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<chapter id='dev-manual-start'>

<title>Getting Started with the Yocto Project</title>

<para>
    This chapter provides procedures related to getting set up to use the
    Yocto Project, working with Yocto Project source files, and building
    an image.
</para>

<section id='setting-up-the-development-host-to-use-the-yocto-project'>
    <title>Setting Up the Development Host to Use the Yocto Project</title>

    <para>
        This section provides procedures to set up your development host to
        use the Yocto Project.
        You can use the Yocto Project on a native Linux development host or
        you can use
        <ulink url='https://git.yoctoproject.org/cgit/cgit.cgi/crops/about/'>CROPS</ulink>,
        which leverages
        <ulink url='https://www.docker.com/'>Docker Containers</ulink>,
        to prepare any Linux, Mac, or Windows development host.
    </para>

    <para>
        Once your development host is set up to use the Yocto Project,
        further steps are necessary depending on what you want to
        accomplish.
        See the following references for information on how to prepare for
        Board Support Package (BSP) development, kernel development, and
        development using the <trademark class='trade'>Eclipse</trademark> IDE:
        <itemizedlist>
            <listitem><para>
                <emphasis>BSP Development:</emphasis>
                See the
                "<ulink url='&YOCTO_DOCS_BSP_URL;#preparing-your-build-host-to-work-with-bsp-layers'>Preparing Your Build Host to Work With BSP Layers</ulink>"
                section in the Yocto Project Board Support Package (BSP)
                Developer's Guide.
                </para></listitem>
            <listitem><para>
                <emphasis>Kernel Development:</emphasis>
                See the
                "<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#preparing-the-build-host-to-work-on-the-kernel'>Preparing the Build Host to Work on the Kernel</ulink>"
                section in the Yocto Project Linux Kernel Development Manual.
                </para></listitem>
            <listitem><para>
                <emphasis>Eclipse Development:</emphasis>
                See the
                "<ulink url='&YOCTO_DOCS_SDK_URL;#sdk-eclipse-project'>Developing Applications Using <trademark class='trade'>Eclipse</trademark></ulink>"
                Chapter in the Yocto Project Application Development and the
                Extensible Software Development Kit (eSDK) manual.
                </para></listitem>
        </itemizedlist>
    </para>

    <section id='setting-up-a-native-linux-host'>
        <title>Setting Up a Native Linux Host</title>

        <para>
            Follow these steps to prepare a native Linux machine as your
            Yocto Project development host:
            <orderedlist>
                <listitem><para>
                    <emphasis>Use a Supported Linux Distribution:</emphasis>
                    You should have a reasonably current Linux-based host
                    system.
                    You will have the best results with a recent release of
                    Fedora, openSUSE, Debian, Ubuntu, or CentOS as these
                    releases are frequently tested against the Yocto Project
                    and officially supported.
                    For a list of the distributions under validation and their
                    status, see the
                    "<ulink url='&YOCTO_DOCS_REF_URL;#detailed-supported-distros'>Supported Linux Distributions</ulink>" section
                    in the Yocto Project Reference Manual and the wiki page at
                    <ulink url='&YOCTO_WIKI_URL;/wiki/Distribution_Support'>Distribution Support</ulink>.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Have Enough Free Memory:</emphasis>
                    You should have at least 50 Gbytes of free disk space
                    for building images.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Meet Minimal Version Requirements:</emphasis>
                    The OpenEmbedded build system should be able to run on any
                    modern distribution that has the following versions for
                    Git, tar, and Python.
                    <itemizedlist>
                        <listitem><para>
                            Git 1.8.3.1 or greater
                            </para></listitem>
                        <listitem><para>
                            tar 1.27 or greater
                            </para></listitem>
                        <listitem><para>
                            Python 3.4.0 or greater.
                            </para></listitem>
                    </itemizedlist>
                    If your build host does not meet any of these three listed
                    version requirements, you can take steps to prepare the
                    system so that you can still use the Yocto Project.
                    See the
                    "<ulink url='&YOCTO_DOCS_REF_URL;#required-git-tar-and-python-versions'>Required Git, tar, and Python Versions</ulink>"
                    section in the Yocto Project Reference Manual for
                    information.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Install Development Host Packages:</emphasis>
                    Required development host packages vary depending on your
                    build machine and what you want to do with the Yocto
                    Project.
                    Collectively, the number of required packages is large
                    if you want to be able to cover all cases.</para>

