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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title></title><link rel="stylesheet" href="mega-style.css" type="text/css" /><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /></head><body><div xml:lang="en" class="book" lang="en"><div class="titlepage"><hr /></div>

    <div class="article"><div class="titlepage"><hr /></div><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="540"><tr style="height: 90px"><td align="right"><img src="figures/yocto-project-transp.png" align="right" width="135" /></td></tr></table><div class="section" title="1. The Yocto Project Quick Start"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="fake-title"></a>1. The Yocto Project Quick Start</h2></div></div></div><p>Copyright © 2010-2012 Linux Foundation</p></div><div class="section" title="2. Welcome!"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="welcome"></a>2. Welcome!</h2></div></div></div><p>
        Welcome to the Yocto Project!  
        The Yocto Project is an open-source collaboration project focused on embedded Linux
        developers.
        Among other things, the Yocto Project uses a build system based on the Poky project
        to construct complete Linux images.
        The Poky project, in turn, draws from and contributes back to the OpenEmbedded project.
    </p><p>
        If you don't have a system that runs Linux and you want to give the Yocto Project a test run, 
        you might consider using the Yocto Project Build Appliance.
        The Build Appliance allows you to build and boot a custom embedded Linux image with the Yocto 
        Project using a non-Linux development system.  
        See the <a class="ulink" href="http://www.yoctoproject.org/documentation/build-appliance" target="_top">Yocto 
        Project Build Appliance</a> for more information.
    </p><p>
        On the other hand, if you know all about open-source development, Linux development environments, 
        Git source repositories and the like and you just want some quick information that lets you try out
        the Yocto Project on your Linux system, skip right to the 
        "<a class="link" href="#super-user" title="6. Super User">Super User</a>" section at the end of this quick start.
    </p><p>
        For the rest of you, this short document will give you some basic information about the environment and 
        let you experience it in its simplest form.  
        After reading this document, you will have a basic understanding of what the Yocto Project is
        and how to use some of its core components.  
        This document steps you through a simple example showing you how to build a small image 
        and run it using the Quick EMUlator (QEMU emulator).
    </p><p>
        For more detailed information on the Yocto Project, you should check out these resources:
        </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><span class="emphasis"><em>Website:</em></span> The <a class="ulink" href="http://www.yoctoproject.org" target="_top">Yocto Project Website</a>
                provides the latest builds, breaking news, full development documentation, and a rich Yocto 
                Project Development Community into which you can tap.
                </p></li><li class="listitem"><p><span class="emphasis"><em>FAQs:</em></span> Lists commonly asked Yocto Project questions and answers.
                You can find two FAQs: <a class="ulink" href="https://wiki.yoctoproject.org/wiki/FAQ" target="_top">Yocto Project FAQ</a> on 
                a wiki, and the 
                <a class="link" href="#faq" target="_top">FAQ</a> chapter in  
                the Yocto Project Reference Manual.
                </p></li><li class="listitem"><p><span class="emphasis"><em>Developer Screencast:</em></span> The 
                <a class="ulink" href="http://vimeo.com/36450321" target="_top">Getting Started with the Yocto Project - New
                Developer Screencast Tutorial</a> provides a 30-minute video for the user 
                new to the Yocto Project but familiar with Linux build systems.</p></li></ul></div><p>
    </p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
        Due to production processes, there could be differences between the Yocto Project
        documentation bundled in a released tarball and the 
        Yocto Project Quick Start on
        the <a class="ulink" href="http://www.yoctoproject.org" target="_top">Yocto Project</a> website.
        For the latest version of this manual, see the manual on the website.
    </div></div><div class="section" title="3. Introducing the Yocto Project Development Environment"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="yp-intro"></a>3. Introducing the Yocto Project Development Environment</h2></div></div></div><p>
        The Yocto Project through the OpenEmbedded build system provides an open source development 
        environment targeting the ARM, MIPS, PowerPC and x86 architectures for a variety of 
        platforms including x86-64 and emulated ones.
        You can use components from the Yocto Project to design, develop, build, debug, simulate,
        and test the complete software stack using Linux, the X Window System, GNOME Mobile-based
        application frameworks, and Qt frameworks.
    </p><div class="mediaobject" align="center"><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><img src="figures/yocto-environment.png" align="middle" width="100%" /></td></tr></table><div class="caption"><p>The Yocto Project Development Environment</p></div></div><p>
        Here are some highlights for the Yocto Project:
    </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>Provides a recent Linux kernel along with a set of system commands and libraries suitable for the embedded environment.</p></li><li class="listitem"><p>Makes available system components such as X11, Matchbox, GTK+, Pimlico, Clutter,
            GuPNP and Qt (among others) so you can create a richer user interface experience on 
            devices that use displays or have a GUI.
            For devices that don't have a GUI or display, you simply would not employ these 
            components.</p></li><li class="listitem"><p>Creates a focused and stable core compatible with the OpenEmbedded 
            project with which you can easily and reliably build and develop.</p></li><li class="listitem"><p>Fully supports a wide range of hardware and device emulation through the QEMU
            Emulator.</p></li></ul></div><p>
        The Yocto Project can generate images for many kinds of devices.  
        However, the standard example machines target QEMU full-system emulation for x86, x86-64, ARM, MIPS,
        and PPC-based architectures as well as specific hardware such as the 
        <span class="trademark">Intel</span>® Desktop Board DH55TC.  
        Because an image developed with the Yocto Project can boot inside a QEMU emulator, the 
        development environment works nicely as a test platform for developing embedded software.
    </p><p>
        Another important Yocto Project feature is the Sato reference User Interface. 
        This optional GNOME mobile-based UI, which is intended for devices with
        restricted screen sizes, sits neatly on top of a device using the 
        GNOME Mobile Stack and provides a well-defined user experience. 
        Implemented in its own layer, it makes it clear to developers how they can implement 
        their own user interface on top of a Linux image created with the Yocto Project.
    </p></div><div class="section" title="4. What You Need and How You Get It"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="yp-resources"></a>4. What You Need and How You Get It</h2></div></div></div><p>
        You need these things to develop in the Yocto Project environment:
    </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>A host system running a supported Linux distribution (i.e. recent releases of
                Fedora, openSUSE, CentOS, and Ubuntu).
                If the host system supports multiple cores and threads, you can configure the 
                Yocto Project build system to decrease the time needed to build images
                significantly.
            </p></li><li class="listitem"><p>The right packages.</p></li><li class="listitem"><p>A release of the Yocto Project.</p></li></ul></div><div class="section" title="4.1. The Linux Distribution"><div class="titlepage"><div><div><h3 class="title"><a id="the-linux-distro"></a>4.1. The Linux Distribution</h3></div></div></div><p>
            The Yocto Project team is continually verifying more and more Linux 
            distributions with each release.
            In general, if you have the current release minus one of the following 
            distributions you should have no problems.
            </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>Ubuntu</p></li><li class="listitem"><p>Fedora</p></li><li class="listitem"><p>openSUSE</p></li><li class="listitem"><p>CentOS</p></li></ul></div><p>
            For a list of the distributions under validation and their status, see the
            <a class="ulink" href="https://wiki.yoctoproject.org/wiki/Distribution_Support" target="_top">Distribution
            Support</a> wiki page.
            </p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
                For notes about using the Yocto Project on a RHEL 4-based host, see the
                <a class="ulink" href="https://wiki.yoctoproject.org/wiki/BuildingOnRHEL4" target="_top">BuildingOnRHEL4</a>
                wiki page.
            </div><p>
            </p><p>
            The OpenEmbedded build system should be able to run on any modern distribution with Python 2.6 or 2.7.
            Earlier releases of Python are known to not work and the system does not support Python 3 at this time.
            This document assumes you are running one of the previously noted distributions on your Linux-based 
            host systems.
        </p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
            If you attempt to use a distribution not in the above list, you may or may not have success - you 
            are venturing into untested territory.
            Refer to  
            <a class="ulink" href="http://www.openembedded.org/index.php?title=OEandYourDistro&amp;action=historysubmit&amp;diff=4309&amp;okdid=4225" target="_top">OE and Your Distro</a> and 
            <a class="ulink" href="http://www.openembedded.org/index.php?title=Required_software&amp;action=historysubmit&amp;diff=4311&amp;oldid=4251" target="_top">Required Software</a> 
            for information for other distributions used with the OpenEmbedded project, which might be
            a starting point for exploration.
            If you go down this path, you should expect problems.
            When you do, please go to <a class="ulink" href="http://bugzilla.yoctoproject.org" target="_top">Yocto Project Bugzilla</a>
            and submit a bug.
            We are interested in hearing about your experience.
        </p></div></div><div class="section" title="4.2. The Packages"><div class="titlepage"><div><div><h3 class="title"><a id="packages"></a>4.2. The Packages</h3></div></div></div><p>
            Packages and package installation vary depending on your development system.  
            In general, you need to have root access and then install the required packages.
            The next few sections show you how to get set up with the right packages for
            Ubuntu, Fedora, openSUSE, and CentOS.
        </p><div class="section" title="4.2.1. Ubuntu"><div class="titlepage"><div><div><h4 class="title"><a id="ubuntu"></a>4.2.1. Ubuntu</h4></div></div></div><p>
                The packages you need for a supported Ubuntu distribution are shown in the following command:
            </p><pre class="literallayout">
     $ sudo apt-get install sed wget subversion git-core coreutils \
     unzip texi2html texinfo libsdl1.2-dev docbook-utils fop gawk \
     python-pysqlite2 diffstat make gcc build-essential xsltproc \
     g++ desktop-file-utils chrpath libgl1-mesa-dev libglu1-mesa-dev \
     autoconf automake groff libtool xterm libxml-parser-perl dblatex
                </pre></div><div class="section" title="4.2.2. Fedora"><div class="titlepage"><div><div><h4 class="title"><a id="fedora"></a>4.2.2. Fedora</h4></div></div></div><p>
                The packages you need for a supported Fedora distribution are shown in the following
                commands:
            </p><pre class="literallayout">
     $ sudo yum groupinstall "development tools"
     $ sudo yum install python m4 make wget curl ftp tar bzip2 gzip \
     unzip perl texinfo texi2html diffstat openjade \
     docbook-style-dsssl sed docbook-style-xsl docbook-dtds fop libxslt \
     docbook-utils sed bc eglibc-devel ccache pcre pcre-devel quilt \
     groff linuxdoc-tools patch cmake \
     perl-ExtUtils-MakeMaker tcl-devel gettext chrpath ncurses apr \
     SDL-devel mesa-libGL-devel mesa-libGLU-devel gnome-doc-utils \
     autoconf automake libtool xterm dblatex
                </pre></div><div class="section" title="4.2.3. openSUSE"><div class="titlepage"><div><div><h4 class="title"><a id="opensuse"></a>4.2.3. openSUSE</h4></div></div></div><p>
                The packages you need for a supported openSUSE distribution are shown in the following 
                command:
            </p><pre class="literallayout">
     $ sudo zypper install python gcc gcc-c++ libtool fop \
     subversion git chrpath automake make wget xsltproc \
     diffstat texinfo freeglut-devel libSDL-devel dblatex
                </pre></div><div class="section" title="4.2.4. CentOS"><div class="titlepage"><div><div><h4 class="title"><a id="centos"></a>4.2.4. CentOS</h4></div></div></div><p>
