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

<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >

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

<section id='ref-welcome'>
    <title>Welcome</title>

    <para>
        Welcome to the Yocto Project Reference Manual.
        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.
    </para>

    <para>
        This reference manual is best used after you have an understanding
        of the basics of the Yocto Project.
        The manual is not meant to be read as a starting point to the
        Yocto Project.
        Use this manual to find concepts, variable definitions, class
        descriptions, and so forth.
        The manual augments working with the Yocto Project during application
        and kernel development.
    </para>

    <para>
        The Yocto Project Reference Manual does not provide "how-to",
        task-oriented information.
        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>.
        You can find "how-to" information in the
        <ulink url='&YOCTO_DOCS_DEV_URL;'>Yocto Project Development Manual</ulink>.
        <note><title>Tip</title>
            For more information about the Yocto Project Documentation set,
            see the
            "<link linkend='resources-links-and-related-documentation'>Links and Related Documentation</link>"
            section.
        </note>
    </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-devtool-reference'><filename>devtool</filename> Quick Reference</link>:
                </emphasis>
                Provides a quick reference for the <filename>devtool</filename>
                command.
                </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'>Contributions and Additional Information</link>:
                </emphasis>
                Provides an overview of methods by which you can
                contribute to and participate in 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'>Setting Up to Use the Yocto Project</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>
<!--
                <listitem><para>Ubuntu 10.04</para></listitem>
                <listitem><para>Ubuntu 11.10</para></listitem>
                <listitem><para>Ubuntu 12.04 (LTS)</para></listitem>
                <listitem><para>Ubuntu 13.10</para></listitem> -->
                <listitem><para>Ubuntu 14.04 (LTS)</para></listitem>
                <listitem><para>Ubuntu 14.10</para></listitem>
                <listitem><para>Ubuntu 15.04</para></listitem>
                <listitem><para>Ubuntu 15.10</para></listitem>
                <listitem><para>Ubuntu 16.04</para></listitem>
<!--                <listitem><para>Fedora 16 (Verne)</para></listitem>
                <listitem><para>Fedora 17 (Spherical)</para></listitem>
                <listitem><para>Fedora release 19 (Schrödinger's Cat)</para></listitem>
                <listitem><para>Fedora release 20 (Heisenbug)</para></listitem> -->
                <listitem><para>Fedora release 22</para></listitem>
                <listitem><para>Fedora release 23</para></listitem>
                <listitem><para>Fedora release 24</para></listitem>
<!--                <listitem><para>CentOS release 5.6 (Final)</para></listitem>
                <listitem><para>CentOS release 5.7 (Final)</para></listitem>
                <listitem><para>CentOS release 5.8 (Final)</para></listitem>
                <listitem><para>CentOS release 6.3 (Final)</para></listitem>
                <listitem><para>CentOS release 6.x</para></listitem> -->
                <listitem><para>CentOS release 7.x</para></listitem>
<!--                <listitem><para>Debian GNU/Linux 6.0 (Squeeze)</para></listitem>
                <listitem><para>Debian GNU/Linux 7.x (Wheezy)</para></listitem> -->
                <listitem><para>Debian GNU/Linux 8.x (Jessie)</para></listitem>
<!--                <listitem><para>Debian GNU/Linux 7.1 (Wheezy)</para></listitem>
                <listitem><para>Debian GNU/Linux 7.2 (Wheezy)</para></listitem>
                <listitem><para>Debian GNU/Linux 7.3 (Wheezy)</para></listitem>
                <listitem><para>Debian GNU/Linux 7.4 (Wheezy)</para></listitem>
                <listitem><para>Debian GNU/Linux 7.5 (Wheezy)</para></listitem>
                <listitem><para>Debian GNU/Linux 7.6 (Wheezy)</para></listitem> -->
<!--                <listitem><para>openSUSE 11.4</para></listitem>
                <listitem><para>openSUSE 12.1</para></listitem>
                <listitem><para>openSUSE 12.2</para></listitem>
                <listitem><para>openSUSE 12.3</para></listitem>
                <listitem><para>openSUSE 13.1</para></listitem> -->
                <listitem><para>openSUSE 13.2</para></listitem>
                <listitem><para>openSUSE 42.1</para></listitem>
            </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.
        </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:
                <note>
                    If your build system has the
                    <filename>oss4-dev</filename> package installed, you
                    might experience QEMU build failures due to the package
                    installing its own custom
                    <filename>/usr/include/linux/soundcard.h</filename> on
                    the Debian system.
                    If you run into this situation, either of the following
                    solutions exist:
                    <literallayout class='monospaced'>
     $ sudo apt-get build-dep qemu
     $ sudo apt-get remove oss4-dev
                    </literallayout>
                 </note>
                <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>OpenEmbedded Self-Test (<filename>oe-selftest</filename>):</emphasis>
                        Packages needed if you are going to run
                        <filename>oe-selftest</filename>:
                        <literallayout class='monospaced'>
     $ sudo apt-get install python-git
                        </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 dnf 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 dnf 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 dnf install make docbook-style-dsssl docbook-style-xsl \
     docbook-dtds docbook-utils fop libxslt dblatex xmlto xsltproc
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>OpenEmbedded Self-Test (<filename>oe-selftest</filename>):</emphasis>
                        Packages needed if you are going to run
                        <filename>oe-selftest</filename>:
                        <literallayout class='monospaced'>
     $ sudo dnf install python3-GitPython
                        </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>OpenEmbedded Self-Test (<filename>oe-selftest</filename>):</emphasis>
                        Packages needed if you are going to run
                        <filename>oe-selftest</filename>:
                        <literallayout class='monospaced'>
     $ sudo zypper install python-GitPython
                        </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; SDL-devel xterm
                        </literallayout>
                        <note><title>Notes</title>
                            <itemizedlist>
                                <listitem><para>
                                    Extra Packages for Enterprise Linux
                                    (i.e. <filename>epel-release</filename>)
                                    is a collection of packages from Fedora
                                    built on RHEL/CentOS for easy installation
                                    of packages not included in enterprise
                                    Linux by default.
                                    You need to install these packages
                                    separately.
                                    </para></listitem>
                                <listitem><para>
                                    The <filename>makecache</filename> command
                                    consumes additional Metadata from
                                    <filename>epel-release</filename>.
                                    </para></listitem>
                            </itemizedlist>
                        </note>
                        </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>OpenEmbedded Self-Test (<filename>oe-selftest</filename>):</emphasis>
                        Packages needed if you are going to run
                        <filename>oe-selftest</filename>:
                        <literallayout class='monospaced'>
     $ sudo yum install GitPython
                        </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 1.8.3.1 or greater</para></listitem>
                <listitem><para>tar 1.24 or greater</para></listitem>
                <listitem><para>Python 3.4.0 or greater</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
                       <link linkend='build-directory'>Build Directory</link>.
                       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, SDK 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>