                    <para>For lists of required packages for all scenarios,
                    see the
                    "<ulink url='&YOCTO_DOCS_REF_URL;#required-packages-for-the-host-development-system'>Required Packages for the Host Development System</ulink>"
                    section in the Yocto Project Reference Manual.
                    </para></listitem>
            </orderedlist>
            Once you have completed the previous steps, you are ready to
            continue using a given development path on your native Linux
            machine.
            If you are going to use BitBake, see the
            "<link linkend='cloning-the-poky-repository'>Cloning the <filename>poky</filename> Repository</link>"
            section.
            If you are going to use the Extensible SDK, see the
            "<ulink url='&YOCTO_DOCS_SDK_URL;#sdk-extensible'>Using the Extensible SDK</ulink>"
            Chapter in the Yocto Project Application Development and the
            Extensible Software Development Kit (eSDK) manual.
            If you want to work on the kernel, see the
            <ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;'>Yocto Project Linux Kernel Development Manual</ulink>.
            If you are going to use Toaster, see the
            "<ulink url='&YOCTO_DOCS_TOAST_URL;#toaster-manual-setup-and-use'>Setting Up and Using Toaster</ulink>"
            section in the Toaster User Manual.
        </para>
    </section>

    <section id='setting-up-to-use-crops'>
        <title>Setting Up to Use CROss PlatformS (CROPS)</title>

        <para>
            With
            <ulink url='https://git.yoctoproject.org/cgit/cgit.cgi/crops/about/'>CROPS</ulink>,
            which leverages
            <ulink url='https://www.docker.com/'>Docker Containers</ulink>,
            you can create a Yocto Project development environment that
            is operating system agnostic.
            You can set up a container in which you can develop using the
            Yocto Project on a Windows, Mac, or Linux  machine.
        </para>

        <para>
            Follow these general steps to prepare a Windows, Mac, or Linux
            machine as your Yocto Project development host:
            <orderedlist>
                <listitem><para>
                    <emphasis>Go to the Docker Installation Site:</emphasis>
                    <ulink url='https://www.docker.com/what-docker'>Docker</ulink>
                    is a software container platform that you need to install
                    on the host development machine.
                    To start the installation process, see the
                    <ulink url='https://docs.docker.com/engine/installation/'>Docker Installation</ulink>
                    site.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Choose Your Docker Edition:</emphasis>
                    Docker comes in several editions.
                    For the Yocto Project, the stable community edition
                    (i.e. "Docker CE Stable") is adequate.
                    You can learn more about the Docker editions from the
                    site.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Go the Install Site for Your Platform:</emphasis>
                    Click the link for the Docker edition associated with
                    your development host machine's native software.
                    For example, if your machine is running Microsoft
                    Windows Version 10 and you want the Docker CE Stable
                    edition, click that link under "Supported Platforms".
                    </para></listitem>
                <listitem><para>
                    <emphasis>Understand What You Need:</emphasis>
                    The install page has pre-requisites your machine must
                    meet.
                    Be sure you read through this page and make sure your
                    machine meets the requirements to run Docker.
                    If your machine does not meet the requirements, the page
                    has instructions to handle exceptions.
                    For example, to run Docker on Windows 10, you must have
                    the pro version of the operating system.
                    If you have the home version, you need to install the
                    <ulink url='https://docs.docker.com/toolbox/overview/#ready-to-get-started'>Docker Toolbox</ulink>.
                    </para>

                    <para>Another example is that a Windows machine needs to
                    have Microsoft Hyper-V.
                    If you have a legacy version of the the Microsoft
                    operating system or for any other reason you do not have
                    Microsoft Hyper-V, you would have to enter the BIOS and
                    enable virtualization.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Install the Software:</emphasis>
                    Once you have understood all the pre-requisites, you can
                    download and install the appropriate software.
                    Follow the instructions for your specific machine and
                    the type of the software you need to install.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Optionally Orient Yourself With Dockers:</emphasis>
                    If you are unfamiliar with Dockers and the container
                    concept, you can learn more here -
                    <ulink url='https://docs.docker.com/get-started/'></ulink>.
                    You should be able to launch Docker or the Docker Toolbox
                    and have a terminal shell on your development host.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Set Up the Containers to Use the Yocto Project:</emphasis>
                    Go to
                    <ulink url='https://github.com/crops/docker-win-mac-docs/wiki'></ulink>
                    and follow the directions for your particular
                    development host (i.e. Linux, Mac, or Windows).</para>