                The packages you need for a supported CentOS distribution are shown in the following 
                commands:
            </p><pre class="literallayout">
     $ sudo yum -y groupinstall "development tools"
     $ sudo yum -y install tetex gawk sqlite-devel vim-common redhat-lsb xz \
       m4 make wget curl ftp tar bzip2 gzip python-devel \
       unzip perl texinfo texi2html diffstat openjade zlib-devel \
       docbook-style-dsssl sed docbook-style-xsl docbook-dtds \
       docbook-utils bc glibc-devel pcre pcre-devel \
       groff linuxdoc-tools patch cmake \
       tcl-devel gettext ncurses apr \
       SDL-devel mesa-libGL-devel mesa-libGLU-devel gnome-doc-utils \
       autoconf automake libtool xterm dblatex
                </pre><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
                Depending on the CentOS version you are using, other requirements and dependencies
                might exist. 
                For details, you should look at the CentOS sections on the 
                <a class="ulink" href="https://wiki.yoctoproject.org/wiki/Poky/GettingStarted/Dependencies" target="_top">Poky/GettingStarted/Dependencies</a>
                wiki page.
            </p></div></div></div><div class="section" title="4.3. Yocto Project Release"><div class="titlepage"><div><div><h3 class="title"><a id="releases"></a>4.3. Yocto Project Release</h3></div></div></div><p>
            You can download the latest Yocto Project release by going to the 
            <a class="ulink" href="http://www.yoctoproject.org/download" target="_top">Yocto Project Download page</a>.
            Just go to the page and click the "Yocto Downloads" link found in the "Download"
            navigation pane to the right to view all available Yocto Project releases. 
            Then, click the "Yocto Release" link for the release you want from the list to 
            begin the download. 
            Nightly and developmental builds are also maintained at
            <a class="ulink" href="http://autobuilder.yoctoproject.org/nightly/" target="_top">http://autobuilder.yoctoproject.org/nightly/</a>.  
            However, for this document a released version of Yocto Project is used.
        </p><p>
            You can also get the Yocto Project files you need by setting up (cloning in Git terms)
            a local copy of the <code class="filename">poky</code> Git repository on your host development 
            system. 
            Doing so allows you to contribute back to the Yocto Project project.
            For information on how to get set up using this method, see the 
            "<a class="link" href="#local-yp-release" target="_top">Yocto 
            Project Release</a>" item in the Yocto Project Development Manual.
        </p></div></div><div class="section" title="5. A Quick Test Run"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="test-run"></a>5. A Quick Test Run</h2></div></div></div><p>
        Now that you have your system requirements in order, you can give the Yocto Project a try.  
        This section presents some steps that let you do the following:
    </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>Build an image and run it in the QEMU emulator</p></li><li class="listitem"><p>Use a pre-built image and run it in the QEMU emulator</p></li></ul></div><div class="section" title="5.1. Building an Image"><div class="titlepage"><div><div><h3 class="title"><a id="building-image"></a>5.1. Building an Image</h3></div></div></div><p>
            In the development environment you will need to build an image whenever you change hardware 
            support, add or change system libraries, or add or change services that have dependencies.
        </p><div class="mediaobject" align="center"><img src="figures/building-an-image.png" align="middle" /><div class="caption"><p>Building an Image</p></div></div><p>
             Use the following commands to build your image.  
             The OpenEmbedded build process creates an entire Linux distribution, including the toolchain, 
             from source.
         </p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
             The build process using Sato currently consumes about 50GB of disk space.
             To allow for variations in the build process and for future package expansion, we 
             recommend having at least 100GB of free disk space.
         </p></div><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
             By default, the build process searches for source code using a pre-determined order
             through a set of locations.
             If you encounter problems with the build process finding and downloading source code, see the 
             "<a class="link" href="#how-does-the-yocto-project-obtain-source-code-and-will-it-work-behind-my-firewall-or-proxy-server" target="_top">How does the OpenEmbedded build system obtain source code and will it work behind my
             firewall or proxy server?</a>" in the Yocto Project Reference Manual.
         </p></div><p>
             </p><pre class="literallayout">
     $ wget http://downloads.yoctoproject.org/releases/yocto/yocto-1.3/poky-1.2+snapshot-8.0.tar.bz2
     $ tar xjf poky-1.2+snapshot-8.0.tar.bz2
     $ source poky-1.2+snapshot-8.0/oe-init-build-env poky-1.2+snapshot-8.0-build
             </pre><p>
         </p><div class="tip" title="Tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Tip</h3><p>
             To help conserve disk space during builds, you can add the following statement
             to your project's configuration file, which for this example
             is <code class="filename">poky-1.2+snapshot-8.0-build/conf/local.conf</code>.
             Adding this statement deletes the work directory used for building a package
             once the package is built.
             </p><pre class="literallayout">
     INHERIT += "rm_work"
             </pre><p>
         </p></div><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>In the previous example, the first command retrieves the Yocto Project
                 release tarball from the source repositories using the
                 <code class="filename">wget</code> command.
                 Alternatively, you can go to the 
                 <a class="ulink" href="http://www.yoctoproject.org/download" target="_top">Yocto Project website's Downloads page</a>
                 to retrieve the tarball.</p></li><li class="listitem"><p>The second command extracts the files from the tarball and places 
                 them into a directory named <code class="filename">poky-1.2+snapshot-8.0</code> in the current 
                 directory.</p></li><li class="listitem"><p>The third command runs the Yocto Project environment setup script.
                 Running this script defines OpenEmbedded build environment settings needed to 
                 complete the build.
                 The script also creates the 
                 <a class="link" href="#build-directory" target="_top">build directory</a>,
                 which is <code class="filename">poky-1.2+snapshot-8.0-build</code> in this case.
                 After the script runs, your current working directory is set 
                 to the build directory.
                 Later, when the build completes, the build directory contains all the files 
                 created during the build.
                 </p></li></ul></div><p>
             Take some time to examine your <code class="filename">local.conf</code> file 
             in your project's configuration directory.
             The defaults in that file should work fine.
             However, there are some variables of interest at which you might look.
         </p><p>  
             By default, the target architecture for the build is <code class="filename">qemux86</code>, 
             which produces an image that can be used in the QEMU emulator and is targeted at an
             <span class="trademark">Intel</span>® 32-bit based architecture.
             To change this default, edit the value of the <code class="filename">MACHINE</code> variable 
             in the configuration file before launching the build.
         </p><p>
             Another couple of variables of interest are the 
             <a class="link" href="#var-BB_NUMBER_THREADS" target="_top"><code class="filename">BB_NUMBER_THREADS</code></a> and the 
             <a class="link" href="#var-PARALLEL_MAKE" target="_top"><code class="filename">PARALLEL_MAKE</code></a> variables.
             By default, these variables are commented out. 
             However, if you have a multi-core CPU you might want to uncomment
             the lines and set both variables equal to twice the number of your 
             host's processor cores.
             Setting these variables can significantly shorten your build time.
         </p><p>
            Another consideration before you build is the package manager used when creating 
            the image. 
            By default, the OpenEmbedded build system uses the RPM package manager.
            You can control this configuration by using the 
            <code class="filename"><a class="link" href="#var-PACKAGE_CLASSES" target="_top"><code class="filename">PACKAGE_CLASSES</code></a></code> variable.  
             For additional package manager selection information, see 
             "<a class="link" href="#ref-classes-package" target="_top">Packaging - <code class="filename">package*.bbclass</code></a>" 
             in the Yocto Project Reference Manual.
        </p><p>
             Continue with the following command to build an OS image for the target, which is 
             <code class="filename">core-image-sato</code> in this example.
             For information on the <code class="filename">-k</code> option use the 
             <code class="filename">bitbake --help</code> command or see the
             "<a class="link" href="#usingpoky-components-bitbake" target="_top">BitBake</a>" section in 
             the Yocto Project Reference Manual.
             </p><pre class="literallayout">
     $ bitbake -k core-image-sato
             </pre><p>
             </p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
                 BitBake requires Python 2.6 or 2.7.  For more information on this requirement, 
                 see the 
                 <a class="link" href="#faq" target="_top">FAQ</a> in the Yocto Project Reference 
                 Manual.
             </p></div><p>
             The final command runs the image:
             </p><pre class="literallayout">
     $ runqemu qemux86
             </pre><p>
             </p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
                 Depending on the number of processors and cores, the amount or RAM, the speed of your
                 Internet connection and other factors, the build process could take several hours the first
                 time you run it.
                 Subsequent builds run much faster since parts of the build are cached.
             </p></div><p>
         </p></div><div class="section" title="5.2. Using Pre-Built Binaries and QEMU"><div class="titlepage"><div><div><h3 class="title"><a id="using-pre-built"></a>5.2. Using Pre-Built Binaries and QEMU</h3></div></div></div><p>
            If hardware, libraries and services are stable, you can get started by using a pre-built binary 
            of the filesystem image, kernel, and toolchain and run it using the QEMU emulator.  
            This scenario is useful for developing application software.
        </p><div class="mediaobject" align="center"><img src="figures/using-a-pre-built-image.png" align="middle" /><div class="caption"><p>Using a Pre-Built Image</p></div></div><p>
            For this scenario, you need to do several things:
        </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>Install the appropriate stand-alone toolchain tarball.</p></li><li class="listitem"><p>Download the pre-built image that will boot with QEMU.  
                You need to be sure to get the QEMU image that matches your target machine’s 
                architecture (e.g. x86, ARM, etc.).</p></li><li class="listitem"><p>Download the filesystem image for your target machine's architecture.
                </p></li><li class="listitem"><p>Set up the environment to emulate the hardware and then start the QEMU emulator.
                </p></li></ul></div><div class="section" title="5.2.1. Installing the Toolchain"><div class="titlepage"><div><div><h4 class="title"><a id="installing-the-toolchain"></a>5.2.1. Installing the Toolchain</h4></div></div></div><p>
                You can download a tarball with the pre-built toolchain, which includes the 
                <code class="filename">runqemu</code> 
                script and support files, from the appropriate directory under
                <a class="ulink" href="http://downloads.yoctoproject.org/releases/yocto/yocto-1.3/toolchain/" target="_top">http://downloads.yoctoproject.org/releases/yocto/yocto-1.3/toolchain/</a>.  
                Toolchains are available for 32-bit and 64-bit development systems from the 
                <code class="filename">i686</code> and <code class="filename">x86-64</code> directories, respectively. 
                Each type of development system supports five target architectures.
                The names of the tarballs are such that a string representing the host system appears 
                first in the filename and then is immediately followed by a string representing
                the target architecture.
            </p><pre class="literallayout">
     poky-eglibc-&lt;<span class="emphasis"><em>host_system</em></span>&gt;-&lt;<span class="emphasis"><em>arch</em></span>&gt;-toolchain-gmae-&lt;<span class="emphasis"><em>release</em></span>&gt;.tar.bz2

