulink url='&YOCTO_LISTS_URL;/pipermail/poky/2011-May/006363.html'>
                https://lists.yoctoproject.org/pipermail/poky/2011-May/006363.html</ulink></para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='ref-classes-package_deb'>
    <title><filename>package_deb.bbclass</filename></title>

    <para>
        The <filename>package_deb</filename> class
        provides support for creating packages that use the
        <filename>.deb</filename> file format.
        The class ensures the packages are written out to the
        <filename>${</filename><link linkend='var-DEPLOY_DIR'><filename>DEPLOY_DIR</filename></link><filename>}/deb</filename>
        directory in a <filename>.deb</filename> file format.
        <note>
            This package inherits the
            <link linkend='ref-classes-package'><filename>package</filename></link>
            class.
        </note>
    </para>
</section>

<section id='ref-classes-package_ipk'>
    <title><filename>package_ipk.bbclass</filename></title>

    <para>
        The <filename>package_ipk</filename> class
        provides support for creating packages that use the
        <filename>.ipk</filename> file format.
        The class ensures the packages are written out to the
        <filename>${</filename><link linkend='var-DEPLOY_DIR'><filename>DEPLOY_DIR</filename></link><filename>}/ipk</filename>
        directory in a <filename>.ipk</filename> file format.
        <note>
            This package inherits the
            <link linkend='ref-classes-package'><filename>package</filename></link>
            class.
        </note>
    </para>
</section>

<section id='ref-classes-package_rpm'>
    <title><filename>package_rpm.bbclass</filename></title>

    <para>
        The <filename>package_deb</filename> class
        provides support for creating packages that use the
        <filename>.rpm</filename> file format.
        The class ensures the packages are written out to the
        <filename>${</filename><link linkend='var-DEPLOY_DIR'><filename>DEPLOY_DIR</filename></link><filename>}/rpm</filename>
        directory in a <filename>.rpm</filename> file format.
        <note>
            This package inherits the
            <link linkend='ref-classes-package'><filename>package</filename></link>
            class.
        </note>
    </para>
</section>

<section id='ref-classes-package_tar'>
    <title><filename>package_tar.bbclass</filename></title>

    <para>
        The <filename>package_tar</filename>
        class provides support for creating packages that use the
        <filename>.tar</filename> file format.
        The class ensures the packages are written out to the
        <filename>${</filename><link linkend='var-DEPLOY_DIR'><filename>DEPLOY_DIR</filename></link><filename>}/tar</filename>
        directory in a <filename>.tar</filename> file format.
        <note>
            This package inherits the
            <link linkend='ref-classes-package'><filename>package</filename></link>
            class.
        </note>
    </para>
</section>

<section id='ref-classes-packagedata'>
    <title><filename>packagedata.bbclass</filename></title>

    <para>
        The <filename>packagedata</filename> class provides
        common functionality for reading <filename>pkgdata</filename> files
        found in
        <link linkend='var-PKGDATA_DIR'><filename>PKGDATA_DIR</filename></link>.
        These files contain information about each output package produced by
        the OpenEmbedded build system.
    </para>

    <para>
        This class is enabled by default because it is inherited by the
        <link linkend='ref-classes-package'><filename>package</filename></link>
        class.
    </para>
</section>

<section id='ref-classes-packagegroup'>
    <title><filename>packagegroup.bbclass</filename></title>

    <para>
        The <filename>packagegroup</filename> class sets default values
        appropriate for package group recipes (e.g.
        <filename><link linkend='var-PACKAGES'>PACKAGES</link></filename>,
        <filename><link linkend='var-PACKAGE_ARCH'>PACKAGE_ARCH</link></filename>,
        <filename><link linkend='var-ALLOW_EMPTY'>ALLOW_EMPTY</link></filename>,
        and so forth).
        It is highly recommended that all package group recipes inherit this class.
    </para>

    <para>
        For information on how to use this class, see the
        "<ulink url='&YOCTO_DOCS_DEV_URL;#usingpoky-extend-customimage-customtasks'>Customizing Images Using Custom Package Groups</ulink>"
        section in the Yocto Project Development Manual.
    </para>

    <para>
        Previously, this class was called the <filename>task</filename> class.
    </para>
</section>

<section id='ref-classes-packageinfo'>
    <title><filename>packageinfo.bbclass</filename></title>

    <para>
        The <filename>packageinfo</filename> class
        gives a BitBake user interface the ability to retrieve information
        about output packages from the <filename>pkgdata</filename> files.
    </para>

    <para>
        This class is enabled automatically when using the
        <ulink url='&YOCTO_HOME_URL;/tools-resources/projects/hob'>Hob</ulink>
        user interface.
    </para>
</section>

<section id='ref-classes-patch'>
    <title><filename>patch.bbclass</filename></title>

    <para>
        The <filename>patch</filename> class provides all functionality for
        applying patches during the <filename>do_patch</filename> task.
    </para>

    <para>
        This class is enabled by default because it is inherited by the
        <link linkend='ref-classes-base'><filename>base</filename></link>
        class.
    </para>
</section>

<section id='ref-classes-perlnative'>
    <title><filename>perlnative.bbclass</filename></title>