                    <para>Once you complete the setup instructions for your
                    machine, you have the Poky, Extensible SDK, and Toaster
                    containers available.
                    You can click those links from the page and learn more
                    about using each of those containers.
                    </para></listitem>
            </orderedlist>
            Once you have a container set up, everything is in place to
            develop just as if you were running on a native Linux machine.
            If you are going to use the Poky container, see the
            "<link linkend='cloning-the-poky-repository'>Cloning the <filename>poky</filename> Repository</link>"
            section.
            If you are going to use the Extensible SDK container, see the
            "<ulink url='&YOCTO_DOCS_SDK_URL;#sdk-extensible'>Using the Extensible SDK</ulink>"
            Chapter in the Yocto Project Application Development and the
            Extensible Software Development Kit (eSDK) manual.
            If you are going to use the Toaster container, see the
            "<ulink url='&YOCTO_DOCS_TOAST_URL;#toaster-manual-setup-and-use'>Setting Up and Using Toaster</ulink>"
            section in the Toaster User Manual.
        </para>
    </section>
</section>

<section id='working-with-yocto-project-source-files'>
    <title>Working With Yocto Project Source Files</title>

    <para>
        This section contains procedures related to locating and securing
        Yocto Project files.
        You establish and use these local files to work on projects.
        <note><title>Notes</title>
            <itemizedlist>
                <listitem><para>
                    For concepts and introductory information about Git as it
                    is used in the Yocto Project, see the
                    "<ulink url='&YOCTO_DOCS_GS_URL;#git'>Git</ulink>"
                    section in the Yocto Project Overview Manual.
                    </para></listitem>
                <listitem><para>
                    For concepts on Yocto Project source repositories, see the
                    "<ulink url='&YOCTO_DOCS_GS_URL;#yocto-project-repositories'>Yocto Project Source Repositories</ulink>"
                    section in the Yocto Project Overview Manual."
                    </para></listitem>
            </itemizedlist>
        </note>
    </para>

    <section id='accessing-source-repositories'>
        <title>Accessing Source Repositories</title>

        <para>
            Working from a copy of the upstream Yocto Project
            <ulink url='&YOCTO_DOCS_GS_URL;#source-repositories'>Source Repositories</ulink>
            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>

        <para>
            Use the following procedure to locate the latest upstream copy of
            the <filename>poky</filename> Git repository:
            <orderedlist>
                <listitem><para>
                    <emphasis>Access Repositories:</emphasis>
                    Open a browser and go to
                    <ulink url='&YOCTO_GIT_URL;'></ulink> to access the
                    GUI-based interface into the Yocto Project source
                    repositories.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Select the Repository:</emphasis>
                    Click on the repository in which you are interested (i.e.
                    <filename>poky</filename>).
                    </para></listitem>
                <listitem><para>
                    <emphasis>Find the URL Used to Clone the Repository:</emphasis>
                    At the bottom of the page, note the URL used to
                    <ulink url='&YOCTO_DOCS_GS_URL;#git-commands-clone'>clone</ulink>
                    that repository (e.g.
                    <filename>&YOCTO_GIT_URL;/poky</filename>).
                    <note>
                        For information on cloning a repository, see the
                        "<link linkend='cloning-the-poky-repository'>Cloning the <filename>poky</filename> Repository</link>"
                        section.
                    </note>
                    </para></listitem>
            </orderedlist>
        </para>
    </section>

    <section id='accessing-index-of-releases'>
        <title>Accessing Index of Releases</title>

        <para>
            Yocto Project maintains an Index of Releases area that contains
            related files that contribute to the Yocto Project.
            Rather than Git repositories, these files are tarballs that
            represent snapshots in time of a given component.
            <note><title>Tip</title>
                The recommended method for accessing Yocto Project
                components is to use Git to clone the upstream repository and
                work from within that locally cloned repository.
                The procedure in this section exists should you desire a
                tarball snapshot of any given component.
            </note>
            <orderedlist>
                <listitem><para>
                    <emphasis>Access the Index of Releases:</emphasis>
                    Open a browser and go to
                    <ulink url='&YOCTO_DL_URL;/releases'></ulink> to access the
                    Index of Releases.
                    The list represents released components (e.g.
                    <filename>eclipse-plugin</filename>,
                    <filename>sato</filename>, and so on).
                    <note>
                        The <filename>yocto</filename> directory contains the
                        full array of released Poky tarballs.
                        The <filename>poky</filename> directory in the
                        Index of Releases was historically used for very
                        early releases and exists now only for retroactive
                        completeness.
                    </note>
                    </para></listitem>
                <listitem><para>
                    <emphasis>Select a Component:</emphasis>
                    Click on any released component in which you are interested
                    (e.g. <filename>yocto</filename>).
                    </para></listitem>
                <listitem><para>
                    <emphasis>Find the Tarball:</emphasis>
                    Drill down to find the associated tarball.
                    For example, click on <filename>yocto-&DISTRO;</filename> to
                    view files associated with the Yocto Project &DISTRO;
                    release (e.g. <filename>poky-&DISTRO_NAME_NO_CAP;-&POKYVERSION;.tar.bz2</filename>,
                    which is the released Poky tarball).
                    </para></listitem>
                <listitem><para>
                    <emphasis>Download the Tarball:</emphasis>
                    Click the tarball to download and save a snapshot of the
                    given component.
                    </para></listitem>
            </orderedlist>
        </para>
    </section>

