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<chapter id='ref-manual-intro'>
<title>Introduction</title>

<section id='intro-welcome'>
    <title>Introduction</title>

    <para>
        This manual provides reference information for the current release of the Yocto Project.
        The Yocto Project is an open-source collaboration project focused on embedded Linux
        developers.
        Amongst other things, the Yocto Project uses the OpenEmbedded build system, which
        is based on the Poky project, to construct complete Linux images.
        You can find complete introductory and getting started information on the Yocto Project
        by reading the
        <ulink url='&YOCTO_DOCS_QS_URL;'>Yocto Project Quick Start</ulink>.
        For task-based information using the Yocto Project, see the
        <ulink url='&YOCTO_DOCS_DEV_URL;'>Yocto Project Development Manual</ulink>
        and the <ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;'>Yocto Project Linux Kernel Development Manual</ulink>.
        For Board Support Package (BSP) structure information, see the
        <ulink url='&YOCTO_DOCS_BSP_URL;'>Yocto Project Board Support Package (BSP) Developer's Guide</ulink>.
        You can find information on tracing and profiling in the
        <ulink url='&YOCTO_DOCS_PROF_URL;'>Yocto Project Profiling and Tracing Manual</ulink>.
        For information on BitBake, which is the task execution tool the
        OpenEmbedded build system is based on, see the
        <ulink url='&YOCTO_DOCS_BB_URL;#bitbake-user-manual'>BitBake User Manual</ulink>.
        Finally, you can also find lots of Yocto Project information on the
        <ulink url="&YOCTO_HOME_URL;">Yocto Project website</ulink>.
    </para>
</section>

<section id='intro-manualoverview'>
    <title>Documentation Overview</title>
    <para>
        This reference manual consists of the following:
        <itemizedlist>
            <listitem><para><emphasis>
                <link linkend='usingpoky'>Using the Yocto Project</link>:</emphasis>
                Provides an overview of the components that make up the Yocto Project
                followed by information about debugging images created in the Yocto Project.
                </para></listitem>
            <listitem><para><emphasis>
                <link linkend='closer-look'>A Closer Look at the Yocto Project Development Environment</link>:</emphasis>
                Provides a more detailed look at the Yocto Project development
                environment within the context of development.
                </para></listitem>
            <listitem><para><emphasis>
                <link linkend='technical-details'>Technical Details</link>:</emphasis>
                Describes fundamental Yocto Project components as well as an explanation
                behind how the Yocto Project uses shared state (sstate) cache to speed build time.
                </para></listitem>
            <listitem><para><emphasis>
                <link linkend='migration'>Migrating to a Newer Yocto Project Release</link>:</emphasis>
                Describes release-specific information that helps you move from
                one Yocto Project Release to another.
                </para></listitem>
            <listitem><para><emphasis>
                <link linkend='ref-structure'>Directory Structure</link>:</emphasis>
                Describes the
                <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink> created
                either by unpacking a released Yocto Project tarball on your host development system,
                or by cloning the upstream
                <ulink url='&YOCTO_DOCS_DEV_URL;#poky'>Poky</ulink> Git repository.
                </para></listitem>
            <listitem><para><emphasis>
                <link linkend='ref-classes'>Classes</link>:</emphasis>
                Describes the classes used in the Yocto Project.</para></listitem>
            <listitem><para><emphasis>
                <link linkend='ref-tasks'>Tasks</link>:</emphasis>
                Describes the tasks defined by the OpenEmbedded build system.
                </para></listitem>
            <listitem><para><emphasis>
                <link linkend='ref-qa-checks'>QA Error and Warning Messages</link>:</emphasis>
                Lists and describes QA warning and error messages.
                </para></listitem>
            <listitem><para><emphasis>
                <link linkend='ref-images'>Images</link>:</emphasis>
                Describes the standard images that the Yocto Project supports.
                </para></listitem>
            <listitem><para><emphasis>
                <link linkend='ref-features'>Features</link>:</emphasis>
                Describes mechanisms for creating distribution, machine, and image
                features during the build process using the OpenEmbedded build system.</para></listitem>
            <listitem><para><emphasis>
                <link linkend='ref-variables-glos'>Variables Glossary</link>:</emphasis>
                Presents most variables used by the OpenEmbedded build system, which
                uses BitBake.
                Entries describe the function of the variable and how to apply them.
                </para></listitem>
            <listitem><para><emphasis>
                <link linkend='ref-varlocality'>Variable Context</link>:</emphasis>
                Provides variable locality or context.</para></listitem>
            <listitem><para><emphasis>
                <link linkend='faq'>FAQ</link>:</emphasis>
                Provides answers for commonly asked questions in the Yocto Project
                development environment.</para></listitem>
            <listitem><para><emphasis>
                <link linkend='resources'>Contributing to the Yocto Project</link>:</emphasis>
                Provides guidance on how you can contribute back to the Yocto
                Project.</para></listitem>
        </itemizedlist>
    </para>
</section>