    <para>
        When inherited by a recipe, the <filename>perlnative</filename> class
        supports using the native version of Perl built by the build system
        rather than using the version provided by the build host.
    </para>
</section>

<section id='ref-classes-pixbufcache'>
    <title><filename>pixbufcache.bbclass</filename></title>

    <para>
        The <filename>pixbufcache</filename> class generates the proper
        post-install and post-remove (postinst/postrm) scriptlets for packages
        that install pixbuf loaders, which are used with
        <filename>gdk-pixbuf</filename>.
        These scriptlets call <filename>update_pixbuf_cache</filename>
        to add the input method modules to the cache.
        Since the cache files are architecture-specific,
        <filename>update_pixbuf_cache</filename> is run using QEMU if the
        postinst scriptlets need to be run on the build host during image
        creation.
    </para>

    <para>
        If the pixbuf loaders modules being installed are in packages other
        than the main package, set
        <link linkend='var-PIXBUF_PACKAGES'><filename>PIXBUF_PACKAGES</filename></link>
        to include the packages containing the modules.
    </para>
</section>

<section id='ref-classes-pkgconfig'>
    <title><filename>pkgconfig.bbclass</filename></title>

    <para>
        The <filename>pkg-config</filename> class provides a standard way to get
        header and library information.
        This class aims to smooth integration of
        <filename>pkg-config</filename> into libraries that use it.
    </para>

    <para>
        During staging, BitBake installs <filename>pkg-config</filename> data into the
        <filename>sysroots/</filename> directory.
        By making use of sysroot functionality within <filename>pkg-config</filename>,
        this class no longer has to manipulate the files.
    </para>
</section>

<section id='ref-classes-populate-sdk'>
    <title><filename>populate_sdk.bbclass</filename></title>

    <para>
        The <filename>populate_sdk</filename> class facilitates compatibility
        with SDK-only recipes.
    </para>
</section>

<section id='ref-classes-populate-sdk-*'>
    <title><filename>populate_sdk_*.bbclass</filename></title>

    <para>
        The <filename>populate_sdk_*</filename> classes support SDK creation
        and consist of the following classes:
        <itemizedlist>
            <listitem><para><emphasis><filename>populate_sdk_base</filename>:</emphasis>
                The base class supporting SDK creation under all package
                managers (i.e. DEB, RPM, and IPK).</para></listitem>
            <listitem><para><emphasis><filename>populate_sdk_deb</filename>:</emphasis>
                Supports creation of the SDK given the Debian package manager.
                </para></listitem>
            <listitem><para><emphasis><filename>populate_sdk_rpm</filename>:</emphasis>
                Supports creation of the SDK given the RPM package manager.
                </para></listitem>
            <listitem><para><emphasis><filename>populate_sdk_ipk</filename>:</emphasis>
                Supports creation of the SDK given the IPK package manager.
                </para></listitem>
        </itemizedlist>
    </para>

    <para>
        The <filename>populate_sdk_base</filename> package inherits the
        appropriate <filename>populate_sdk_*</filename> (i.e.
        <filename>deb</filename>, <filename>rpm</filename>, and
        <filename>ipk</filename>) based on
        <link linkend='var-IMAGE_PKGTYPE'><filename>IMAGE_PKGTYPE</filename></link>.
    </para>

    <para>
        The base class ensures all source and destination directories are
        established and then populates the SDK.
        After populating the SDK, the <filename>populate_sdk_base</filename>
        class constructs two images:
        <link linkend='var-SDK_ARCH'><filename>SDK_ARCH</filename></link><filename>-nativesdk</filename>,
        which contains the cross-compiler and associated tooling, and the
        target, which contains a target root filesystem that is configured for
        the SDK usage.
        These two images reside in
        <link linkend='var-SDK_OUTPUT'><filename>SDK_OUTPUT</filename></link>,
        which consists of the following:
        <literallayout class='monospaced'>
     ${SDK_OUTPUT}/&lt;sdk_arch-nativesdk pkgs&gt;
     ${SDK_OUTPUT}/${SDKTARGETSYSROOT}/&lt;target pkgs&gt;
        </literallayout>
    </para>

    <para>
        Finally, the base populate SDK class creates the toolchain
        environment setup script, the tarball of the SDK, and the installer.
    </para>

    <para>
        The respective <filename>populate_sdk_deb</filename>,
        <filename>populate_sdk_rpm</filename>, and
        <filename>populate_sdk_ipk</filename> classes each support the
        specific type of SDK.
        These classes are inherited by and used with the
        <filename>populate_sdk_base</filename> class.
    </para>
</section>

<section id='ref-classes-prexport'>
    <title><filename>prexport.bbclass</filename></title>

    <para>
        The <filename>prexport</filename> class provides functionality for
        exporting
        <link linkend='var-PR'><filename>PR</filename></link> values.
        <note>
            This class is not intended to be used directly.
            Rather, it is enabled when using
            "<filename>bitbake-prserv-tool export</filename>".
        </note>
    </para>
</section>

<section id='ref-classes-primport'>
    <title><filename>primport.bbclass</filename></title>