    <section id='using-the-downloads-page'>
        <title>Using the Downloads Page</title>

        <para>
            The
            <ulink url='&YOCTO_HOME_URL;'>Yocto Project Website</ulink>
            uses a "Downloads" area from which you can locate and download
            tarballs of any Yocto Project release.
            Rather than Git repositories, these files represent snapshot
            tarballs.
            <note><title>Tip</title>
                The recommended method for accessing Yocto Project
                components is to use Git to clone a repository and work from
                within that local repository.
                The procedure in this section exists should you desire a
                tarball snapshot of any given component.
            </note>
            <orderedlist>
                <listitem><para>
                    <emphasis>Go to the Yocto Project Website:</emphasis>
                    Open The
                    <ulink url='&YOCTO_HOME_URL;'>Yocto Project Website</ulink>
                    in your browser.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Get to the Downloads Area:</emphasis>
                    Click the "Downloads" tab.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Select the Type of Files:</emphasis>
                    Click the type of files you want such as "Build System",
                    "Tools", or "Board Support Packages (BSPs)".
                    </para></listitem>
                <listitem><para>
                    <emphasis>Locate and Download the Tarball:</emphasis>
                    From the list of releases, locate the appropriate
                    download link and download the files.
                    </para></listitem>
            </orderedlist>
        </para>
    </section>

    <section id='accessing-nightly-builds'>
        <title>Accessing Nightly Builds</title>

        <para>
            Yocto Project maintains an area for nightly builds that contains
            tarball releases at <ulink url='&YOCTO_AB_NIGHTLY_URL;'/>.
            These builds include Yocto Project releases, SDK installation
            scripts, and experimental builds.
        </para>

        <para>
            Should you ever want to access a nightly build of a particular
            Yocto Project component, use the following procedure:
            <orderedlist>
                <listitem><para>
                    <emphasis>Access the Nightly Builds:</emphasis>
                    Open a browser and go to
                    <ulink url='&YOCTO_AB_NIGHTLY_URL;'/> to access the
                    Nightly Builds.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Select a Build:</emphasis>
                    Click on any build by date in which you are interested.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Find the Tarball:</emphasis>
                    Drill down to find the associated tarball.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Download the Tarball:</emphasis>
                    Click the tarball to download and save a snapshot of the
                    given component.
                    </para></listitem>
            </orderedlist>
        </para>
    </section>

    <section id='cloning-the-poky-repository'>
        <title>Cloning the <filename>poky</filename> Repository</title>

        <para>
            To use the Yocto Project, you need a release of the Yocto Project
            locally installed on your development system.
            The locally installed set of files is referred to as the
            <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
            in the Yocto Project documentation.
        </para>

        <para>
            You create your Source Directory by using
            <ulink url='&YOCTO_DOCS_GS_URL;#git'>Git</ulink> to clone a local
            copy of the upstream <filename>poky</filename> repository.
            <note><title>Tip</title>
                The preferred method of getting the Yocto Project Source
                Directory set up is to clone the repository.
            </note>
            Working from a copy of the upstream repository allows you
            to contribute back into the Yocto Project or simply work with
            the latest software on a development branch.
            Because Git maintains and creates an upstream repository with
            a complete history of changes and you are working with a local
            clone of that repository, you have access to all the Yocto
            Project development branches and tag names used in the upstream
            repository.
        </para>