     Where:
         &lt;<span class="emphasis"><em>host_system</em></span>&gt; is a string representing your development system: 
                i686 or x86_64.
       
         &lt;<span class="emphasis"><em>arch</em></span>&gt; is a string representing the target architecture: 
                i586, x86_64, powerpc, mips, or arm.
       
         &lt;<span class="emphasis"><em>release</em></span>&gt; is the version of Yocto Project.
            </pre><p>       
                For example, the following toolchain tarball is for a 64-bit development 
                host system and a 32-bit target architecture:
            </p><pre class="literallayout">
     poky-eglibc-x86_64-i586-toolchain-gmae-1.3.tar.bz2
            </pre><p>
                The toolchain tarballs are self-contained and must be installed into <code class="filename">/opt/poky</code>.
                The following commands show how you install the toolchain tarball given a 64-bit development 
                host system and a 32-bit target architecture.
                The example assumes the toolchain tarball is located in <code class="filename">~/toolchains/</code>.
                You must have your working directory set to root before unpacking the tarball:
            </p><p>
                </p><pre class="literallayout">
     $ cd /
     $ sudo tar -xvjf ~/toolchains/poky-eglibc-x86_64-i586-toolchain-gmae-1.3.tar.bz2
                </pre><p>
            </p><p>
                For more information on how to install tarballs, see the 
                "<a class="link" href="#using-an-existing-toolchain-tarball" target="_top">Using a Cross-Toolchain Tarball</a>" and 
                "<a class="link" href="#using-the-toolchain-from-within-the-build-tree" target="_top">Using BitBake and the Build Directory</a>" sections in the Yocto Project Application Developer's Guide.
            </p></div><div class="section" title="5.2.2. Downloading the Pre-Built Linux Kernel"><div class="titlepage"><div><div><h4 class="title"><a id="downloading-the-pre-built-linux-kernel"></a>5.2.2. Downloading the Pre-Built Linux Kernel</h4></div></div></div><p>
                You can download the pre-built Linux kernel suitable for running in the QEMU emulator from 
                <a class="ulink" href="http://downloads.yoctoproject.org/releases/yocto/yocto-1.3/machines/qemu" target="_top">http://downloads.yoctoproject.org/releases/yocto/yocto-1.3/machines/qemu</a>.
                Be sure to use the kernel that matches the architecture you want to simulate.
                Download areas exist for the five supported machine architectures:
                <code class="filename">qemuarm</code>, <code class="filename">qemumips</code>, <code class="filename">qemuppc</code>,
                <code class="filename">qemux86</code>, and <code class="filename">qemux86-64</code>.
            </p><p>  
                Most kernel files have one of the following forms:
                </p><pre class="literallayout">
     *zImage-qemu&lt;<span class="emphasis"><em>arch</em></span>&gt;.bin
     vmlinux-qemu&lt;<span class="emphasis"><em>arch</em></span>&gt;.bin