    <para>
        The <filename>primport</filename> class provides functionality for
        importing
        <link linkend='var-PR'><filename>PR</filename></link> values.
        <note>
            This class is not intended to be used directly.
            Rather, it is enabled when using
            "<filename>bitbake-prserv-tool import</filename>".
        </note>
    </para>
</section>

<section id='ref-classes-prserv'>
    <title><filename>prserv.bbclass</filename></title>

    <para>
        The <filename>prserv</filename> class provides functionality for
        using a
        <ulink url='&YOCTO_DOCS_DEV_URL;#working-with-a-pr-service'>PR service</ulink>
        in order to automatically manage the incrementing of the
        <link linkend='var-PR'><filename>PR</filename></link> variable for
        each recipe.
    </para>

    <para>
        This class is enabled by default because it is inherited by the
        <link linkend='ref-classes-package'><filename>package</filename></link>
        class.
        However, the OpenEmbedded build system will not use this variable
        unless
        <link linkend='var-PRSERV_HOST'><filename>PRSERV_HOST</filename></link>
        has been set.
    </para>
</section>

<section id='ref-classes-ptest'>
    <title><filename>ptest.bbclass</filename></title>

    <para>
        The <filename>ptest</filename> class provides functionality for
        packaging and installing runtime tests for recipes that build software
        that provides these tests.
    </para>

    <para>
        This class is intended to be inherited by individual recipes.
        However, the class' functionality is largely disabled unless "ptest"
        appears in
        <link linkend='var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></link>.
        See the
        "<ulink url='&YOCTO_DOCS_DEV_URL;#testing-packages-with-ptest'>Testing Packages With ptest</ulink>"
        section in the Yocto Project Development Manual for more information
        on ptest.
    </para>
</section>

<section id='ref-classes-python-dir'>
    <title><filename>python-dir.bbclass</filename></title>

    <para>
        The <filename>python-dir</filename> class provides the base version,
        location, and site package location for Python.
    </para>
</section>

<section id='ref-classes-pythonnative'>
    <title><filename>pythonnative.bbclass</filename></title>

    <para>
        The <filename>pythonnative</filename> causes the OpenEmbedded build
        system to use the native version of Python, which is built by the
        build system.
        Normally, the OpenEmbedded build system uses the version of Python
        that is built by the build host.
        <note>
            This class must be inherited by a recipe in order to be used.
        </note>
    </para>
</section>

<section id='ref-classes-qemu'>
    <title><filename>qemu.bbclass</filename></title>

    <para>
        The <filename>qemu</filename> class provides functionality for recipes
        that either need QEMU or test for the existence of QEMU.
        Typically, this class is used to run programs for a target system on
        the build host using QEMU's application emulation mode.
    </para>
</section>

<section id='ref-classes-qmake*'>
    <title><filename>qmake*.bbclass</filename></title>

    <para>
        The <filename>qmake*</filename> classes support recipes that
        need to build software that uses Qt's <filename>qmake</filename>
        build system and are comprised of the following:
        <itemizedlist>
            <listitem><para><emphasis><filename>qmake_base</filename>:</emphasis>
                Provides base functionality for all versions of
                <filename>qmake</filename>.</para></listitem>
            <listitem><para><emphasis><filename>qmake2</filename>:</emphasis>
                Extends base functionality for <filename>qmake</filename> 2.x as
                used by Qt 4.x.</para></listitem>
        </itemizedlist>
    </para>

    <para>
        If you need to set any configuration variables or pass any options to
        <filename>qmake</filename>, you can add these to the
        <link linkend='var-EXTRA_QMAKEVARS_PRE'><filename>EXTRA_QMAKEVARS_PRE</filename></link>
        or
        <link linkend='var-EXTRA_QMAKEVARS_POST'><filename>EXTRA_QMAKEVARS_POST</filename></link>
        variables, depending on whether the arguments need to be before or
        after the <filename>.pro</filename> file list on the command line,
        respectively.
    </para>

    <para>
        By default, all <filename>.pro</filename> files are built.
        If you want to specify your own subset of <filename>.pro</filename>
        files to be built, specify them in the
        <link linkend='var-QMAKE_PROFILES'><filename>QMAKE_PROFILES</filename></link>
        variable.
    </para>
</section>

<section id='ref-classes-qt4*'>
    <title><filename>qt4*.bbclass</filename></title>

    <para>
        The <filename>qt4*</filename> classes support recipes that need to
        build software that uses the Qt development framework version 4.x
        and consist of the following:
        <itemizedlist>
            <listitem><para><emphasis><filename>qt4e</filename>:</emphasis>
                Supports building against Qt/Embedded, which uses the
                framebuffer for graphical output.</para></listitem>
            <listitem><para><emphasis><filename>qt4x11</filename>:</emphasis>
                Supports building against Qt/X11.</para></listitem>
        </itemizedlist>
    </para>

    <para>
        The classes inherit the
        <link linkend='ref-classes-qmake*'><filename>qmake2</filename></link>
        class.
    </para>
</section>

<section id='ref-classes-relocatable'>
    <title><filename>relocatable.bbclass</filename></title>

    <para>
        The <filename>relocatable</filename> class enables relocation of
        binaries when they are installed into the sysroot.
    </para>

