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

<title>Setting Up to Use the Yocto Project</title>

<para>
    This chapter provides procedures related to getting set up to use the
    Yocto Project.
    You can learn about creating a team environment that develops using the
    Yocto Project, how to set up a build host, how to locate Yocto Project
    source repositories, and how to create local Git repositories.
</para>

<section id="usingpoky-changes-collaborate">
    <title>Creating a Team Development Environment</title>

    <para>
        It might not be immediately clear how you can use the Yocto
        Project in a team development environment, or scale it for a large
        team of developers.
        One of the strengths of the Yocto Project is that it is extremely
        flexible.
        Thus, you can adapt it to many different use cases and scenarios.
        However, these characteristics can cause a struggle if you are trying
        to create a working setup that scales across a large team.
    </para>

    <para>
        To help you understand how to set up this type of environment,
        this section presents a procedure that gives you the information
        to learn how to get the results you want.
        The procedure is high-level and presents some of the project's most
        successful experiences, practices, solutions, and available
        technologies that work well.
        Keep in mind, the procedure here is a starting point.
        You can build off it and customize it to fit any
        particular working environment and set of practices.
        <orderedlist>
            <listitem><para>
                <emphasis>Determine Who is Going to be Developing:</emphasis>
                You need to understand who is going to be doing anything
                related to the Yocto Project and what their roles would be.
                Making this determination is essential to completing the
                steps two and three, which are to get your equipment together
                and set up your development environment's hardware topology.
                </para>

                <para>The following roles exist:
                <itemizedlist>
                    <listitem><para>
                        <emphasis>Application Development:</emphasis>
                        These types of developers do application level work
                        on top of an existing software stack.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Core System Development:</emphasis>
                        These types of developers work on the contents of the
                        operating system image itself.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Build Engineer:</emphasis>
                        This type of developer manages Autobuilders and
                        releases.
                        Not all environments need a Build Engineer.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Test Engineer:</emphasis>
                        This type of developer creates and manages automated
                        tests needed to ensure all application and core
                        system development meets desired quality standards.
                        </para></listitem>
                </itemizedlist>
                </para></listitem>
            <listitem><para>
                <emphasis>Gather the Hardware:</emphasis>
                Based on the size and make-up of the team, get the hardware
                together.
                Any development, build, or test engineer should be using
                a system that is running a supported Linux distribution.
                Systems, in general, should be high performance (e.g. dual,
                six-core Xeons with 24 Gbytes of RAM and plenty of disk space).
                You can help ensure efficiency by having any machines used
                for testing or that run Autobuilders be as high performance
                as possible.
                </para></listitem>
            <listitem><para>
                <emphasis>Understand the Hardware Topology of the Environment:</emphasis>
                Once you understand the hardware involved and the make-up
                of the team, you can understand the hardware topology of the
                development environment.
                You can get a visual idea of the machines and their roles
                across the development environment.

<!--
                The following figure shows a moderately sized Yocto Project
                development environment.

                <para role="writernotes">
                Need figure.</para>
-->

                </para></listitem>
            <listitem><para>
                <emphasis>Use Git as Your Source Control Manager (SCM):</emphasis>
                Keeping your
                <ulink url='&YOCTO_DOCS_REF_URL;#metadata'>Metadata</ulink>
                and any software you are developing under the
                control of an SCM system that is compatible
                with the OpenEmbedded build system is advisable.
                Of the SCMs BitBake supports, the
                Yocto Project team strongly recommends using
                <ulink url='&YOCTO_DOCS_OM_URL;#git'>Git</ulink>.
                Git is a distributed system that is easy to backup,
                allows you to work remotely, and then connects back to the
                infrastructure.
                <note>
                    For information about BitBake, see the
                    <ulink url='&YOCTO_DOCS_BB_URL;'>BitBake User Manual</ulink>.
                </note></para>

                <para>It is relatively easy to set up Git services and create
                infrastructure like
                <ulink url='&YOCTO_GIT_URL;'>http://git.yoctoproject.org</ulink>,
                which is based on server software called
                <filename>gitolite</filename> with <filename>cgit</filename>
                being used to generate the web interface that lets you view the
                repositories.
                The <filename>gitolite</filename> software identifies users
                using SSH keys and allows branch-based
                access controls to repositories that you can control as little
                or as much as necessary.