<section id='intro-requirements'>
<title>System Requirements</title>
    <para>
        For general Yocto Project system requirements, see the
        "<ulink url='&YOCTO_DOCS_QS_URL;#yp-resources'>What You Need and How You Get It</ulink>" section
        in the Yocto Project Quick Start.
        The remainder of this section provides details on system requirements
        not covered in the Yocto Project Quick Start.
    </para>

    <section id='detailed-supported-distros'>
        <title>Supported Linux Distributions</title>

        <para>
            Currently, the Yocto Project is supported on the following
            distributions:
            <note>
                <para>
                    Yocto Project releases are tested against the stable Linux
                    distributions in the following list.
                    The Yocto Project should work on other distributions but
                    validation is not performed against them.
                </para>

                <para>
                    In particular, the Yocto Project does not support
                    and currently has no plans to support
                    rolling-releases or development distributions due to their
                    constantly changing nature.
                    We welcome patches and bug reports, but keep in mind that
                    our priority is on the supported platforms listed below.
                </para>

                <para>
                    If you encounter problems, please go to
                    <ulink url='&YOCTO_BUGZILLA_URL;'>Yocto Project Bugzilla</ulink>
                    and submit a bug.
                    We are interested in hearing about your experience.
                </para>
            </note>
            <itemizedlist>
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            </itemizedlist>
        </para>

        <note>
            While the Yocto Project Team attempts to ensure all Yocto Project
            releases are one hundred percent compatible with each officially
            supported Linux distribution, instances might exist where you
            encounter a problem while using the Yocto Project on a specific
            distribution.
            For example, the CentOS 6.4 distribution does not include the
            Gtk+ 2.20.0 and PyGtk 2.21.0 (or higher) packages, which are
            required to run
            <ulink url='&YOCTO_HOME_URL;/tools-resources/projects/hob'>Hob</ulink>.
        </note>
    </section>

    <section id='required-packages-for-the-host-development-system'>
    <title>Required Packages for the Host Development System</title>

        <para>
            The list of packages you need on the host development system can
            be large when covering all build scenarios using the Yocto Project.
            This section provides required packages according to
            Linux distribution and function.
        </para>

        <section id='ubuntu-packages'>
            <title>Ubuntu and Debian</title>

            <para>
                The following list shows the required packages by function
                given a supported Ubuntu or Debian Linux distribution:
                <itemizedlist>
                    <listitem><para><emphasis>Essentials:</emphasis>
                        Packages needed to build an image on a headless
                        system:
                        <literallayout class='monospaced'>
     $ sudo apt-get install &UBUNTU_HOST_PACKAGES_ESSENTIAL;
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Graphical and Eclipse Plug-In Extras:</emphasis>
                        Packages recommended if the host system has graphics
                        support or if you are going to use the Eclipse
                        IDE:
                        <literallayout class='monospaced'>
     $ sudo apt-get install libsdl1.2-dev xterm
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Documentation:</emphasis>
                        Packages needed if you are going to build out the
                        Yocto Project documentation manuals:
                        <literallayout class='monospaced'>
     $ sudo apt-get install make xsltproc docbook-utils fop dblatex xmlto
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>ADT Installer Extras:</emphasis>
                        Packages needed if you are going to be using the
                        <ulink url='&YOCTO_DOCS_ADT_URL;#using-the-adt-installer'>Application Development Toolkit (ADT) Installer</ulink>:
                        <literallayout class='monospaced'>
     $ sudo apt-get install autoconf automake libtool libglib2.0-dev
                        </literallayout></para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='fedora-packages'>
            <title>Fedora Packages</title>