    <para>
        This class makes use of the
        <link linkend='ref-classes-chrpath'><filename>chrpath</filename></link>
        class and is used by both the
        <link linkend='ref-classes-cross'><filename>cross</filename></link>
        and
        <link linkend='ref-classes-native'><filename>native</filename></link>
        classes.
    </para>
</section>

<section id='ref-classes-rm-work'>
    <title><filename>rm_work.bbclass</filename></title>

    <para>
        The <filename>rm_work</filename> class supports deletion of temporary
        workspace, which can ease your hard drive demands during builds.
    </para>

    <para>
        The OpenEmbedded build system can use a substantial amount of disk
        space during the build process.
        A portion of this space is the work files under the
        <filename>${TMPDIR}/work</filename> directory for each recipe.
        Once the build system generates the packages for a recipe, the work
        files for that recipe are no longer needed.
        However, by default, the build system preserves these files
        for inspection and possible debugging purposes.
        If you would rather have these files deleted to save disk space
        as the build progresses, you can enable <filename>rm_work</filename>
        by adding the following to your <filename>local.conf</filename> file,
        which is found in the
        <ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>.
        <literallayout class='monospaced'>
    INHERIT += "rm_work"
        </literallayout>
        If you are modifying and building source code out of the work directory
        for a recipe, enabling <filename>rm_work</filename> will potentially
        result in your changes to the source being lost.
        To exclude some recipes from having their work directories deleted by
        <filename>rm_work</filename>, you can add the names of the recipe or
        recipes you are working on to the <filename>RM_WORK_EXCLUDE</filename>
        variable, which can also be set in your <filename>local.conf</filename>
        file.
        Here is an example:
        <literallayout class='monospaced'>
    RM_WORK_EXCLUDE += "busybox eglibc"
        </literallayout>
    </para>
</section>

<section id='ref-classes-rootfs*'>
    <title><filename>rootfs*.bbclass</filename></title>

    <para>
        The <filename>rootfs*</filename> classes add support for creating
        images in several formats and consist of the following:
        <itemizedlist>
            <listitem><para>The
                <filename><link linkend='var-IMAGE_FSTYPES'>IMAGE_FSTYPES</link></filename>
                variable controls the types of images to generate.
                </para></listitem>
            <listitem><para>The
                <filename><link linkend='var-IMAGE_INSTALL'>IMAGE_INSTALL</link></filename>
                variable controls the list of packages to install into the
                image.</para></listitem>
        </itemizedlist>
        First, the root filesystem is created from packages using
        one of the <filename>rootfs_*.bbclass</filename>
        files (depending on the package format used) and then the image
        is created.
    </para>
</section>

<section id='ref-classes-sanity'>
    <title><filename>sanity.bbclass</filename></title>

    <para>
        The <filename>sanity</filename> class checks to see if prerequisite
        software is present on the host system so that users can be notified
        of potential problems that might affect their build.
        The class also performs basic user configuration checks from
        the <filename>local.conf</filename> configuration file to
        prevent common mistakes that cause build failures.
        Distribution policy usually determines whether to include this class.
    </para>
</section>

<section id='ref-classes-scons'>
    <title><filename>scons.bbclass</filename></title>

    <para>
        The <filename>scons</filename> class supports recipes that need to
        build software that uses the SCons build system.
        You can use the
        <link linkend='var-EXTRA_OESCONS'><filename>EXTRA_OESCONS</filename></link>
        variable to specify additional configuration options you want to pass
        SCons command line.
    </para>
</section>

<section id='ref-classes-sdl'>
    <title><filename>sdl.bbclass</filename></title>

    <para>
        The <filename>sdl</filename> class supports recipes that need to build
        software that uses the Simple DirectMedia Layer (SDL) library.
    </para>
</section>

<section id='ref-classes-setuptools'>
    <title><filename>setuptools.bbclass</filename></title>

    <para>
        The <filename>setuptools</filename> class supports extensions that use
        setuptools-based build systems.
        If your recipe uses these build systems, the recipe needs to
        inherit the <filename>setuptools</filename> class.
    </para>
</section>

<section id='ref-classes-sip'>
    <title><filename>sip.bbclass</filename></title>

    <para>
        The <filename>sip</filename> class
        supports recipes that build or package SIP-based Python bindings.
    </para>
</section>

<section id='ref-classes-siteconfig'>
    <title><filename>siteconfig.bbclass</filename></title>

    <para>
        The <filename>siteconfig</filename> class
        provides functionality for handling site configuration.
        The class is used by the
        <link linkend='ref-classes-autotools'><filename>autotools</filename></link>
        class to accelerate the <filename>do_configure</filename> task.
    </para>
</section>

<section id='ref-classes-siteinfo'>
    <title><filename>siteinfo.bbclass</filename></title>

    <para>
        The <filename>siteinfo</filename> class provides information about
        the targets that might be needed by other classes or recipes.
    </para>

    <para>
        As an example, consider Autotools, which can require tests that must
        execute on the target hardware.
        Since this is not possible in general when cross compiling, site
        information is used to provide cached test results so these tests can
        be skipped over but still make the correct values available.
        The
        <filename><link linkend='structure-meta-site'>meta/site directory</link></filename>
        contains test results sorted into different categories such as
        architecture, endianness, and the <filename>libc</filename> used.
        Site information provides a list of files containing data relevant to
        the current build in the
        <filename><link linkend='var-CONFIG_SITE'>CONFIG_SITE</link></filename> variable
        that Autotools automatically picks up.
    </para>