     Where:
         &lt;<span class="emphasis"><em>arch</em></span>&gt; is a string representing the target architecture: 
                x86, x86-64, ppc, mips, or arm.
                </pre><p>
            </p><p>
                You can learn more about downloading a Yocto Project kernel in the 
                "<a class="link" href="#local-kernel-files" target="_top">Yocto Project Kernel</a>" 
                bulleted item in the Yocto Project Development Manual.
            </p></div><div class="section" title="5.2.3. Downloading the Filesystem"><div class="titlepage"><div><div><h4 class="title"><a id="downloading-the-filesystem"></a>5.2.3. Downloading the Filesystem</h4></div></div></div><p>
                You can also download the filesystem image suitable for your target architecture from
                <a class="ulink" href="http://downloads.yoctoproject.org/releases/yocto/yocto-1.3/machines/qemu" target="_top">http://downloads.yoctoproject.org/releases/yocto/yocto-1.3/machines/qemu</a>.
                Again, be sure to use the filesystem that matches the architecture you want 
                to simulate.
            </p><p>
                The filesystem image has two tarball forms: <code class="filename">ext3</code> and 
                <code class="filename">tar</code>.
                You must use the <code class="filename">ext3</code> form when booting an image using the 
                QEMU emulator.
                The <code class="filename">tar</code> form can be flattened out in your host development system
                and used for build purposes with the Yocto Project.
                </p><pre class="literallayout">
     core-image-&lt;<span class="emphasis"><em>profile</em></span>&gt;-qemu&lt;<span class="emphasis"><em>arch</em></span>&gt;.ext3
     core-image-&lt;<span class="emphasis"><em>profile</em></span>&gt;-qemu&lt;<span class="emphasis"><em>arch</em></span>&gt;.tar.bz2

     Where:
         &lt;<span class="emphasis"><em>profile</em></span>&gt; is the filesystem image's profile:
                   lsb, lsb-dev, lsb-sdk, lsb-qt3, minimal, minimal-dev, sato, sato-dev, or sato-sdk.
                   For information on these types of image profiles, see the
                   "<a class="link" href="#ref-images" target="_top">Images</a>" chapter
                   in the Yocto Project Reference Manual.

         &lt;<span class="emphasis"><em>arch</em></span>&gt; is a string representing the target architecture: 
                x86, x86-64, ppc, mips, or arm.
                </pre><p>
            </p></div><div class="section" title="5.2.4. Setting Up the Environment and Starting the QEMU Emulator"><div class="titlepage"><div><div><h4 class="title"><a id="setting-up-the-environment-and-starting-the-qemu-emulator"></a>5.2.4. Setting Up the Environment and Starting the QEMU Emulator</h4></div></div></div><p>
                Before you start the QEMU emulator, you need to set up the emulation environment.
                The following command form sets up the emulation environment.
                </p><pre class="literallayout">
     $ source /opt/poky/1.3/environment-setup-&lt;<span class="emphasis"><em>arch</em></span>&gt;-poky-linux-&lt;<span class="emphasis"><em>if</em></span>&gt; 

     Where:
         &lt;<span class="emphasis"><em>arch</em></span>&gt; is a string representing the target architecture: 
                i586, x86_64, ppc603e, mips, or armv5te.

         &lt;<span class="emphasis"><em>if</em></span>&gt; is a string representing an embedded application binary interface.
              Not all setup scripts include this string.
                </pre><p>
            </p><p>
                Finally, this command form invokes the QEMU emulator 
                </p><pre class="literallayout">
     $ runqemu &lt;<span class="emphasis"><em>qemuarch</em></span>&gt; &lt;<span class="emphasis"><em>kernel-image</em></span>&gt; &lt;<span class="emphasis"><em>filesystem-image</em></span>&gt;

     Where:
         &lt;<span class="emphasis"><em>qemuarch</em></span>&gt; is a string representing the target architecture: qemux86, qemux86-64, 
                    qemuppc, qemumips, or qemuarm.

         &lt;<span class="emphasis"><em>kernel-image</em></span>&gt; is the architecture-specific kernel image.

         &lt;<span class="emphasis"><em>filesystem-image</em></span>&gt; is the .ext3 filesystem image.

                </pre><p>
            </p><p>
                Continuing with the example, the following two commands setup the emulation 
                environment and launch QEMU.
                This example assumes the root filesystem (<code class="filename">.ext3</code> file) and 
                the pre-built kernel image file both reside in your home directory. 
                The kernel and filesystem are for a 32-bit target architecture.
                </p><pre class="literallayout">
     $ cd $HOME
     $ source /opt/poky/1.3/environment-setup-i586-poky-linux 
     $ runqemu qemux86 bzImage-qemux86.bin \
     core-image-sato-qemux86.ext3
                </pre><p>
            </p><p>
                The environment in which QEMU launches varies depending on the filesystem image and on the 
                target architecture.  
                For example, if you source the environment for the ARM target 
                architecture and then boot the minimal QEMU image, the emulator comes up in a new 
                shell in command-line mode.  
                However, if you boot the SDK image, QEMU comes up with a GUI.
                </p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>Booting the PPC image results in QEMU launching in the same shell in 
                command-line mode.</div><p>
            </p></div></div></div><div class="section" title="6. Super User"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="super-user"></a>6. Super User 
</h2></div></div></div><p>
        This section 
        <sup>[<a id="id1482592" href="#ftn.id1482592" class="footnote">1</a>]</sup>
        gives you a very fast description of how to use the Yocto Project to build images 
        for a BeagleBoard xM starting from scratch. 
        The steps were performed on a 64-bit Ubuntu 10.04 system.
    </p><div class="section" title="6.1. Getting the Yocto Project"><div class="titlepage"><div><div><h3 class="title"><a id="getting-yocto"></a>6.1. Getting the Yocto Project</h3></div></div></div><p>
            Set up your <a class="link" href="#source-directory" target="_top">source directory</a>
            one of two ways:
            </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><span class="emphasis"><em>Tarball:</em></span> 
                    Use if you want the latest stable release:
                    </p><pre class="literallayout">
     $ wget http://downloads.yoctoproject.org/releases/yocto/yocto-1.3/poky-1.2+snapshot-8.0.tar.bz2
     $ tar xvjf poky-1.2+snapshot-8.0.tar.bz2
                    </pre></li><li class="listitem"><p><span class="emphasis"><em>Git Repository:</em></span>
                    Use if you want to work with cutting edge development content:
                    </p><pre class="literallayout">
     $ git clone git://git.yoctoproject.org/poky
                    </pre></li></ul></div><p>
            The remainder of the section assumes the Git repository method.
        </p></div><div class="section" title="6.2. Setting Up Your Host"><div class="titlepage"><div><div><h3 class="title"><a id="setting-up-your-host"></a>6.2. Setting Up Your Host</h3></div></div></div><p>
            You need some packages for everything to work. 
            Rather than duplicate them here, look at the "<a class="link" href="#packages" title="4.2. The Packages">The Packages</a>"
            section earlier in this quick start.
        </p></div><div class="section" title="6.3. Initializing the Build Environment"><div class="titlepage"><div><div><h3 class="title"><a id="initializing-the-build-environment"></a>6.3. Initializing the Build Environment</h3></div></div></div><p>
            From the parent directory of local source directory, initialize your environment 
            and provide a meaningful 
            <a class="link" href="#build-directory" target="_top">build directory</a>
            name:
            </p><pre class="literallayout">
     $ source poky/oe-init-build-env mybuilds
            </pre><p>
            At this point, the <code class="filename">mybuilds</code> directory has been created for you 
            and it is now your current working directory.
            If you don't provide your own directory name it defaults to <code class="filename">build</code>.
        </p></div><div class="section" title="6.4. Configuring the local.conf File"><div class="titlepage"><div><div><h3 class="title"><a id="configuring-the-local.conf-file"></a>6.4. Configuring the local.conf File</h3></div></div></div><p>
            Initializing the build environment creates a <code class="filename">conf/local.conf</code> configuration file
            in the build directory.
            You need to manually edit this file to specify the machine you are building and to optimize
            your build time.
            Here are the minimal changes to make:
            </p><pre class="literallayout">
     BB_NUMBER_THREADS = "8"
     PARALLEL_MAKE = "-j 8"
     MACHINE ?= "beagleboard"
            </pre><p>
            Briefly, set <a class="link" href="#var-BB_NUMBER_THREADS" target="_top"><code class="filename">BB_NUMBER_THREADS</code></a> 
            and <a class="link" href="#var-PARALLEL_MAKE" target="_top"><code class="filename">PARALLEL_MAKE</code></a> to
            twice your host processor's number of cores.
        </p><p>
            A good deal that goes into a Yocto Project build is simply downloading all of the source 
            tarballs. 
            Maybe you have been working with another build system (OpenEmbedded, Angstrom, etc) for which 
            you've built up a sizable directory of source tarballs.
            Or perhaps someone else has such a directory for which you have read access. 
            If so, you can save time by adding the <code class="filename">PREMIRRORS</code>
            statement to your configuration file so that local directories are first checked for existing 
            tarballs before running out to the net:
            </p><pre class="literallayout">
     PREMIRRORS_prepend = "\
     git://.*/.* file:///home/you/dl/ \n \
     svn://.*/.* file:///home/you/dl/ \n \
     cvs://.*/.* file:///home/you/dl/ \n \
     ftp://.*/.* file:///home/you/dl/ \n \
     http://.*/.* file:///home/you/dl/ \n \
     https://.*/.* file:///home/you/dl/ \n"
            </pre><p>
        </p></div><div class="section" title="6.5. Building the Image"><div class="titlepage"><div><div><h3 class="title"><a id="building-the-image"></a>6.5. Building the Image</h3></div></div></div><p>
            At this point, you need to select an image to build for the BeagleBoard xM.
            If this is your first build using the Yocto Project, you should try the smallest and simplest
            image:
            </p><pre class="literallayout">
     $ bitbake core-image-minimal
            </pre><p>
            Now you just wait for the build to finish.
        </p><p>
            Here are some variations on the build process that could be helpful:
            </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>Fetch all the necessary sources without starting the build:
                    </p><pre class="literallayout">
     $ bitbake -c fetchall core-image-minimal
                    </pre><p>
                    This variation guarantees that you have all the sources for that BitBake target 
                    should you to disconnect from the net and want to do the build later offline.
                    </p></li><li class="listitem"><p>Specify to continue the build even if BitBake encounters an error.
                    By default, BitBake aborts the build when it encounters an error.
                    This command keeps a faulty build going:
                    </p><pre class="literallayout">
     $ bitbake -k core-image-minimal
                    </pre></li></ul></div><p>
        </p><p>
            Once you have your image, you can take steps to load and boot it on the target hardware.
        </p></div></div><div class="footnotes"><br /><hr width="100" align="left" /><div class="footnote"><p><sup>[<a id="ftn.id1482592" href="#id1482592" class="para">1</a>] </sup>
                Kudos and thanks to Robert P. J. Day of 
                <a class="ulink" href="http://www.crashcourse.ca" target="_top">CrashCourse</a> for providing the basis
                for this "expert" section with information from one of his
                <a class="ulink" href="http://www.crashcourse.ca/wiki/index.php/Yocto_Project_Quick_Start" target="_top">wiki</a>
                pages.
            </p></div></div></div>