<section id='yocto-project-terms'>
    <title>Yocto Project Terms</title>

    <para>
        Following is a list of terms and definitions users new to the Yocto
        Project development environment might find helpful.
        While some of these terms are universal, the list includes them
        just in case:
        <itemizedlist>
            <listitem><para>
                <emphasis>Append Files:</emphasis>
                Files that append build information to a recipe file.
                Append files are known as BitBake append files and
                <filename>.bbappend</filename> files.
                The OpenEmbedded build system expects every append file to have
                a corresponding recipe (<filename>.bb</filename>) file.
                Furthermore, the append file and corresponding recipe file
                must use the same root filename.
                The filenames can differ only in the file type suffix used
                (e.g.
                <filename>formfactor_0.0.bb</filename> and
                <filename>formfactor_0.0.bbappend</filename>).</para>

                <para>Information in append files extends or overrides the
                information in the similarly-named recipe file.
                For an example of an append file in use, see the
                "<ulink url='&YOCTO_DOCS_DEV_URL;#using-bbappend-files'>Using .bbappend Files</ulink>"
                section in the Yocto Project Development Manual.
                <note>
                    Append files can also use wildcard patterns in their
                    version numbers so they can be applied to more than one
                    version of the underlying recipe file.
                </note>
                </para></listitem>
            <listitem><para id='bitbake-term'>
                <emphasis>BitBake:</emphasis>
                The task executor and scheduler used by the OpenEmbedded build
                system to build images.
                For more information on BitBake, see the
                <ulink url='&YOCTO_DOCS_BB_URL;'>BitBake User Manual</ulink>.
                </para></listitem>
            <listitem>
                <para id='build-directory'>
                <emphasis>Build Directory:</emphasis>
                This term refers to the area used by the OpenEmbedded build
                system for builds.
                The area is created when you <filename>source</filename> the
                setup environment script that is found in the Source Directory
                (i.e. <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>).
                The
                <link linkend='var-TOPDIR'><filename>TOPDIR</filename></link>
                variable points to the Build Directory.</para>