    <para>
        The class also provides variables like
        <filename><link linkend='var-SITEINFO_ENDIANNESS'>SITEINFO_ENDIANNESS</link></filename>
        and <filename><link linkend='var-SITEINFO_BITS'>SITEINFO_BITS</link></filename>
        that can be used elsewhere in the metadata.
    </para>

    <para>
        Because the
        <link linkend='ref-classes-base'><filename>base</filename></link> class
        includes the <filename>siteinfo</filename> class, it is always active.
    </para>
</section>

<section id='ref-classes-spdx'>
    <title><filename>spdx.bbclass</filename></title>

    <para>
        The <filename>spdx</filename> class integrates real-time license
        scanning, generation of SPDX standard output, and verification
        of license information during the build.
        <note>
            This class is currently at the prototype stage in the 1.5
            release.
        </note>
    </para>
</section>

<section id='ref-classes-sstate'>
    <title><filename>sstate.bbclass</filename></title>

    <para>
        The <filename>sstate</filename> class provides support for Shared
        State (sstate).
        By default, the class is enabled through the
        <link linkend='var-INHERIT_DISTRO'><filename>INHERIT_DISTRO</filename></link>
        variable's default value.
    </para>

    <para>
        For more information on sstate, see the
        "<link linkend='shared-state-cache'>Shared State Cache</link>"
        section.
    </para>
</section>

<section id='ref-classes-staging'>
    <title><filename>staging.bbclass</filename></title>

    <para>
        The <filename>staging</filename> class provides support for staging
        files into the sysroot during the
        <filename>do_populate_sysroot</filename> task.
        The class is enabled by default because it is inherited by the
        <link linkend='ref-classes-base'><filename>base</filename></link>
        class.
    </para>
</section>

<section id='ref-classes-syslinux'>
    <title><filename>syslinux.bbclass</filename></title>

    <para>
        The <filename>syslinux</filename> class provides syslinux-specific
        functions for building bootable images.
    </para>

    <para>
        The class supports the following variables:
        <itemizedlist>
            <listitem><para><emphasis><link linkend='var-INITRD'><filename>INITRD</filename></link>:</emphasis>
                Indicates a filesystem image to use as an initial RAM disk
                (initrd).
                This variable is optional.</para></listitem>
            <listitem><para><emphasis><link linkend='var-ROOTFS'><filename>ROOTFS</filename></link>:</emphasis>
                Indicates a filesystem image to include as the root filesystem.
                This variable is optional.</para></listitem>
            <listitem><para><emphasis><link linkend='var-AUTO_SYSLINUXMENU'><filename>AUTO_SYSLINUXMENU</filename></link>:</emphasis>
                Enables creating an automatic menu when set to "1".
                </para></listitem>
            <listitem><para><emphasis><link linkend='var-LABELS'><filename>LABELS</filename></link>:</emphasis>
                Lists targets for automatic configuration.
                </para></listitem>
            <listitem><para><emphasis><link linkend='var-APPEND'><filename>APPEND</filename></link>:</emphasis>
                Lists append string overrides for each label.
                </para></listitem>
            <listitem><para><emphasis><link linkend='var-SYSLINUX_OPTS'><filename>SYSLINUX_OPTS</filename></link>:</emphasis>
                Lists additional options to add to the syslinux file.
                Semicolon characters separate multiple options.
                </para></listitem>
            <listitem><para><emphasis><link linkend='var-SYSLINUX_SPLASH'><filename>SYSLINUX_SPLASH</filename></link>:</emphasis>
                Lists a background for the VGA boot menu when you are using the
                boot menu.</para></listitem>
            <listitem><para><emphasis><link linkend='var-SYSLINUX_DEFAULT_CONSOLE'><filename>SYSLINUX_DEFAULT_CONSOLE</filename></link>:</emphasis>
                Set to "console=ttyX" to change kernel boot default console.
                </para></listitem>
            <listitem><para><emphasis><link linkend='var-SYSLINUX_SERIAL'><filename>SYSLINUX_SERIAL</filename></link>:</emphasis>
                Sets an alternate serial port.
                Or, turns off serial when the variable is set with an
                empty string.</para></listitem>
            <listitem><para><emphasis><link linkend='var-SYSLINUX_SERIAL_TTY'><filename>SYSLINUX_SERIAL_TTY</filename></link>:</emphasis>
                Sets an alternate "console=tty..." kernel boot argument.
                </para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='ref-classes-systemd'>
    <title><filename>systemd.bbclass</filename></title>

    <para>
        The <filename>systemd</filename> class provides support for recipes
        that install <filename>systemd</filename> unit files.
    </para>

    <para>
        The functionality for this class is disabled unless you have "systemd"
        in
        <link linkend='var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></link>.
    </para>