<table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="100%"><tr><td align="left"><img src="figures/dev-title.png" align="left" width="100%" /></td></tr></table> 

    <div xml:lang="en" class="book" lang="en"><div class="titlepage"><div><div><h1 class="title"><a id="dev-manual"></a></h1></div><div><div class="authorgroup">
            <div class="author"><h3 class="author"><span class="firstname">Scott</span> <span class="surname">Rifenbark</span></h3><div class="affiliation">
                    <span class="orgname">Intel Corporation<br /></span>
                </div><code class="email">&lt;<a class="email" href="mailto:scott.m.rifenbark@intel.com">scott.m.rifenbark@intel.com</a>&gt;</code></div>
        </div></div><div><p class="copyright">Copyright © 2010-2012 Linux Foundation</p></div><div><div class="legalnotice" title="Legal Notice"><a id="id1482939"></a>
      <p>
          Permission is granted to copy, distribute and/or modify this document under 
          the terms of the <a class="ulink" href="http://creativecommons.org/licenses/by-sa/2.0/uk/" target="_top">
          Creative Commons Attribution-Share Alike 2.0 UK: England &amp; Wales</a> as published by 
          Creative Commons.
      </p>

      <div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
          Due to production processes, there could be differences between the Yocto Project
          documentation bundled in the release tarball and the
          Yocto Project Development Manual on
          the <a class="ulink" href="http://www.yoctoproject.org" target="_top">Yocto Project</a> website.
          For the latest version of this manual, see the manual on the website.
      </div>
    </div></div><div><div class="revhistory"><table border="1" width="100%" summary="Revision history"><tr><th align="left" valign="top" colspan="2"><b>Revision History</b></th></tr>
            <tr><td align="left">Revision 1.1</td><td align="left">6 October 2011</td></tr><tr><td align="left" colspan="2">The initial document released with the Yocto Project 1.1 Release.</td></tr>
            <tr><td align="left">Revision 1.2</td><td align="left">April 2012</td></tr><tr><td align="left" colspan="2">Released with the Yocto Project 1.2 Release.</td></tr>
            <tr><td align="left">Revision 1.3</td><td align="left">Sometime in 2012</td></tr><tr><td align="left" colspan="2">Released with the Yocto Project 1.3 Release.</td></tr>
        </table></div></div></div><hr /></div>
    