                <para>You have a lot of flexibility when creating the Build
                Directory.
                Following are some examples that show how to create the
                directory.
                The examples assume your
                <link linkend='source-directory'>Source Directory</link> is
                named <filename>poky</filename>:
                <itemizedlist>
                    <listitem><para>Create the Build Directory inside your
                        Source Directory and let the name of the Build
                        Directory default to <filename>build</filename>:
                        <literallayout class='monospaced'>
     $ cd $HOME/poky
     $ source &OE_INIT_FILE;
                        </literallayout>
                        </para></listitem>
                    <listitem><para>Create the Build Directory inside your
                        home directory and specifically name it
                        <filename>test-builds</filename>:
                        <literallayout class='monospaced'>
     $ cd $HOME
     $ source poky/&OE_INIT_FILE; test-builds
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        Provide a directory path and specifically name the
                        Build Directory.
                        Any intermediate folders in the pathname must exist.
                        This next example creates a Build Directory named
                        <filename>YP-&POKYVERSION;</filename>
                        in your home directory within the existing
                        directory <filename>mybuilds</filename>:
                        <literallayout class='monospaced'>
     $cd $HOME
     $ source $HOME/poky/&OE_INIT_FILE; $HOME/mybuilds/YP-&POKYVERSION;
                        </literallayout>
                        </para></listitem>
                </itemizedlist>
                <note>
                    By default, the Build Directory contains
                    <link linkend='var-TMPDIR'><filename>TMPDIR</filename></link>,
                    which is a temporary directory the build system uses for
                    its work.
                    <filename>TMPDIR</filename> cannot be under NFS.
                    Thus, by default, the Build Directory cannot be under NFS.
                    However, if you need the Build Directory to be under NFS,
                    you can set this up by setting <filename>TMPDIR</filename>
                    in your <filename>local.conf</filename> file
                    to use a local drive.
                    Doing so effectively separates <filename>TMPDIR</filename>
                    from <filename>TOPDIR</filename>, which is the Build
                    Directory.
                </note>
                </para></listitem>
            <listitem><para>
                <emphasis>Classes:</emphasis>
                Files that provide for logic encapsulation and inheritance so
                that commonly used patterns can be defined once and then
                easily used in multiple recipes.
                For reference information on the Yocto Project classes, see the
                "<link linkend='ref-classes'>Classes</link>" chapter.
                Class files end with the <filename>.bbclass</filename>
                filename extension.
                </para></listitem>
            <listitem><para>
                <emphasis>Configuration File:</emphasis>
                Configuration information in various <filename>.conf</filename>
                files provides global definitions of variables.
                The <filename>conf/local.conf</filename> configuration file in
                the
                <link linkend='build-directory'>Build Directory</link>
                contains user-defined variables that affect every build.
                The <filename>meta-poky/conf/distro/poky.conf</filename>
                configuration file defines Yocto "distro" configuration
                variables used only when building with this policy.
                Machine configuration files, which
                are located throughout the
                <link linkend='source-directory'>Source Directory</link>, define
                variables for specific hardware and are only used when building
                for that target (e.g. the
                <filename>machine/beaglebone.conf</filename> configuration
                file defines variables for the Texas Instruments ARM Cortex-A8
                development board).
                Configuration files end with a <filename>.conf</filename>
                filename extension.
                </para></listitem>
            <listitem><para id='cross-development-toolchain'>
                <emphasis>Cross-Development Toolchain:</emphasis>
                In general, a cross-development toolchain is a collection of
                software development tools and utilities that run on one
                architecture and allow you to develop software for a
                different, or targeted, architecture.
                These toolchains contain cross-compilers, linkers, and
                debuggers that are specific to the target architecture.</para>

                <para>The Yocto Project supports two different cross-development
                toolchains:
                <itemizedlist>
                    <listitem><para>
                        A toolchain only used by and within
                        BitBake when building an image for a target
                        architecture.
                        </para></listitem>
                    <listitem><para>A relocatable toolchain used outside of
                        BitBake by developers when developing applications
                        that will run on a targeted device.
                        </para></listitem>
                </itemizedlist></para>