                <note>
                   The setup of these services is beyond the scope of this
                   manual.
                   However, sites such as these exist that describe how to
                   perform setup:
                   <itemizedlist>
                       <listitem><para>
                           <ulink url='http://git-scm.com/book/ch4-8.html'>Git documentation</ulink>:
                           Describes how to install <filename>gitolite</filename>
                           on the server.
                           </para></listitem>
                       <listitem><para>
                           <ulink url='http://gitolite.com'>Gitolite</ulink>:
                            Information for <filename>gitolite</filename>.
                            </para></listitem>
                        <listitem><para>
                            <ulink url='https://git.wiki.kernel.org/index.php/Interfaces,_frontends,_and_tools'>Interfaces, frontends, and tools</ulink>:
                            Documentation on how to create interfaces and frontends
                            for Git.
                            </para></listitem>
                    </itemizedlist>
                </note>
                </para></listitem>
            <listitem><para>
                <emphasis>Set up the Application Development Machines:</emphasis>
                As mentioned earlier, application developers are creating
                applications on top of existing software stacks.
                Following are some best practices for setting up machines
                that do application development:
                <itemizedlist>
                    <listitem><para>
                        Use a pre-built toolchain that
                        contains the software stack itself.
                        Then, develop the application code on top of the
                        stack.
                        This method works well for small numbers of relatively
                        isolated applications.
                        </para></listitem>
                    <listitem><para>
                        When possible, use the Yocto Project
                        plug-in for the
                        <trademark class='trade'>Eclipse</trademark> IDE
                        and SDK development practices.
                        For more information, see the
                        "<ulink url='&YOCTO_DOCS_SDK_URL;'>Yocto Project Application Development and the Extensible Software Development Kit (eSDK)</ulink>"
                        manual.
                        </para></listitem>
                    <listitem><para>
                        Keep your cross-development toolchains updated.
                        You can do this through provisioning either as new
                        toolchain downloads or as updates through a package
                        update mechanism using <filename>opkg</filename>
                        to provide updates to an existing toolchain.
                        The exact mechanics of how and when to do this are a
                        question for local policy.
                        </para></listitem>
                    <listitem><para>
                        Use multiple toolchains installed locally
                        into different locations to allow development across
                        versions.
                        </para></listitem>
                </itemizedlist>
                </para></listitem>
            <listitem><para>
                <emphasis>Set up the Core Development Machines:</emphasis>
                As mentioned earlier, these types of developers work on the
                contents of the operating system itself.
                Following are some best practices for setting up machines
                used for developing images:
                <itemizedlist>
                    <listitem><para>
                        Have the Yocto Project build system itself available on
                        the developer workstations so developers can run their own
                        builds and directly rebuild the software stack.
                        </para></listitem>
                    <listitem><para>
                        Keep the core system unchanged as much as
                        possible and do your work in layers on top of the
                        core system.
                        Doing so gives you a greater level of portability when
                        upgrading to new versions of the core system or Board
                        Support Packages (BSPs).
                        </para></listitem>
                    <listitem><para>
                        Share layers amongst the developers of a
                        particular project and contain the policy configuration
                        that defines the project.
                        </para></listitem>
                </itemizedlist>
                </para></listitem>
            <listitem><para>
                <emphasis>Set up an Autobuilder:</emphasis>
                Autobuilders are often the core of the development
                environment.
                It is here that changes from individual developers are brought
                together and centrally tested and subsequent decisions about
                releases can be made.
                Autobuilders also allow for "continuous integration" style
                testing of software components and regression identification
                and tracking.</para>

                <para>See "<ulink url='http://autobuilder.yoctoproject.org'>Yocto Project Autobuilder</ulink>"
                for more information and links to buildbot.
                The Yocto Project team has found this implementation
                works well in this role.
                A public example of this is the Yocto Project
                Autobuilders, which we use to test the overall health of the
                project.</para>

                <para>The features of this system are:
                <itemizedlist>
                    <listitem><para>
                         Highlights when commits break the build.
                         </para></listitem>
                    <listitem><para>
                        Populates an sstate cache from which
                        developers can pull rather than requiring local
                        builds.
                        </para></listitem>
                    <listitem><para>
                        Allows commit hook triggers,
                        which trigger builds when commits are made.
                        </para></listitem>
                    <listitem><para>
                        Allows triggering of automated image booting
                        and testing under the QuickEMUlator (QEMU).
                        </para></listitem>
                    <listitem><para>
                        Supports incremental build testing and
                        from-scratch builds.
                        </para></listitem>
                    <listitem><para>
                        Shares output that allows developer
                        testing and historical regression investigation.
                        </para></listitem>
                    <listitem><para>
                        Creates output that can be used for releases.
                        </para></listitem>
                    <listitem><para>
                        Allows scheduling of builds so that resources
                        can be used efficiently.
                        </para></listitem>
               </itemizedlist>
               </para></listitem>
           <listitem><para>
               <emphasis>Set up Test Machines:</emphasis>
               Use a small number of shared, high performance systems
               for testing purposes.
               Developers can use these systems for wider, more
               extensive testing while they continue to develop
               locally using their primary development system.
               </para></listitem>
           <listitem><para>
               <emphasis>Document Policies and Change Flow:</emphasis>
               The Yocto Project itself uses a hierarchical structure and a
                pull model.
                Scripts exist to create and send pull requests
                (i.e. <filename>create-pull-request</filename> and
                <filename>send-pull-request</filename>).
                This model is in line with other open source projects where
                maintainers are responsible for specific areas of the project
                and a single maintainer handles the final "top-of-tree" merges.
                <note>
                    You can also use a more collective push model.
                    The <filename>gitolite</filename> software supports both the
                    push and pull models quite easily.
                </note></para>