        <para>
            Follow these steps to create a local version of the
            upstream
            <ulink url='&YOCTO_DOCS_REF_URL;#poky'><filename>poky</filename></ulink>
            Git repository.
            <orderedlist>
                <listitem><para>
                    <emphasis>Set Your Directory:</emphasis>
                    Be in the directory where you want to create your local
                    copy of poky.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Clone the Repository:</emphasis>
                    The following command clones the repository and uses
                    the default name "poky" for your local repository:
                    <literallayout class='monospaced'>
     $ git clone git://git.yoctoproject.org/poky
     Cloning into 'poky'...
     remote: Counting objects: 367178, done.
     remote: Compressing objects: 100% (88161/88161), done.
     remote: Total 367178 (delta 272761), reused 366942 (delta 272525)
     Receiving objects: 100% (367178/367178), 133.26 MiB | 6.40 MiB/s, done.
     Resolving deltas: 100% (272761/272761), done.
     Checking connectivity... done.
                    </literallayout>
                    Unless you specify a specific development branch or
                    tag name, Git clones the "master" branch, which results
                    in a snapshot of the latest development changes for
                    "master".
                    For information on how to check out a specific
                    development branch or on how to check out a local
                    branch based on a tag name, see the
                    "<link linkend='checking-out-by-branch-in-poky'>Checking Out By Branch in Poky</link>"
                    and
                    <link linkend='checkout-out-by-tag-in-poky'>Checking Out By Tag in Poky</link>",
                    respectively.</para>

                    <para>Once the repository is created, you can change to
                    that directory and check its status.
                    Here, the single "master" branch exists on your system
                    and by default, it is checked out:
                    <literallayout class='monospaced'>
     $ cd ~/poky
     $ git status
     On branch master
     Your branch is up-to-date with 'origin/master'.
     nothing to commit, working directory clean
     $ git branch
     * master
                    </literallayout>
                    Your local repository of poky is identical to the
                    upstream poky repository at the time from which it was
                    cloned.
                    </para></listitem>
            </orderedlist>
        </para>
    </section>

    <section id='checking-out-by-branch-in-poky'>
        <title>Checking Out by Branch in Poky</title>

        <para>
            When you clone the upstream poky repository, you have access to
            all its development branches.
            Each development branch in a repository is unique as it forks
            off the "master" branch.
            To see and use the files of a particular development branch
            locally, you need to know the branch name and then specifically
            check out that development branch.
            <note>
                Checking out an active development branch by branch name
                gives you a snapshot of that particular branch at the time
                you check it out.
                Further development on top of the branch that occurs after
                check it out can occur.
            </note>
            <orderedlist>
                <listitem><para>
                    <emphasis>Switch to the Poky Directory:</emphasis>
                    If you have a local poky Git repository, switch to that
                    directory.
                    If you do not have the local copy of poky, see the
                    "<link linkend='cloning-the-poky-repository'>Cloning the <filename>poky</filename> Repository</link>"
                    section.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Determine Existing Branch Names:</emphasis>
                    <literallayout class='monospaced'>
     $ git branch -a
     * master
       remotes/origin/1.1_M1
       remotes/origin/1.1_M2
       remotes/origin/1.1_M3
       remotes/origin/1.1_M4
       remotes/origin/1.2_M1
       remotes/origin/1.2_M2
       remotes/origin/1.2_M3
           .
           .
           .
       remotes/origin/master-next
       remotes/origin/master-next2
       remotes/origin/morty
       remotes/origin/pinky
       remotes/origin/purple
       remotes/origin/pyro
       remotes/origin/rocko
                    </literallayout>
                    </para></listitem>
                <listitem><para>
                    <emphasis>Checkout the Branch:</emphasis>
                    Checkout the development branch in which you want to work.
                    For example, to access the files for the Yocto Project
                    &DISTRO; Release (&DISTRO_NAME;), use the following command:
                    <literallayout class='monospaced'>
     $ git checkout -b &DISTRO_NAME_NO_CAP; origin/&DISTRO_NAME_NO_CAP;
     Branch &DISTRO_NAME_NO_CAP; set up to track remote branch &DISTRO_NAME_NO_CAP; from origin.
     Switched to a new branch '&DISTRO_NAME_NO_CAP;'
                    </literallayout>
                    The previous command checks out the "&DISTRO_NAME_NO_CAP;"
                    development branch and reports that the branch is tracking
                    the upstream "origin/&DISTRO_NAME_NO_CAP;" branch.</para>

                    <para>The following command displays the branches
                    that are now part of your local poky repository.
                    The asterisk character indicates the branch that is
                    currently checked out for work:
                    <literallayout class='monospaced'>
     $ git branch
       master
     * &DISTRO_NAME_NO_CAP;
                    </literallayout>
                    </para></listitem>
            </orderedlist>
        </para>
    </section>

    <section id='checkout-out-by-tag-in-poky'>
        <title>Checking Out by Tag in Poky</title>