                <para>Creation of these toolchains is simple and automated.
                For information on toolchain concepts as they apply to the
                Yocto Project, see the
                "<link linkend='cross-development-toolchain-generation'>Cross-Development Toolchain Generation</link>"
                section.
                You can also find more information on using the
                relocatable toolchain in the
                <ulink url='&YOCTO_DOCS_SDK_URL;'>Yocto Project Software Development Kit (SDK) Developer's Guide</ulink>.
                </para></listitem>
            <listitem><para>
                <emphasis>Image:</emphasis>
                An image is an artifact of the BitBake build process given
                a collection of recipes and related Metadata.
                Images are the binary output that run on specific hardware or
                QEMU and are used for specific use-cases.
                For a list of the supported image types that the Yocto Project
                provides, see the
                "<link linkend='ref-images'>Images</link>"
                chapter.
                </para></listitem>
            <listitem><para>
                <emphasis>Layer:</emphasis>
                A collection of recipes representing the core,
                a BSP, or an application stack.
                For a discussion specifically on BSP Layers, see the
                "<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>"
                section in the Yocto Project Board Support Packages (BSP)
                Developer's Guide.
                </para></listitem>
            <listitem><para id='metadata'>
                <emphasis>Metadata:</emphasis>
                The files that BitBake parses when building an image.
                In general, Metadata includes recipes, classes, and
                configuration files.
                In the context of the kernel ("kernel Metadata"),
                it refers to Metadata in the <filename>meta</filename>
                branches of the kernel source Git repositories.
                </para></listitem>
            <listitem><para id='oe-core'>
                <emphasis>OE-Core:</emphasis>
                A core set of Metadata originating with OpenEmbedded (OE)
                that is shared between OE and the Yocto Project.
                This Metadata is found in the <filename>meta</filename>
                directory of the
                <link linkend='source-directory'>Source Directory</link>.
                </para></listitem>
            <listitem><para id='build-system-term'>
                <emphasis>OpenEmbedded Build System:</emphasis>
                The build system specific to the Yocto Project.
                The OpenEmbedded build system is based on another project known
                as "Poky", which uses
                <link linkend='bitbake-term'>BitBake</link> as the task
                executor.
                Throughout the Yocto Project documentation set, the
                OpenEmbedded build system is sometimes referred to simply
                as "the build system".
                If other build systems, such as a host or target build system
                are referenced, the documentation clearly states the
                difference.
                <note>
                    For some historical information about Poky, see the
                    <link linkend='poky'>Poky</link> term.
                </note>
                </para></listitem>
            <listitem><para>
                <emphasis>Package:</emphasis>
                In the context of the Yocto Project, this term refers to a
                recipe's packaged output produced by BitBake (i.e. a
                "baked recipe").
                A package is generally the compiled binaries produced from the
                recipe's sources.
                You "bake" something by running it through BitBake.</para>

                <para>It is worth noting that the term "package" can,
                in general, have subtle meanings.
                For example, the packages referred to in the
                "<ulink url='&YOCTO_DOCS_QS_URL;#packages'>The Build Host Packages</ulink>"
                section in the Yocto Project Quick Start are compiled binaries
                that, when installed, add functionality to your Linux
                distribution.</para>

                <para>Another point worth noting is that historically within
                the Yocto Project, recipes were referred to as packages - thus,
                the existence of several BitBake variables that are seemingly
                mis-named,
                (e.g. <link linkend='var-PR'><filename>PR</filename></link>,
                <link linkend='var-PV'><filename>PV</filename></link>, and
                <link linkend='var-PE'><filename>PE</filename></link>).
                </para></listitem>
            <listitem><para>
                <emphasis>Package Groups:</emphasis>
                Arbitrary groups of software Recipes.
                You use package groups to hold recipes that, when built,
                usually accomplish a single task.
                For example, a package group could contain the recipes for a
                company’s proprietary or value-add software.
                Or, the package group could contain the recipes that enable
                graphics.
                A package group is really just another recipe.
                Because package group files are recipes, they end with the
                <filename>.bb</filename> filename extension.
                </para></listitem>
            <listitem><para id='poky'>
                <emphasis>Poky:</emphasis>
                The term "poky" can mean several things.
                In its most general sense, it is an open-source
                project that was initially developed by OpenedHand.
                With OpenedHand, poky was developed off of the existing
                OpenEmbedded build system becoming a commercially
                supportable build system for embedded Linux.
                After Intel Corporation acquired OpenedHand, the
                project poky became the basis for the Yocto Project's
                build system.</para>