            <para>
                The following list shows the required packages by function
                given a supported Fedora Linux distribution:
                <itemizedlist>
                    <listitem><para><emphasis>Essentials:</emphasis>
                        Packages needed to build an image for a headless
                        system:
                        <literallayout class='monospaced'>
     $ sudo yum install &FEDORA_HOST_PACKAGES_ESSENTIAL;
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Graphical and Eclipse Plug-In Extras:</emphasis>
                        Packages recommended if the host system has graphics
                        support or if you are going to use the Eclipse
                        IDE:
                        <literallayout class='monospaced'>
     $ sudo yum install SDL-devel xterm perl-Thread-Queue
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Documentation:</emphasis>
                        Packages needed if you are going to build out the
                        Yocto Project documentation manuals:
                        <literallayout class='monospaced'>
     $ sudo yum install make docbook-style-dsssl docbook-style-xsl \
     docbook-dtds docbook-utils fop libxslt dblatex xmlto xsltproc
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>ADT Installer Extras:</emphasis>
                        Packages needed if you are going to be using the
                        <ulink url='&YOCTO_DOCS_ADT_URL;#using-the-adt-installer'>Application Development Toolkit (ADT) Installer</ulink>:
                        <literallayout class='monospaced'>
     $ sudo yum install autoconf automake libtool glib2-devel
                        </literallayout></para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='opensuse-packages'>
            <title>openSUSE Packages</title>

            <para>
                The following list shows the required packages by function
                given a supported openSUSE Linux distribution:
                <itemizedlist>
                    <listitem><para><emphasis>Essentials:</emphasis>
                        Packages needed to build an image for a headless
                        system:
                        <literallayout class='monospaced'>
     $ sudo zypper install &OPENSUSE_HOST_PACKAGES_ESSENTIAL;
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Graphical and Eclipse Plug-In Extras:</emphasis>
                        Packages recommended if the host system has graphics
                        support or if you are going to use the Eclipse
                        IDE:
                        <literallayout class='monospaced'>
     $ sudo zypper install libSDL-devel xterm
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Documentation:</emphasis>
                        Packages needed if you are going to build out the
                        Yocto Project documentation manuals:
                        <literallayout class='monospaced'>
     $ sudo zypper install make fop xsltproc dblatex xmlto
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>ADT Installer Extras:</emphasis>
                        Packages needed if you are going to be using the
                        <ulink url='&YOCTO_DOCS_ADT_URL;#using-the-adt-installer'>Application Development Toolkit (ADT) Installer</ulink>:
                        <literallayout class='monospaced'>
     $ sudo zypper install autoconf automake libtool glib2-devel
                        </literallayout></para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='centos-packages'>
            <title>CentOS Packages</title>

            <para>
                The following list shows the required packages by function
                given a supported CentOS Linux distribution:
                <note>
                    For CentOS 6.x, some of the versions of the components
                    provided by the distribution are too old (e.g. Git, Python,
                    and tar).
                    It is recommended that you install the buildtools in order
                    to provide versions that will work with the OpenEmbedded
                    build system.
                    For information on how to install the buildtools tarball,
                    see the
                    "<link linkend='required-git-tar-and-python-versions'>Required Git, Tar, and Python Versions</link>"
                    section.
                </note>
                <itemizedlist>
                    <listitem><para><emphasis>Essentials:</emphasis>
                        Packages needed to build an image for a headless
                        system:
                        <literallayout class='monospaced'>
     $ sudo yum install &CENTOS_HOST_PACKAGES_ESSENTIAL;
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Graphical and Eclipse Plug-In Extras:</emphasis>
                        Packages recommended if the host system has graphics
                        support or if you are going to use the Eclipse
                        IDE:
                        <literallayout class='monospaced'>
     $ sudo yum install SDL-devel xterm
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Documentation:</emphasis>
                        Packages needed if you are going to build out the
                        Yocto Project documentation manuals:
                        <literallayout class='monospaced'>
     $ sudo yum install make docbook-style-dsssl docbook-style-xsl \
     docbook-dtds docbook-utils fop libxslt dblatex xmlto xsltproc
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>ADT Installer Extras:</emphasis>
                        Packages needed if you are going to be using the
                        <ulink url='&YOCTO_DOCS_ADT_URL;#using-the-adt-installer'>Application Development Toolkit (ADT) Installer</ulink>:
                        <literallayout class='monospaced'>
     $ sudo yum install autoconf automake libtool glib2-devel
                        </literallayout></para></listitem>
                </itemizedlist>
            </para>
        </section>
    </section>