        <para>
            Similar to branches, the upstream repository uses tags
            to mark specific commits associated with significant points in
            a development branch (i.e. a release point or stage of a
            release).
            You might want to set up a local branch based on one of those
            points in the repository.
            The process is similar to checking out by branch name except you
            use tag names.
            <note>
                Checking out a branch based on a tag gives you a
                stable set of files not affected by development on the
                branch above the tag.
            </note>
            <orderedlist>
                <listitem><para>
                    <emphasis>Switch to the Poky Directory:</emphasis>
                    If you have a local poky Git repository, switch to that
                    directory.
                    If you do not have the local copy of poky, see the
                    "<link linkend='cloning-the-poky-repository'>Cloning the <filename>poky</filename> Repository</link>"
                    section.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Fetch the Tag Names:</emphasis>
                    To checkout the branch based on a tag name, you need to
                    fetch the upstream tags into your local repository:
                    <literallayout class='monospaced'>
     $ git fetch --tags
     $
                    </literallayout>
                    </para></listitem>
                <listitem><para>
                    <emphasis>List the Tag Names:</emphasis>
                    You can list the tag names now:
                    <literallayout class='monospaced'>
     $ git tag
     1.1_M1.final
     1.1_M1.rc1
     1.1_M1.rc2
     1.1_M2.final
     1.1_M2.rc1
        .
        .
        .
     yocto-2.2
     yocto-2.2.1
     yocto-2.3
     yocto-2.3.1
     yocto-2.4
     yocto_1.5_M5.rc8
                    </literallayout>
                    </para></listitem>
                <listitem><para>
                    <emphasis>Checkout the Branch:</emphasis>
                    <literallayout class='monospaced'>
     $ git checkout tags/&DISTRO; -b my_yocto_&DISTRO;
     Switched to a new branch 'my_yocto_&DISTRO;'
     $ git branch
       master
     * my_yocto_&DISTRO;
                    </literallayout>
                    The previous command creates and checks out a local
                    branch named "my_yocto_&DISTRO;", which is based on
                    the commit in the upstream poky repository that has
                    the same tag.
                    In this example, the files you have available locally
                    as a result of the <filename>checkout</filename>
                    command are a snapshot of the
                    "&DISTRO_NAME_NO_CAP;" development branch at the point
                    where Yocto Project &DISTRO; was released.
                    </para></listitem>
            </orderedlist>
        </para>
    </section>
</section>

<section id='dev-building-an-image'>
    <title>Building an Image</title>

    <para>
        In the development environment, you need to build an image whenever
        you change hardware support, add or change system libraries, or add
        or change services that have dependencies.
        Several methods exist that allow you to build an image within the
        Yocto Project.
        This section shows you how to build an image using BitBake from a
        Linux host.
        <note><title>Notes</title>
            <itemizedlist>
                <listitem><para>
                    For information on how to build an image using
                    <ulink url='&YOCTO_DOCS_REF_URL;#toaster-term'>Toaster</ulink>,
                    see the
                    <ulink url='&YOCTO_DOCS_TOAST_URL;'>Toaster Manual</ulink>.
                    </para></listitem>
                <listitem><para>
                    For information on how to use
                    <filename>devtool</filename> to build images, see the
                    "<ulink url='&YOCTO_DOCS_SDK_URL;#using-devtool-in-your-sdk-workflow'>Using <filename>devtool</filename> in Your SDK Workflow</ulink>"
                    section in the Yocto Project Application Development and
                    the Extensible Software Development Kit (eSDK) manual.
                    </para></listitem>
                <listitem><para>
                    For a practical example on how to build an image using the
                    OpenEmbedded build system, see the
                    "<ulink url='&YOCTO_DOCS_QS_URL;#qs-building-images'>Building Images</ulink>"
                    section of the Yocto Project Quick Start.
                    </para></listitem>
            </itemizedlist>
        </note>
    </para>

    <para>
        The build process creates an entire Linux distribution from source
        and places it in your
        <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>
        under <filename>tmp/deploy/images</filename>.
        For detailed information on the build process using BitBake, see the
        "<ulink url='&YOCTO_DOCS_GS_URL;#images-dev-environment'>Images</ulink>"
        section in the Yocto Project Overview Manual.
    </para>