    <div class="chapter" title="Chapter 1. The Yocto Project Development Manual"><div class="titlepage"><div><div><h2 class="title"><a id="dev-manual-intro"></a>Chapter 1. The Yocto Project Development Manual</h2></div></div></div><div class="toc"><dl><dt><span class="section"><a href="#intro">1.1. Introduction</a></span></dt><dt><span class="section"><a href="#what-this-manual-provides">1.2. What this Manual Provides</a></span></dt><dt><span class="section"><a href="#what-this-manual-does-not-provide">1.3. What this Manual Does Not Provide</a></span></dt><dt><span class="section"><a href="#other-information">1.4. Other Information</a></span></dt></dl></div><div class="section" title="1.1. Introduction"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="intro"></a>1.1. Introduction</h2></div></div></div><p>
            Welcome to the Yocto Project Development Manual!
            This manual gives you an idea of how to use the Yocto Project to develop embedded Linux 
            images and user-space applications to run on targeted devices. 
            Reading this manual gives you an overview of image, kernel, and user-space application development
            using the Yocto Project. 
            Because much of the information in this manual is general, it contains many references to other
            sources where you can find more detail.
            For example, detailed information on Git, repositories and open source in general
            can be found in many places.  
            Another example is how to get set up to use the Yocto Project, which our Yocto Project 
            Quick Start covers.
        </p><p>  
            The Yocto Project Development Manual, however, does provide detailed examples on how to create a 
            Board Support Package (BSP), change the kernel source code, and reconfigure the kernel.
            You can find this information in the appendices of the manual.
        </p></div><div class="section" title="1.2. What this Manual Provides"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="what-this-manual-provides"></a>1.2. What this Manual Provides</h2></div></div></div><p>
            The following list describes what you can get from this guide:
            </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>Information that lets you get set 
                    up to develop using the Yocto Project.</p></li><li class="listitem"><p>Information to help developers who are new to the open source environment 
                    and to the distributed revision control system Git, which the Yocto Project 
                    uses.</p></li><li class="listitem"><p>An understanding of common end-to-end development models and tasks.</p></li><li class="listitem"><p>Development case overviews for both system development and user-space 
                    applications.</p></li><li class="listitem"><p>An overview and understanding of the emulation environment used with 
                    the Yocto Project (QEMU).</p></li><li class="listitem"><p>An understanding of basic kernel architecture and concepts.</p></li><li class="listitem"><p>Many references to other sources of related information.</p></li></ul></div><p>
        </p></div><div class="section" title="1.3. What this Manual Does Not Provide"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="what-this-manual-does-not-provide"></a>1.3. What this Manual Does Not Provide</h2></div></div></div><p>
            This manual will not give you the following:
            </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>Step-by-step instructions if those instructions exist in other Yocto 
                    Project documentation.  
                    For example, the Yocto Project Development Manual contains detailed 
                    instruction on how to obtain and configure the 
                    <span class="trademark">Eclipse</span>™ Yocto Plug-in.</p></li><li class="listitem"><p>Reference material.  
                    This type of material resides in an appropriate reference manual.  
                    For example, system variables are documented in the 
                    Yocto Project Reference Manual.</p></li><li class="listitem"><p>Detailed public information that is not specific to the Yocto Project.  
                    For example, exhaustive information on how to use Git is covered better through the 
                    Internet than in this manual.</p></li></ul></div><p>
        </p></div><div class="section" title="1.4. Other Information"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="other-information"></a>1.4. Other Information</h2></div></div></div><p>
            Because this manual presents overview information for many different topics, you will
            need to supplement it with other information.
            The following list presents other sources of information you might find helpful:
            </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><span class="emphasis"><em>The <a class="ulink" href="http://www.yoctoproject.org" target="_top">Yocto Project Website</a>:
                    </em></span> The home page for the Yocto Project provides lots of information on the project 
                    as well as links to software and documentation.</p></li><li class="listitem"><p><span class="emphasis"><em>
                    Yocto Project Quick Start:</em></span> This short document lets you get started 
                    with the Yocto Project quickly and start building an image.</p></li><li class="listitem"><p><span class="emphasis"><em> 
                    Yocto Project Reference Manual:</em></span> This manual is a reference 
                    guide to the OpenEmbedded build system known as "Poky."  
                    The manual also contains a reference chapter on Board Support Package (BSP) 
                    layout.</p></li><li class="listitem"><p><span class="emphasis"><em>
                    Yocto Project Application Developer's Guide:</em></span>
                    This guide provides information that lets you get going with the Application 
                    Development Toolkit (ADT) and stand-alone cross-development toolchains to 
                    develop projects using the Yocto Project.</p></li><li class="listitem"><p><span class="emphasis"><em>
                    Yocto Project Board Support Package (BSP) Developer's Guide:</em></span>
                    This guide defines the structure for BSP components.  
                    Having a commonly understood structure encourages standardization.</p></li><li class="listitem"><p><span class="emphasis"><em>
                    Yocto Project Kernel Architecture and Use Manual:</em></span>
                    This manual describes the architecture of the Yocto Project kernel and provides 
                    some work flow examples.</p></li><li class="listitem"><p><span class="emphasis"><em>
                    <a class="ulink" href="http://www.youtube.com/watch?v=3ZlOu-gLsh0" target="_top">
                    Eclipse IDE Yocto Plug-in</a>:</em></span> A step-by-step instructional video that
                    demonstrates how an application developer uses Yocto Plug-in features within 
                    the Eclipse IDE.</p></li><li class="listitem"><p><span class="emphasis"><em>
                    <a class="ulink" href="https://wiki.yoctoproject.org/wiki/FAQ" target="_top">FAQ</a>:</em></span>
                    A list of commonly asked questions and their answers.</p></li><li class="listitem"><p><span class="emphasis"><em>
                    <a class="ulink" href="http://www.yoctoproject.org/download/yocto/yocto-project-1.1-release-notes-poky-8.0" target="_top">
                    Release Notes</a>:</em></span> Features, updates and known issues for the current 
                    release of the Yocto Project.</p></li><li class="listitem"><p><span class="emphasis"><em>
                    <a class="ulink" href="http://www.yoctoproject.org/projects/hob" target="_top">
                    Hob</a>:</em></span> A graphical user interface for BitBake. 
                    Hob's primary goal is to enable a user to perform common tasks more easily.</p></li><li class="listitem"><p><span class="emphasis"><em>
                    <a class="ulink" href="http://www.yoctoproject.org/documentation/build-appliance" target="_top">
                    Build Appliance</a>:</em></span> A bootable custom embedded Linux image you can 
                    either build using a non-Linux development system (VMware applications) or download 
                    from the Yocto Project website.
                    See the <a class="ulink" href="http://www.yoctoproject.org/documentation/build-appliance" target="_top">Build Appliance</a>
                    page for more information.</p></li><li class="listitem"><p><span class="emphasis"><em>
                    <a class="ulink" href="http://bugzilla.yoctoproject.org" target="_top">Bugzilla</a>:</em></span>
                    The bug tracking application the Yocto Project uses.
                    If you find problems with the Yocto Project, you should report them using this
                    application.</p></li><li class="listitem"><p><span class="emphasis"><em>
                    Yocto Project Mailing Lists:</em></span> To subscribe to the Yocto Project mailing 
                    lists, click on the following URLs and follow the instructions:
                    </p><div class="itemizedlist"><ul class="itemizedlist" type="circle"><li class="listitem"><p><a class="ulink" href="http://lists.yoctoproject.org/listinfo/yocto" target="_top">http://lists.yoctoproject.org/listinfo/yocto</a> for a 
                            Yocto Project Discussions mailing list.</p></li><li class="listitem"><p><a class="ulink" href="http://lists.yoctoproject.org/listinfo/poky" target="_top">http://lists.yoctoproject.org/listinfo/poky</a> for a 
                            Yocto Project Discussions mailing list about the Poky build system.</p></li><li class="listitem"><p><a class="ulink" href="http://lists.yoctoproject.org/listinfo/yocto-announce" target="_top">http://lists.yoctoproject.org/listinfo/yocto-announce</a>
                            for a mailing list to receive official Yocto Project announcements for developments and
                            as well as Yocto Project milestones.</p></li></ul></div></li><li class="listitem"><p><span class="emphasis"><em>Internet Relay Chat (IRC):</em></span>
                    Two IRC channels on freenode are available 
                    for Yocto Project and Poky discussions: <code class="filename">#yocto</code> and 
                    <code class="filename">#poky</code>, respectively.</p></li><li class="listitem"><p><span class="emphasis"><em>
                    <a class="ulink" href="http://o-hand.com" target="_top">OpenedHand</a>:</em></span>
                    The company that initially developed the Poky project, which is the basis
                    for the OpenEmbedded build system used by the Yocto Project.
                    OpenedHand was acquired by Intel Corporation in 2008.</p></li><li class="listitem"><p><span class="emphasis"><em>
                    <a class="ulink" href="http://www.intel.com/" target="_top">Intel Corporation</a>:</em></span>
                    A multinational semiconductor chip manufacturer company whose Software and 
                    Services Group created and supports the Yocto Project.
                    Intel acquired OpenedHand in 2008.</p></li><li class="listitem"><p><span class="emphasis"><em>
                    <a class="ulink" href="http://www.openembedded.org" target="_top">OpenEmbedded</a>:</em></span>
                    The build system used by the Yocto Project. 
                    This project is the upstream, generic, embedded distribution from which the Yocto 
                    Project derives its build system (Poky) from and to which it contributes.</p></li><li class="listitem"><p><span class="emphasis"><em>
                    <a class="ulink" href="http://developer.berlios.de/projects/bitbake/" target="_top">
                    BitBake</a>:</em></span> The tool used by the OpenEmbedded build system 
                    to process project metadata.</p></li><li class="listitem"><p><span class="emphasis"><em>
                    <a class="ulink" href="http://docs.openembedded.org/bitbake/html/" target="_top">
                    BitBake User Manual</a>:</em></span> A comprehensive guide to the BitBake tool.
                    </p></li><li class="listitem"><p><span class="emphasis"><em>
                    <a class="ulink" href="http://wiki.qemu.org/Index.html" target="_top">QEMU</a>:
                    </em></span> An open-source machine emulator and virtualizer.</p></li></ul></div><p>
        </p></div></div>