                <para>As with any development environment, it is important
                to document the policy used as well as any main project
                guidelines so they are understood by everyone.
                It is also a good idea to have well structured
                commit messages, which are usually a part of a project's
                guidelines.
                Good commit messages are essential when looking back in time and
                trying to understand why changes were made.</para>

                <para>If you discover that changes are needed to the core
                layer of the project, it is worth sharing those with the
                community as soon as possible.
                Chances are if you have discovered the need for changes,
                someone else in the community needs them also.
                </para></listitem>
            <listitem><para>
                <emphasis>Development Environment Summary:</emphasis>
                Aside from the previous steps, some best practices exist
                within the Yocto Project development environment.
                Consider the following:
                <itemizedlist>
                    <listitem><para>
                        Use
                        <ulink url='&YOCTO_DOCS_OM_URL;#git'>Git</ulink>
                        as the source control system.
                        </para></listitem>
                    <listitem><para>
                        Maintain your Metadata in layers that make sense
                        for your situation.
                        See the "<link linkend='understanding-and-creating-layers'>Understanding
                        and Creating Layers</link>" section for more information on
                        layers.
                        </para></listitem>
                    <listitem><para>
                        Separate the project's Metadata and code by using
                        separate Git repositories.
                        See the
                        "<ulink url='&YOCTO_DOCS_OM_URL;#yocto-project-repositories'>Yocto Project Source Repositories</ulink>"
                        section for information on these repositories.
                        See the
                        "<link linkend='locating-yocto-project-source-files'>Locating Yocto Project Source Files</link>"
                        section for information on how to set up local Git
                        repositories for related upstream Yocto Project
                        Git repositories.
                        </para></listitem>
                    <listitem><para>
                        Set up the directory for the shared state cache
                        (<ulink url='&YOCTO_DOCS_REF_URL;#var-SSTATE_DIR'><filename>SSTATE_DIR</filename></ulink>)
                        where it makes sense.
                        For example, set up the sstate cache on a system used
                        by developers in the same organization and share the
                        same source directories on their machines.
                        </para></listitem>
                    <listitem><para>
                        Set up an Autobuilder and have it populate the
                        sstate cache and source directories.
                        </para></listitem>
                    <listitem><para>
                        The Yocto Project community encourages you
                        to send patches to the project to fix bugs or add features.
                        If you do submit patches, follow the project commit
                        guidelines for writing good commit messages.
                        See the "<link linkend='how-to-submit-a-change'>Submitting a Change to the Yocto Project</link>"
                        section.
                        </para></listitem>
                    <listitem><para>
                        Send changes to the core sooner than later
                        as others are likely to run into the same issues.
                        For some guidance on mailing lists to use, see the list in the
                        "<link linkend='how-to-submit-a-change'>Submitting a Change to the Yocto Project</link>"
                        section.
                        For a description of the available mailing lists, see the
                        "<ulink url='&YOCTO_DOCS_REF_URL;#resources-mailinglist'>Mailing Lists</ulink>"
                        section in the Yocto Project Reference Manual.
                        </para></listitem>
                </itemizedlist>
                </para></listitem>
        </orderedlist>
    </para>
</section>

<section id='setting-up-the-development-host-to-use-the-yocto-project'>
    <title>Preparing the Build Host</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 to 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 Docker:</emphasis>
                    If you are unfamiliar with Docker 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='locating-yocto-project-source-files'>
    <title>Locating Yocto Project Source Files</title>

    <para>
        This section contains procedures related to locating 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_OM_URL;#git'>Git</ulink>"
                    section in the Yocto Project Overview and Concepts Manual.
                    </para></listitem>
                <listitem><para>
                    For concepts on Yocto Project source repositories, see the
                    "<ulink url='&YOCTO_DOCS_OM_URL;#yocto-project-repositories'>Yocto Project Source Repositories</ulink>"
                    section in the Yocto Project Overview and Concepts 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_OM_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;'></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_OM_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" page 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>
                    Select the "DOWNLOADS" item from the pull-down
                    "SOFTWARE" tab menu.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Select a Yocto Project Release:</emphasis>
                    Use the menu next to "RELEASE" to display and choose
                    a Yocto Project release (e.g. sumo, rocko, pyro, and
                    so forth.
                    For a "map" of Yocto Project releases to version numbers,
                    see the
                    <ulink url='https://wiki.yoctoproject.org/wiki/Releases'>Releases</ulink>
                    wiki page.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Download Tools or Board Support Packages (BSPs):</emphasis>
                    From the "DOWNLOADS" page, you can download tools or
                    BSPs as well.
                    Just scroll down the page and look for what you need.
                    </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>

<section id='cloning-and-checking-out-branchs'>
    <title>Cloning and Checking Out Branches</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_OM_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>

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

        <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>"
                    sections, 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_REL_TAG; -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='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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