    <para>
        The following figure and list overviews the build process:
        <imagedata fileref="figures/bitbake-build-flow.png" width="7in" depth="4in" align="center" scalefit="1" />
        <orderedlist>
            <listitem><para>
                <emphasis>Set up Your Host Development System to Support
                Development Using the Yocto Project</emphasis>:
                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 for options on how
                to get a build host ready to use the Yocto Project.
                </para></listitem>
            <listitem><para>
                <emphasis>Initialize the Build Environment:</emphasis>
                Initialize the build environment by sourcing the build
                environment script (i.e.
                <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>):
                <literallayout class='monospaced'>
     $ source &OE_INIT_FILE; [<replaceable>build_dir</replaceable>]
                </literallayout></para>

                <para>When you use the initialization script, the
                OpenEmbedded build system uses <filename>build</filename> as
                the default Build Directory in your current work directory.
                You can use a <replaceable>build_dir</replaceable> argument
                with the script to specify a different build directory.
                <note><title>Tip</title>
                    A common practice is to use a different Build Directory for
                    different targets.
                    For example, <filename>~/build/x86</filename> for a
                    <filename>qemux86</filename> target, and
                    <filename>~/build/arm</filename> for a
                    <filename>qemuarm</filename> target.
                </note>
                </para></listitem>
            <listitem><para>
                <emphasis>Make Sure Your <filename>local.conf</filename>
                File is Correct:</emphasis>
                Ensure the <filename>conf/local.conf</filename> configuration
                file, which is found in the Build Directory,
                is set up how you want it.
                This file defines many aspects of the build environment
                including the target machine architecture through the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'>MACHINE</ulink></filename> variable,
                the packaging format used during the build
                (<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_CLASSES'><filename>PACKAGE_CLASSES</filename></ulink>),
                and a centralized tarball download directory through the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-DL_DIR'><filename>DL_DIR</filename></ulink> variable.
                </para></listitem>
            <listitem><para>
                <emphasis>Build the Image:</emphasis>
                Build the image using the <filename>bitbake</filename> command:
                <literallayout class='monospaced'>
     $ bitbake <replaceable>target</replaceable>
                </literallayout>
                <note>
                    For information on BitBake, see the
                    <ulink url='&YOCTO_DOCS_BB_URL;'>BitBake User Manual</ulink>.
                </note>
                The <replaceable>target</replaceable> is the name of the
                recipe you want to build.
                Common targets are the images in
                <filename>meta/recipes-core/images</filename>,
                <filename>meta/recipes-sato/images</filename>, etc. all found
                in the
                <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>.
                Or, the target can be the name of a recipe for a specific
                piece of software such as BusyBox.
                For more details about the images the OpenEmbedded build
                system supports, see the
                "<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>"
                chapter in the Yocto Project Reference Manual.</para>

                <para>As an example, the following command builds the
                <filename>core-image-minimal</filename> image:
                <literallayout class='monospaced'>
     $ bitbake core-image-minimal
                </literallayout>
                Once an image has been built, it often needs to be installed.
                The images and kernels built by the OpenEmbedded build system
                are placed in the Build Directory in
                <filename class="directory">tmp/deploy/images</filename>.
                For information on how to run pre-built images such as
                <filename>qemux86</filename> and <filename>qemuarm</filename>,
                see the
                <ulink url='&YOCTO_DOCS_SDK_URL;'>Yocto Project Application Development and the Extensible Software Development Kit (eSDK)</ulink>
                manual.
                For information about how to install these images, see the
                documentation for your particular board or machine.
                </para></listitem>
        </orderedlist>
    </para>
</section>

<section id='speeding-up-the-build'>
    <title>Speeding Up the Build</title>

    <para>
        Build time can be an issue.
        By default, the build system uses simple controls to try and maximize
        build efficiency.
        In general, the default settings for all the following variables
        result in the most efficient build times when dealing with single
        socket systems (i.e. a single CPU).
        If you have multiple CPUs, you might try increasing the default
        values to gain more speed.
        See the descriptions in the glossary for each variable for more
        information:
        <itemizedlist>
            <listitem><para>
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BB_NUMBER_THREADS'><filename>BB_NUMBER_THREADS</filename>:</ulink>
                The maximum number of threads BitBake simultaneously executes.
                </para></listitem>
            <listitem><para>
                <ulink url='&YOCTO_DOCS_BB_URL;#var-BB_NUMBER_PARSE_THREADS'><filename>BB_NUMBER_PARSE_THREADS</filename>:</ulink>
                The number of threads BitBake uses during parsing.
                </para></listitem>
            <listitem><para>
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PARALLEL_MAKE'><filename>PARALLEL_MAKE</filename>:</ulink>
                Extra options passed to the <filename>make</filename> command
                during the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-compile'><filename>do_compile</filename></ulink>
                task in order to specify parallel compilation on the
                local build host.
                </para></listitem>
            <listitem><para>
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PARALLEL_MAKEINST'><filename>PARALLEL_MAKEINST</filename>:</ulink>
                Extra options passed to the <filename>make</filename> command
                during the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink>
                task in order to specify parallel installation on the
                local build host.
                </para></listitem>
        </itemizedlist>
        As mentioned, these variables all scale to the number of processor
        cores available on the build system.
        For single socket systems, this auto-scaling ensures that the build
        system fundamentally takes advantage of potential parallel operations
        during the build based on the build machine's capabilities.
    </para>