    <div class="chapter" title="Chapter 2. Getting Started with the Yocto Project"><div class="titlepage"><div><div><h2 class="title"><a id="dev-manual-start"></a>Chapter 2. Getting Started with the Yocto Project</h2></div></div></div><div class="toc"><dl><dt><span class="section"><a href="#introducing-the-yocto-project">2.1. Introducing the Yocto Project</a></span></dt><dt><span class="section"><a href="#getting-setup">2.2. Getting Set Up</a></span></dt><dt><span class="section"><a href="#building-images">2.3. Building Images</a></span></dt><dt><span class="section"><a href="#using-pre-built-binaries-and-qemu">2.4. Using Pre-Built Binaries and QEMU</a></span></dt></dl></div><p>
    This chapter introduces the Yocto Project and gives you an idea of what you need to get started.  
    You can find enough information to set up your development host and build or use images for 
    hardware supported by the Yocto Project by reading the 
    Yocto Project Quick Start.
</p><p>
    The remainder of this chapter summarizes what is in the Yocto Project Quick Start and provides 
    some higher-level concepts you might want to consider.
</p><div class="section" title="2.1. Introducing the Yocto Project"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="introducing-the-yocto-project"></a>2.1. Introducing the Yocto Project</h2></div></div></div><p>
        The Yocto Project is an open-source collaboration project focused on embedded Linux development.  
        The project currently provides a build system, which is 
        referred to as the OpenEmbedded build system in the Yocto Project documentation.
        The Yocto Project provides various ancillary tools suitable for the embedded developer  
        and also features the Sato reference User Interface, which is optimized for 
        stylus driven, low-resolution screens.
    </p><p>
        You can use the OpenEmbedded build system, which uses 
        <a class="ulink" href="http://docs.openembedded.org/bitbake/html/" target="_top">BitBake</a>, to develop complete Linux 
        images and associated user-space applications for architectures based on ARM, MIPS, PowerPC, 
        x86 and x86-64.  
        While the Yocto Project does not provide a strict testing framework,
        it does provide or generate for you artifacts that let you perform target-level and 
        emulated testing and debugging.  
        Additionally, if you are an <span class="trademark">Eclipse</span>™
        IDE user, you can install an Eclipse Yocto Plug-in to allow you to 
        develop within that familiar environment.
    </p></div><div class="section" title="2.2. Getting Set Up"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="getting-setup"></a>2.2. Getting Set Up</h2></div></div></div><p>
        Here is what you need to get set up to use the Yocto Project:
        </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><span class="emphasis"><em>Host System:</em></span>  You should have a reasonably current 
                Linux-based host system.
                You will have the best results with a recent release of Fedora, 
                OpenSUSE, Ubuntu, or CentOS as these releases are frequently tested against the Yocto Project
                and officially supported.  
                You should also have about 100 gigabytes of free disk space for building images.
                </p></li><li class="listitem"><p><span class="emphasis"><em>Packages:</em></span>  The OpenEmbedded build system
                requires certain packages exist on your development system (e.g. Python 2.6 or 2.7).  
                See "<a class="link" href="#packages" target="_top">The Packages</a>" 
                section in the Yocto Project Quick Start for the exact package
                requirements and the installation commands to install them 
                for the supported distributions.</p></li><li class="listitem"><p><a id="local-yp-release"></a><span class="emphasis"><em>Yocto Project Release:</em></span>  
                You need a release of the Yocto Project.  
                You set up a with local <a class="link" href="#source-directory">source directory</a>
                one of two ways depending on whether you 
                are going to contribute back into the Yocto Project or not.
                </p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
                    Regardless of the method you use, this manual refers to the resulting local
                    hierarchical set of files as the "source directory."
                </div><p>
                </p><div class="itemizedlist"><ul class="itemizedlist" type="circle"><li class="listitem"><p><span class="emphasis"><em>Tarball Extraction:</em></span>  If you are not going to contribute 
                        back into the Yocto Project, you can simply download a Yocto Project release you want 
                        from the website’s <a class="ulink" href="http://www.yoctoproject.org/download" target="_top">download page</a>.
                        Once you have the tarball, just extract it into a directory of your choice.</p><p>For example, the following command extracts the Yocto Project 1.3 
                        release tarball 
                        into the current working directory and sets up the local source directory
                        with a top-level folder named <code class="filename">poky-1.2+snapshot-8.0</code>:
                        </p><pre class="literallayout">
     $ tar xfj poky-1.2+snapshot-8.0.tar.bz2
                        </pre><p>This method does not produce a local Git repository. 
                        Instead, you simply end up with a snapshot of the release.</p></li><li class="listitem"><p><span class="emphasis"><em>Git Repository Method:</em></span>  If you are going to be contributing
                        back into the Yocto Project or you simply want to keep up
                        with the latest developments, you should use Git commands to set up a local
                        Git repository of the upstream <code class="filename">poky</code> source repository.
                        Doing so creates a repository with a complete history of changes and allows 
                        you to easily submit your changes upstream to the project.
                        Because you cloned the repository, you have access to all the Yocto Project development
                        branches and tag names used in the upstream repository.</p><p>The following transcript shows how to clone the <code class="filename">poky</code>  
                        Git repository into the current working directory.
                        </p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>You can view the Yocto Project Source Repositories at
                        <a class="ulink" href="http://git.yoctoproject.org/cgit.cgi" target="_top">http://git.yoctoproject.org/cgit.cgi</a></div><p>  
                        The command creates the local repository in a directory named <code class="filename">poky</code>.
                        For information on Git used within the Yocto Project, see the
                        "<a class="link" href="#git" title="3.6. Git">Git</a>" section.
                        </p><pre class="literallayout">
     $ git clone git://git.yoctoproject.org/poky
     Initialized empty Git repository in /home/scottrif/poky/.git/
     remote: Counting objects: 141863, done.
     remote: Compressing objects: 100% (38624/38624), done.
     remote: Total 141863 (delta 99661), reused 141816 (delta 99614)
     Receiving objects: 100% (141863/141863), 76.64 MiB | 126 KiB/s, done.
     Resolving deltas: 100% (99661/99661), done.
                        </pre><p>For another example of how to set up your own local Git repositories, see this
                        <a class="ulink" href="https://wiki.yoctoproject.org/wiki/Transcript:_from_git_checkout_to_meta-intel_BSP" target="_top">
                        wiki page</a>, which describes how to create both <code class="filename">poky</code>
                        and <code class="filename">meta-intel</code> Git repositories.</p></li></ul></div></li><li class="listitem"><p><a id="local-kernel-files"></a><span class="emphasis"><em>Yocto Project Kernel:</em></span>  
                If you are going to be making modifications to a supported Yocto Project kernel, you 
                need to establish local copies of the source.
                You can find Git repositories of supported Yocto Project Kernels organized under
                "Yocto Project Linux Kernel" in the Yocto Project Source Repositories at
                <a class="ulink" href="http://git.yoctoproject.org/cgit.cgi" target="_top">http://git.yoctoproject.org/cgit.cgi</a>.</p><p>This setup involves creating a bare clone of the Yocto Project kernel and then 
                copying that cloned repository.
                You can create the bare clone and the copy of the bare clone anywhere you like.
                For simplicity, it is recommended that you create these structures outside of the 
                source directory (usually <code class="filename">poky</code>).</p><p>As an example, the following transcript shows how to create the bare clone
                of the <code class="filename">linux-yocto-3.2</code> kernel and then create a copy of 
                that clone.
                </p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>When you have a local Yocto Project kernel Git repository, you can 
                reference that repository rather than the upstream Git repository as 
                part of the <code class="filename">clone</code> command.
                Doing so can speed up the process.</div><p>In the following example, the bare clone is named 
                <code class="filename">linux-yocto-3.2.git</code>, while the 
                copy is named <code class="filename">my-linux-yocto-3.2-work</code>: 
                </p><pre class="literallayout">
     $ git clone --bare git://git.yoctoproject.org/linux-yocto-3.2 linux-yocto-3.2.git
     Initialized empty Git repository in /home/scottrif/linux-yocto-3.2.git/
     remote: Counting objects: 2468027, done.
     remote: Compressing objects: 100% (392255/392255), done.
     remote: Total 2468027 (delta 2071693), reused 2448773 (delta 2052498)
     Receiving objects: 100% (2468027/2468027), 530.46 MiB | 129 KiB/s, done.
     Resolving deltas: 100% (2071693/2071693), done.
                </pre><p>Now create a clone of the bare clone just created:
                </p><pre class="literallayout">
     $ git clone linux-yocto-3.2.git my-linux-yocto-3.2-work
     Initialized empty Git repository in /home/scottrif/my-linux-yocto-3.2-work/.git/