    <para>
        Under this class, unit files are installed into
        <filename>${</filename><link linkend='var-D'><filename>D</filename></link><filename>}${systemd_unitdir}/system</filename>
        during the <filename>do_install</filename> task.
        If the unit files being installed go into packages other than the
        main package, you need to set
        <link linkend='var-SYSTEMD_PACKAGES'><filename>SYSTEMD_PACKAGES</filename></link>
        in your recipe to identify the packages in which the files will be
        installed.
    </para>

    <para>
        You should set
        <link linkend='var-SYSTEMD_SERVICE'><filename>SYSTEMD_SERVICE</filename></link>
        to the name of the service file.
        You should also use a package name override to indicate the package
        to which the value applies.
        If the value applies to the recipe's main package, use
        <filename>${</filename><link linkend='var-PN'><filename>PN</filename></link><filename>}</filename>.
        Here is an example from the connman recipe:
        <literallayout class='monospaced'>
     SYSTEMD_SERVICE_${PN} = "connman.service"
        </literallayout>
        Services are set up to start on boot automatically unless
        you have set
        <link linkend='var-SYSTEMD_AUTO_ENABLE'><filename>SYSTEMD_AUTO_ENABLE</filename></link>
        to "disable".
    </para>

    <para>
        For more information on <filename>systemd</filename>, see the
        "<ulink url='&YOCTO_DOCS_DEV_URL;#selecting-an-initialization-manager'>Selecting an Initialization Manager</ulink>"
        section in the Yocto Project Development Manual.
    </para>
</section>

<section id='ref-classes-terminal'>
    <title><filename>terminal.bbclass</filename></title>

    <para>
        The <filename>terminal</filename> class provides support for starting
        a terminal session.
        The
        <link linkend='var-OE_TERMINAL'><filename>OE_TERMINAL</filename></link>
        variable controls which terminal emulator is used for the session.
    </para>

    <para>
        You can use this class anywhere a separate terminal session needs to
        be started.
        To use the class, include the
        <link linkend='ref-classes-patch'><filename>patch</filename></link>
        class if
        <link linkend='var-PATCHRESOLVE'><filename>PATCHRESOLVE</filename></link>
        is set to "user", include the
        <link linkend='ref-classes-cml1'><filename>cml1</filename></link>
        class, and include the
        <link linkend='ref-classes-devshell'><filename>devshell</filename></link>
        class.
    </para>
</section>

<section id='ref-classes-testimage'>
    <title><filename>testimage.bbclass</filename></title>

    <para>
        The <filename>testimage</filename> class supports running automated
        tests against images.
        The class handles loading the tests and starting the image.
        <note>
            Currently, there is only support for running these tests
            under QEMU.
        </note>
    </para>

    <para>
        To use the class, you need to perform steps to set up the
        environment.
        The tests are commands that run on the target system over
        <filename>ssh</filename>.
        they are written in Python and make use of the
        <filename>unittest</filename> module.
    </para>

    <para>
        For information on how to enable, run, and create new tests, see the
        "<ulink url='&YOCTO_DOCS_DEV_URL;#performing-automated-runtime-testing'>Performing Automated Runtime Testing</ulink>"
        section.
    </para>
</section>

<section id='ref-classes-tinderclient'>
    <title><filename>tinderclient.bbclass</filename></title>

    <para>
        The <filename>tinderclient</filename> class submits build results to
        an external Tinderbox instance.
        <note>
            This class is currently unmaintained.
        </note>
    </para>
</section>

<section id='ref-classes-toaster'>
    <title><filename>toaster.bbclass</filename></title>

    <para>
        The <filename>toaster</filename> class collects information about
        packages and images and sends them as events that the BitBake
        user interface can receive.
        The class is enabled when the Toaster user interface is running.
    </para>

    <para>
        This class is not intended to be used directly.
    </para>
</section>

<section id='ref-classes-toolchain-scripts'>
    <title><filename>toolchain-scripts.bbclass</filename></title>

    <para>
        The <filename>toolchain-scripts</filename> class provides the scripts
        used for setting up the environment for installed SDKs.
    </para>
</section>

<section id='ref-classes-typecheck'>
    <title><filename>typecheck.bbclass</filename></title>

    <para>
        The <filename>typecheck</filename> class provides support for
        validating the values of variables set at the configuration level
        against their defined types.
        The OpenEmbedded build system allows you to define the type of a
        variable using the "type" varflag.
        Here is an example:
        <literallayout class='monospaced'>
     IMAGE_FEATURES[type] = "list"
        </literallayout>
    </para>
</section>

<section id='ref-classes-uboot-config'>
    <title><filename>uboot-config.bbclass</filename></title>

    <para>
        The <filename>uboot-config</filename> class provides support for
        U-Boot configuration for a machine.
        Specify the machine in your recipe as follows:
        <literallayout class='monospaced'>
     UBOOT_CONFIG ??= &lt;default&gt;
     UBOOT_CONFIG[foo] = "config,images"
        </literallayout>
        You can also specify the machine using this method:
        <literallayout class='monospaced'>
     UBOOT_MACHINE = "config"
        </literallayout>
        See the
        <link linkend='var-UBOOT_CONFIG'><filename>UBOOT_CONFIG</filename></link>
        and
        <link linkend='var-UBOOT_MACHINE'><filename>UBOOT_MACHINE</filename></link>
        variables for additional information.
    </para>
</section>