    <para>
        Following are additional factors that can affect build speed:
        <itemizedlist>
            <listitem><para>
                File system type:
                The file system type that the build is being performed on can
                also influence performance.
                Using <filename>ext4</filename> is recommended as compared
                to <filename>ext2</filename> and <filename>ext3</filename>
                due to <filename>ext4</filename> improved features
                such as extents.
                </para></listitem>
            <listitem><para>
                Disabling the updating of access time using
                <filename>noatime</filename>:
                The <filename>noatime</filename> mount option prevents the
                build system from updating file and directory access times.
                </para></listitem>
            <listitem><para>
                Setting a longer commit:
                Using the "commit=" mount option increases the interval
                in seconds between disk cache writes.
                Changing this interval from the five second default to
                something longer increases the risk of data loss but decreases
                the need to write to the disk, thus increasing the build
                performance.
                </para></listitem>
            <listitem><para>
                Choosing the packaging backend:
                Of the available packaging backends, IPK is the fastest.
                Additionally, selecting a singular packaging backend also
                helps.
                </para></listitem>
            <listitem><para>
                Using <filename>tmpfs</filename> for
                <ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>
                as a temporary file system:
                While this can help speed up the build, the benefits are
                limited due to the compiler using
                <filename>-pipe</filename>.
                The build system goes to some lengths to avoid
                <filename>sync()</filename> calls into the
                file system on the principle that if there was a significant
                failure, the
                <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>
                contents could easily be rebuilt.
                </para></listitem>
            <listitem><para>
                Inheriting the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-rm-work'><filename>rm_work</filename></ulink>
                class:
                Inheriting this class has shown to speed up builds due to
                significantly lower amounts of data stored in the data
                cache as well as on disk.
                Inheriting this class also makes cleanup of
                <ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>
                faster, at the expense of being easily able to dive into the
                source code.
                File system maintainers have recommended that the fastest way
                to clean up large numbers of files is to reformat partitions
                rather than delete files due to the linear nature of
                partitions.
                This, of course, assumes you structure the disk partitions and
                file systems in a way that this is practical.
                </para></listitem>
        </itemizedlist>
        Aside from the previous list, you should keep some trade offs in
        mind that can help you speed up the build:
        <itemizedlist>
            <listitem><para>
                Remove items from
                <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></ulink>
                that you might not need.
                </para></listitem>
            <listitem><para>
                Exclude debug symbols and other debug information:
                If you do not need these symbols and other debug information,
                disabling the <filename>*-dbg</filename> package generation
                can speed up the build.
                You can disable this generation by setting the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-INHIBIT_PACKAGE_DEBUG_SPLIT'><filename>INHIBIT_PACKAGE_DEBUG_SPLIT</filename></ulink>
                variable to "1".
                </para></listitem>
            <listitem><para>
                Disable static library generation for recipes derived from
                <filename>autoconf</filename> or <filename>libtool</filename>:
                Following is an example showing how to disable static
                libraries and still provide an override to handle exceptions:
                <literallayout class='monospaced'>
     STATICLIBCONF = "--disable-static"
     STATICLIBCONF_sqlite3-native = ""
     EXTRA_OECONF += "${STATICLIBCONF}"
                </literallayout>
                <note><title>Notes</title>
                    <itemizedlist>
                        <listitem><para>
                            Some recipes need static libraries in order to work
                            correctly (e.g. <filename>pseudo-native</filename>
                            needs <filename>sqlite3-native</filename>).
                            Overrides, as in the previous example, account for
                            these kinds of exceptions.
                            </para></listitem>
                        <listitem><para>
                            Some packages have packaging code that assumes the
                            presence of the static libraries.
                            If so, you might need to exclude them as well.
                            </para></listitem>
                    </itemizedlist>
                </note>
            </para></listitem>
        </itemizedlist>
    </para>
</section>
</chapter>
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