    <section id='required-git-tar-and-python-versions'>
        <title>Required Git, tar, and Python Versions</title>

        <para>
            In order to use the build system, your host development system
            must meet the following version requirements for Git, tar, and
            Python:
            <itemizedlist>
                <listitem><para>Git 1.7.8 or greater</para></listitem>
                <listitem><para>tar 1.24 or greater</para></listitem>
                <listitem><para>Python 2.7.3 or greater not including
                    Python 3.x, which is not supported.</para></listitem>
            </itemizedlist>
        </para>

        <para>
            If your host development system does not meet all these requirements,
            you can resolve this by installing a <filename>buildtools</filename>
            tarball that contains these tools.
            You can get the tarball one of two ways: download a pre-built
            tarball or use BitBake to build the tarball.
        </para>

        <section id='downloading-a-pre-built-buildtools-tarball'>
            <title>Downloading a Pre-Built <filename>buildtools</filename> Tarball</title>

            <para>
                Downloading and running a pre-built buildtools installer is
                the easiest of the two methods by which you can get these tools:
                <orderedlist>
                    <listitem><para>
                        Locate and download the <filename>*.sh</filename> at
                        <ulink url='&YOCTO_DL_URL;/releases/yocto/yocto-&DISTRO;/buildtools/'></ulink>.
                        </para></listitem>
                    <listitem><para>
                        Execute the installation script.
                        Here is an example:
                        <literallayout class='monospaced'>
     $ sh poky-glibc-x86_64-buildtools-tarball-x86_64-buildtools-nativesdk-standalone-&DISTRO;.sh
                        </literallayout>
                        During execution, a prompt appears that allows you to
                        choose the installation directory.
                        For example, you could choose the following:
                        <literallayout class='monospaced'>
     /home/<replaceable>your-username</replaceable>/buildtools
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        Source the tools environment setup script by using a
                        command like the following:
                        <literallayout class='monospaced'>
     $ source /home/<replaceable>your_username</replaceable>/buildtools/environment-setup-i586-poky-linux
                        </literallayout>
                        Of course, you need to supply your installation directory and be
                        sure to use the right file (i.e. i585 or x86-64).
                        </para>
                        <para>
                        After you have sourced the setup script,
                        the tools are added to <filename>PATH</filename>
                        and any other environment variables required to run the
                        tools are initialized.
                        The results are working versions versions of Git, tar,
                        Python and <filename>chrpath</filename>.
                        </para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='building-your-own-buildtools-tarball'>
            <title>Building Your Own <filename>buildtools</filename> Tarball</title>

            <para>
                Building and running your own buildtools installer applies
                only when you have a build host that can already run BitBake.
                In this case, you use that machine to build the
                <filename>.sh</filename> file and then
                take steps to transfer and run it on a
                machine that does not meet the minimal Git, tar, and Python
                requirements.
            </para>