<section id='ref-classes-update-alternatives'>
    <title><filename>update-alternatives.bbclass</filename></title>

    <para>
        The <filename>update-alternatives</filename> class helps the
        alternatives system when multiple sources provide the same command.
        This situation occurs when several programs that have the same or
        similar function are installed with the same name.
        For example, the <filename>ar</filename> command is available from the
        <filename>busybox</filename>, <filename>binutils</filename> and
        <filename>elfutils</filename> packages.
        The <filename>update-alternatives</filename> class handles
        renaming the binaries so that multiple packages can be installed
        without conflicts.
        The <filename>ar</filename> command still works regardless of which
        packages are installed or subsequently removed.
        The class renames the conflicting binary in each package and symlinks
        the highest priority binary during installation or removal of packages.
    </para>

    <para>
        To use this class, you need to define a number of variables:
        <itemizedlist>
            <listitem><para><link linkend='var-ALTERNATIVE'><filename>ALTERNATIVE</filename></link>
                </para></listitem>
            <listitem><para><link linkend='var-ALTERNATIVE_LINK_NAME'><filename>ALTERNATIVE_LINK_NAME</filename></link>
                </para></listitem>
            <listitem><para><link linkend='var-ALTERNATIVE_TARGET'><filename>ALTERNATIVE_TARGET</filename></link>
                </para></listitem>
            <listitem><para><link linkend='var-ALTERNATIVE_PRIORITY'><filename>ALTERNATIVE_PRIORITY</filename></link>
                </para></listitem>
        </itemizedlist>
        These variables list alternative commands needed by a package,
        provide pathnames for links, default links for targets, and
        so forth.
        For details on how to use this class, see the comments in the
        <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/poky/tree/meta/classes/update-alternatives.bbclass'><filename>update-alternatives.bbclass</filename></ulink>.
    </para>

    <note>
        You can use the <filename>update-alternatives</filename> command
        directly in your recipes.
        However, this class simplifies things in most cases.
    </note>
</section>

<section id='ref-classes-update-rc.d'>
    <title><filename>update-rc.d.bbclass</filename></title>

    <para>
        The <filename>update-rc.d</filename> class uses
        <filename>update-rc.d</filename> to safely install an
        initialization script on behalf of the package.
        The OpenEmbedded build system takes care of details such as making
        sure the script is stopped before a package is removed and started when
        the package is installed.
    </para>

    <para>
        Three variables control this class:
        <filename><link linkend='var-INITSCRIPT_PACKAGES'>INITSCRIPT_PACKAGES</link></filename>,
        <filename><link linkend='var-INITSCRIPT_NAME'>INITSCRIPT_NAME</link></filename> and
        <filename><link linkend='var-INITSCRIPT_PARAMS'>INITSCRIPT_PARAMS</link></filename>.
        See the variable links for details.
    </para>
</section>

<section id='ref-classes-useradd'>
    <title><filename>useradd.bbclass</filename></title>

    <para>
        The <filename>useradd</filename> class supports recipes that restrict
        packages to certain users or groups.
        For example, if you have packages that install files that are owned
        by custom users or groups, you can use this class to specify
        those packages and then associate them with the users and groups.
        The <filename>meta-skeleton/recipes-skeleton/useradd/useradd-example.bb</filename>
        recipe in the <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>
        provides a simple example that shows how to add three
        users and groups to two packages.
        See the <filename>useradd-example.bb</filename> recipe for more
        information on how to use this class.
    </para>
</section>

<section id='ref-classes-utility-tasks'>
    <title><filename>utility-tasks.bbclass</filename></title>

    <para>
        The <filename>utility-tasks</filename> class provides support for
        various "utility" type tasks that are applicable to all recipes,
        such as <filename>do_clean</filename> and
        <filename>do_listtasks</filename>.
    </para>

    <para>
        This class is enabled by default because it is inherited by
        the
        <link linkend='ref-classes-base'><filename>base</filename></link>
        class.
    </para>
</section>

<section id='ref-classes-utils'>
    <title><filename>utils.bbclass</filename></title>

    <para>
        The <filename>utils</filename> class provides some useful Python
        functions that are typically used in inline Python expressions
        (e.g. <filename>${@...}</filename>).
        One example use is for <filename>base_contains()</filename>.
    </para>

    <para>
        This class is enabled by default because it is inherited by the
        <link linkend='ref-classes-base'><filename>base</filename></link>
        class.
    </para>
</section>

<section id='ref-classes-vala'>
    <title><filename>vala.bbclass</filename></title>

    <para>
        The <filename>vala</filename> class supports recipes that need to
        build software written using the Vala programming language.
    </para>
</section>

<section id='ref-classes-waf'>
    <title><filename>waf.bbclass</filename></title>

    <para>
        The <filename>waf</filename> class supports recipes that need to build
        software that uses the Waf build system.
        You can use the
        <link linkend='var-EXTRA_OECONF'><filename>EXTRA_OECONF</filename></link>
        variable to specify additional configuration options to be passed on
        the Waf command line.
    </para>
</section>

<section id='ref-classes-externalsrc'>
    <title><filename>externalsrc.bbclass</filename></title>