                <para>Within the Yocto Project source repositories,
                <filename>poky</filename> exists as a separate Git
                repository you can clone to yield a local copy on your
                host system.
                Thus, "poky" can refer to the local copy of the Source
                Directory used for development within the Yocto
                Project.</para>

                <para>Finally, "poky" can refer to the default
                <link linkend='var-DISTRO'><filename>DISTRO</filename></link>
                (i.e. distribution) created when you use the Yocto
                Project in conjunction with the
                <filename>poky</filename> repository to build an image.
                </para></listitem>
            <listitem><para>
                <emphasis>Recipe:</emphasis>
                A set of instructions for building packages.
                A recipe describes where you get source code, which patches
                to apply, how to configure the source, how to compile it and so on.
                Recipes also describe dependencies for libraries or for other
                recipes.
                Recipes represent the logical unit of execution, the software
                to build, the images to build, and use the
                <filename>.bb</filename> file extension.
                </para></listitem>
            <listitem>
                <para id='source-directory'>
                <emphasis>Source Directory:</emphasis>
                This term refers to the directory structure created as a result
                of creating a local copy of the <filename>poky</filename> Git
                repository <filename>git://git.yoctoproject.org/poky</filename>
                or expanding a released <filename>poky</filename> tarball.
                <note>
                    Creating a local copy of the <filename>poky</filename>
                    Git repository is the recommended method for setting up
                    your Source Directory.
                </note>
                Sometimes you might hear the term "poky directory" used to refer
                to this directory structure.
                <note>
                    The OpenEmbedded build system does not support file or
                    directory names that contain spaces.
                    Be sure that the Source Directory you use does not contain
                    these types of names.
                </note></para>

                <para>The Source Directory contains BitBake, Documentation,
                Metadata and other files that all support the Yocto Project.
                Consequently, you must have the Source Directory in place on
                your development system in order to do any development using
                the Yocto Project.</para>

                <para>When you create a local copy of the Git repository, you
                can name the repository anything you like.
                Throughout much of the documentation, "poky"
                is used as the name of the top-level folder of the local copy of
                the poky Git repository.
                So, for example, cloning the <filename>poky</filename> Git
                repository results in a local Git repository whose top-level
                folder is also named "poky".</para>

                <para>While it is not recommended that you use tarball expansion
                to set up the Source Directory, if you do, the top-level
                directory name of the Source Directory is derived from the
                Yocto Project release tarball.
                For example, downloading and unpacking
                <filename>&YOCTO_POKY_TARBALL;</filename> results in a
                Source Directory whose root folder is named
                <filename>&YOCTO_POKY;</filename>.</para>

                <para>It is important to understand the differences between the
                Source Directory created by unpacking a released tarball as
                compared to cloning
                <filename>git://git.yoctoproject.org/poky</filename>.
                When you unpack a tarball, you have an exact copy of the files
                based on the time of release - a fixed release point.
                Any changes you make to your local files in the Source Directory
                are on top of the release and will remain local only.
                On the other hand, when you clone the <filename>poky</filename>
                Git repository, you have an active development repository with
                access to the upstream repository's branches and tags.
                In this case, any local changes you make to the local
                Source Directory can be later applied to active development
                branches of the upstream <filename>poky</filename> Git
                repository.</para>

                <para>For more information on concepts related to Git
                repositories, branches, and tags, see the
                "<link linkend='repositories-tags-and-branches'>Repositories, Tags, and Branches</link>"
                section.
                </para></listitem>
            <listitem><para><emphasis>Task:</emphasis>
                A unit of execution for BitBake (e.g.
                <link linkend='ref-tasks-compile'><filename>do_compile</filename></link>,
                <link linkend='ref-tasks-fetch'><filename>do_fetch</filename></link>,
                <link linkend='ref-tasks-patch'><filename>do_patch</filename></link>,
                and so forth).
                </para></listitem>
            <listitem><para>
                <emphasis>Upstream:</emphasis>
                A reference to source code or repositories
                that are not local to the development system but located in a
                master area that is controlled by the maintainer of the source
                code.
                For example, in order for a developer to work on a particular
                piece of code, they need to first get a copy of it from an
                "upstream" source.
                </para></listitem>
        </itemizedlist>
    </para>
</section>

</chapter>
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