            <para>
                Here are the steps to take to build and run your own
                buildtools installer:
                <orderedlist>
                    <listitem><para>
                        On the machine that is able to run BitBake,
                        be sure you have set up your build environment with
                        the setup script
                        (<link linkend='structure-core-script'><filename>&OE_INIT_FILE;</filename></link>
                        or
                        <link linkend='structure-memres-core-script'><filename>oe-init-build-env-memres</filename></link>).
                        </para></listitem>
                    <listitem><para>
                        Run the BitBake command to build the tarball:
                        <literallayout class='monospaced'>
     $ bitbake buildtools-tarball
                        </literallayout>
                        <note>
                        The
                        <link linkend='var-SDKMACHINE'><filename>SDKMACHINE</filename></link>
                        variable in your <filename>local.conf</filename> file
                        determines whether you build tools for a 32-bit
                        or 64-bit system.
                       </note>
                       Once the build completes, you can find the
                       <filename>.sh</filename> file that installs
                       the tools in the <filename>tmp/deploy/sdk</filename>
                       subdirectory of the
                       <ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>.
                       The installer file has the string "buildtools"
                       in the name.
                       </para></listitem>
                   <listitem><para>
                       Transfer the <filename>.sh</filename> file from the
                       build host to the machine that does not meet the
                       Git, tar, or Python requirements.
                       </para></listitem>
                   <listitem><para>
                       On the machine that does not meet the requirements,
                       run the <filename>.sh</filename> file
                       to install the tools.
                       Here is an example:
                       <literallayout class='monospaced'>
     $ sh poky-glibc-x86_64-buildtools-tarball-x86_64-buildtools-nativesdk-standalone-&DISTRO;.sh
                       </literallayout>
                       During execution, a prompt appears that allows you to
                       choose the installation directory.
                       For example, you could choose the following:
                       <literallayout class='monospaced'>
     /home/<replaceable>your_username</replaceable>/buildtools
                       </literallayout>
                       </para></listitem>
                    <listitem><para>
                        Source the tools environment setup script by using a
                        command like the following:
                        <literallayout class='monospaced'>
     $ source /home/<replaceable>your_username</replaceable>/buildtools/environment-setup-i586-poky-linux
                        </literallayout>
                        Of course, you need to supply your installation directory and be
                        sure to use the right file (i.e. i585 or x86-64).
                        </para>
                        <para>
                        After you have sourced the setup script,
                        the tools are added to <filename>PATH</filename>
                        and any other environment variables required to run the
                        tools are initialized.
                        The results are working versions versions of Git, tar,
                        Python and <filename>chrpath</filename>.
                        </para></listitem>
                </orderedlist>
            </para>
        </section>
    </section>
</section>

<section id='intro-getit'>
    <title>Obtaining the Yocto Project</title>
    <para>
        The Yocto Project development team makes the Yocto Project available through a number
        of methods:
        <itemizedlist>
            <listitem><para><emphasis>Source Repositories:</emphasis>
                Working from a copy of the upstream
                <filename>poky</filename> repository is the
                preferred method for obtaining and using a Yocto Project
                release.
                You can view the Yocto Project Source Repositories at
                <ulink url='&YOCTO_GIT_URL;/cgit.cgi'></ulink>.
                In particular, you can find the
                <filename>poky</filename> repository at
                <ulink url='http://git.yoctoproject.org/cgit/cgit.cgi/poky/'></ulink>.
                </para></listitem>
            <listitem><para><emphasis>Releases:</emphasis> Stable, tested
                releases are available as tarballs through
                <ulink url='&YOCTO_DL_URL;/releases/yocto/'/>.</para></listitem>
            <listitem><para><emphasis>Nightly Builds:</emphasis> These
                tarball releases are available at
                <ulink url='&YOCTO_AB_NIGHTLY_URL;'/>.
                These builds include Yocto Project releases, meta-toolchain
                tarball installation scripts, and experimental builds.
                </para></listitem>
            <listitem><para><emphasis>Yocto Project Website:</emphasis> You can
                find tarball releases of the Yocto Project and supported BSPs
                at the
                <ulink url='&YOCTO_HOME_URL;'>Yocto Project website</ulink>.
                Along with these downloads, you can find lots of other
                information at this site.
                </para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='intro-getit-dev'>
    <title>Development Checkouts</title>
    <para>
        Development using the Yocto Project requires a local
        <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>.
        You can set up the Source Directory by cloning a copy of the upstream
        <ulink url='&YOCTO_DOCS_DEV_URL;#poky'>poky</ulink> Git repository.
        For information on how to do this, see the
        "<ulink url='&YOCTO_DOCS_DEV_URL;#getting-setup'>Getting Set Up</ulink>"
        section in the Yocto Project Development Manual.
    </para>
</section>

</chapter>
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