    <para>
        The <filename>externalsrc</filename> class supports building software
        from source code that is external to the OpenEmbedded build system.
        Building software from an external source tree means that the build
        system's normal fetch, unpack, and patch process is not used.
    </para>

    <para>
        By default, the OpenEmbedded build system uses the
        <link linkend='var-S'><filename>S</filename></link> and
        <link linkend='var-B'><filename>B</filename></link> variables to
        locate unpacked recipe source code and to build it, respectively.
        When your recipe inherits the <filename>externalsrc</filename> class,
        you use the
        <link linkend='var-EXTERNALSRC'><filename>EXTERNALSRC</filename></link>
        and
        <link linkend='var-EXTERNALSRC_BUILD'><filename>EXTERNALSRC_BUILD</filename></link>
        variables to ultimately define <filename>S</filename> and
        <filename>B</filename>.
    </para>

    <para>
        By default, this class expects the source code to support recipe builds
        that use the <link linkend='var-B'><filename>B</filename></link>
        variable to point to the directory in which the OpenEmbedded build
        system places the generated objects built from the recipes.
        By default, the <filename>B</filename> directory is set to the
        following, which is separate from the source directory
        (<filename>S</filename>):
        <literallayout class='monospaced'>
     ${WORKDIR}/${BPN}/{PV}/
        </literallayout>
        See these variables for more information:
        <link linkend='var-WORKDIR'><filename>WORKDIR</filename></link>,
        <link linkend='var-BPN'><filename>BPN</filename></link>, and
        <link linkend='var-PV'><filename>PV</filename></link>,
    </para>

    <para>
        For more information on the
        <filename>externalsrc</filename> class, see the comments in
        <filename>meta/classes/externalsrc.bbclass</filename> in the
        <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>.
        For information on how to use the <filename>externalsrc</filename>
        class, see the
        "<ulink url='&YOCTO_DOCS_DEV_URL;#building-software-from-an-external-source'>Building Software from an External Source</ulink>"
        section in the Yocto Project Development Manual.
    </para>
</section>

<section id='ref-classes-others'>
    <title>Other Classes</title>

    <para>
        Thus far, this chapter has discussed only the most useful and important
        classes.
        However, other classes exist within the <filename>meta/classes</filename> directory
        in the <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>.
        You can examine the <filename>.bbclass</filename> files directly for more
        information.
    </para>
</section>

<!-- Undocumented classes are:
        allarch.bbclass
        bin_package.bbclass
        blacklist.bbclass
        bootimg.bbclass
        boot-directdisk.bbclass
        bugzilla.bbclass
        buildhistory.bbclass
        buildstats.bbclass
        ccache.bbclass
        chrpath.bbclass
        clutter.bbclass
        cmake.bbclass
        cml1.bbclass
        copyleft_compliance.bbclass
        core-image.bbclass
        cross.bbclass
        cross-canadian.bbclass
        crosssdk.bbclass
        deploy.bbclass
        distrodata.bbclass
        distro_features_check.bbclass
        dummy.bbclass
        extrausers.bbclass
        fontcache.bbclass
        gconf.bbclass
        gettext.bbclass
        gnomebase.bbclass
        gnome.bbclass
        grub-efi.bbclass
        gsettings.bbclass
        gtk-doc.bbclass
        gtk-icon-cache.bbclass
        gtk-immodules-cache.bbclass
        gzipnative.bbclass
        icecc.bbclass
        image-empty.bbclass
        image-live.bbclass
        image-vmdk.bbclass
        image-mklibs.bbclass
        image-prelink.bbclass
        image-swab.bbclass
        image_types.bbclass
        image_types_uboot.bbclass
        insserv.bbclass
        kernel-arch.bbclass
        kernel-module-split.bbclass
        kernel-yocto.bbclass
        lib_package.bbclass
        linux-kernel-base.bbclass
        license.bbclass
        logging.bbclass
        meta.bbclass
        metadata_scm.bbclass
        migrate_localcount.bbclass
        mime.bbclass
        mirrors.bbclass
        multilib*.bbclass
        native.bbclass
        nativesdk.bbclass
        oelint.bbclass
        own-mirrors.bbclass
        packagedata.bbclass
        packageinfo.bbclass
        patch.bbclass
        perlnative.bbclass
        pixbufcache.bbclass
        pkg_distribute.bbclass
        pkg_metainfo.bbclass
        populate_sdk*.bbclass
        prexport.bbclass
        primport.bbclass
        prserv.bbclass
        ptest.bbclass
        python-dir.bbclass
        pythonnative.bbclass
        qemu.bbclass
        qmake*.bbclass
        qt4*.bbclass
        recipe_sanity.bbclass
        relocatable.bbclass
        scons.bbclass
        sdl.bbclass
        setuptools.bbclass
        sip.bbclass
        siteconfig.bbclass
        sourcepkg.bbclass
        spdx.bbclass
        sstate.bbclass
        staging.bbclass
        syslinux.bbclass
        systemd.bbclass
        terminal.bbclass
        tinderclient.bbclass
        toolchain-scripts.bbclass
        typecheck.bbclass
        uboot-config.bbclass
        utility-tasks.bbclass
        utils.bbclass
        vala.bbclass
        waf.bbclass
-->


</chapter>
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