     Checking out files: 100% (37619/37619), done.
                </pre></li><li class="listitem"><p><a id="poky-extras-repo"></a><span class="emphasis"><em>
                The <code class="filename">poky-extras</code> Git Repository</em></span>:
                The <code class="filename">poky-extras</code> Git repository contains metadata needed 
                only if you are modifying and building the kernel image.
                In particular, it contains the kernel BitBake append (<code class="filename">.bbappend</code>)
                files that you 
                edit to point to your locally modified kernel source files and to build the kernel
                image. 
                Pointing to these local files is much more efficient than requiring a download of the 
                kernel's source files from upstream each time you make changes to the kernel.</p><p>You can find the <code class="filename">poky-extras</code> Git Repository in the 
                "Yocto Metadata Layers" area of the Yocto Project Source Repositories at 
                <a class="ulink" href="http://git.yoctoproject.org/cgit.cgi" target="_top">http://git.yoctoproject.org/cgit.cgi</a>.
                It is good practice to create this Git repository inside the source directory.</p><p>Following is an example that creates the <code class="filename">poky-extras</code> Git 
                repository inside the source directory, which is named <code class="filename">poky</code> 
                in this case:
                </p><pre class="literallayout">
     $ git clone git://git.yoctoproject.org/poky-extras poky-extras
     Initialized empty Git repository in /home/scottrif/poky/poky-extras/.git/
     remote: Counting objects: 618, done.
     remote: Compressing objects: 100% (558/558), done.
     remote: Total 618 (delta 192), reused 307 (delta 39)
     Receiving objects: 100% (618/618), 526.26 KiB | 111 KiB/s, done.
     Resolving deltas: 100% (192/192), done.
                </pre></li><li class="listitem"><p><a id="supported-board-support-packages-(bsps)"></a><span class="emphasis"><em>Supported Board 
                Support Packages (BSPs):</em></span>  
                The Yocto Project provides a layer called <code class="filename">meta-intel</code> and 
                it is maintained in its own separate Git repository.
                The <code class="filename">meta-intel</code> layer contains many supported 
                <a class="link" href="#bsp-layers" target="_top">BSP Layers</a>.</p><p>Similar considerations exist for setting up the <code class="filename">meta-intel</code>
                layer.  
                You can get set up for BSP development one of two ways: tarball extraction or
                with a local Git repository.
                It is a good idea to use the same method that you used to set up the source directory.
                Regardless of the method you use, the Yocto Project uses the following BSP layer 
                naming scheme:
                </p><pre class="literallayout"> 
     meta-&lt;BSP_name&gt; 
                </pre><p>
                where &lt;BSP_name&gt; is the recognized BSP name.
                Here are some examples:
                </p><pre class="literallayout">
     meta-crownbay
     meta-emenlow
     meta-n450
                </pre><p>
                See the
                "<a class="link" href="#bsp-layers" target="_top">BSP Layers</a>"
                section in the Yocto Project Board Support Package (BSP) Developer's Guide for more
                information on BSP Layers.
                </p><div class="itemizedlist"><ul class="itemizedlist" type="circle"><li class="listitem"><p><span class="emphasis"><em>Tarball Extraction:</em></span>  You can download any released 
                        BSP tarball from the same 
                        <a class="ulink" href="http://www.yoctoproject.org/download" target="_top">download site</a> used 
                        to get the Yocto Project release.  
                        Once you have the tarball, just extract it into a directory of your choice.
                        Again, this method just produces a snapshot of the BSP layer in the form
                        of a hierarchical directory structure.</p></li><li class="listitem"><p><span class="emphasis"><em>Git Repository Method:</em></span>  If you are working 
                        with a local Git repository for your source directory, you should also use this method 
                        to set up the <code class="filename">meta-intel</code> Git repository.
                        You can locate the <code class="filename">meta-intel</code> Git repository in the 
                        "Yocto Metadata Layers" area of the Yocto Project Source Repositories at
                        <a class="ulink" href="http://git.yoctoproject.org/cgit.cgi" target="_top">http://git.yoctoproject.org/cgit.cgi</a>.</p><p>Typically, you set up the <code class="filename">meta-intel</code> Git repository inside
                        the source directory.
                        For example, the following transcript shows the steps to clone the 
                        <code class="filename">meta-intel</code>
                        Git repository inside the local <code class="filename">poky</code> Git repository.
                        </p><pre class="literallayout">
     $ git clone git://git.yoctoproject.org/meta-intel.git
     Initialized empty Git repository in /home/scottrif/poky/meta-intel/.git/
     remote: Counting objects: 3380, done.
     remote: Compressing objects: 100% (2750/2750), done.
     remote: Total 3380 (delta 1689), reused 227 (delta 113)
     Receiving objects: 100% (3380/3380), 1.77 MiB | 128 KiB/s, done.
     Resolving deltas: 100% (1689/1689), done.
                        </pre><p>The same  
                        <a class="ulink" href="https://wiki.yoctoproject.org/wiki/Transcript:_from_git_checkout_to_meta-intel_BSP" target="_top">
                        wiki page</a> referenced earlier covers how to 
                        set up the <code class="filename">meta-intel</code> Git repository.</p></li></ul></div></li><li class="listitem"><p><span class="emphasis"><em>Eclipse Yocto Plug-in:</em></span>  If you are developing 
                applications using the Eclipse Integrated Development Environment (IDE),
                you will need this plug-in.  
                See the 
                "<a class="link" href="#setting-up-the-eclipse-ide" title="5.2.2.1. Setting Up the Eclipse IDE">Setting up the Eclipse IDE</a>"
                section for more information.</p></li></ul></div><p>
    </p></div><div class="section" title="2.3. Building Images"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="building-images"></a>2.3. Building Images</h2></div></div></div><p>
        The build process creates an entire Linux distribution, including the toolchain, from source.  
        For more information on this topic, see the 
        "<a class="link" href="#building-image" target="_top">Building an Image</a>"
        section in the Yocto Project Quick Start.
    </p><p>
        The build process is as follows:
        </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>Make sure you have set up the source directory described in the 
                previous section.</p></li><li class="listitem"><p>Initialize the build environment by sourcing a build environment 
                script.</p></li><li class="listitem"><p>Optionally ensure the <code class="filename">conf/local.conf</code> configuration file,
                which is found in the 
                <a class="link" href="#build-directory">build directory</a>, 
                is set up how you want it.  
                This file defines many aspects of the build environment including 
                the target machine architecture through the 
                <code class="filename"><a class="link" href="#var-MACHINE" target="_top">MACHINE</a></code> variable, 
                the development machine's processor use through the 
                <code class="filename"><a class="link" href="#var-BB_NUMBER_THREADS" target="_top">BB_NUMBER_THREADS</a></code> and 
                <code class="filename"><a class="link" href="#var-PARALLEL_MAKE" target="_top">PARALLEL_MAKE</a></code> variables, and
                a centralized tarball download directory through the  
                <code class="filename"><a class="link" href="#var-DL_DIR" target="_top">DL_DIR</a></code> variable.</p></li><li class="listitem"><p>Build the image using the <code class="filename">bitbake</code> command.
                If you want information on BitBake, see the user manual at
                <a class="ulink" href="http://docs.openembedded.org/bitbake/html" target="_top">http://docs.openembedded.org/bitbake/html</a>.</p></li><li class="listitem"><p>Run the image either on the actual hardware or using the QEMU 
                emulator.</p></li></ol></div><p>
    </p></div><div class="section" title="2.4. Using Pre-Built Binaries and QEMU"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="using-pre-built-binaries-and-qemu"></a>2.4. Using Pre-Built Binaries and QEMU</h2></div></div></div><p>
        Another option you have to get started is to use pre-built binaries. 
        The Yocto Project provides many types of binaries with each release. 
        See the <a class="link" href="#ref-images" target="_top">Images</a>
        chapter in the Yocto Project Reference Manual
        for descriptions of the types of binaries that ship with a Yocto Project
        release.
    </p><p>
        Using a pre-built binary is ideal for developing software applications to run on your 
        target hardware.  
        To do this, you need to be able to access the appropriate cross-toolchain tarball for 
        the architecture on which you are developing.  
        If you are using an SDK type image, the image ships with the complete toolchain native to 
        the architecture. 
        If you are not using an SDK type image, you need to separately download and 
        install the stand-alone Yocto Project cross-toolchain tarball.
    </p><p>
        Regardless of the type of image you are using, you need to download the pre-built kernel 
        that you will boot in the QEMU emulator and then download and extract the target root 
        filesystem for your target machine’s architecture.
        You can get architecture-specific binaries and filesystem from
        <a class="ulink" href="http://downloads.yoctoproject.org/releases/yocto/yocto-1.3/machines" target="_top">machines</a>.
        You can get stand-alone toolchains from
        <a class="ulink" href="http://downloads.yoctoproject.org/releases/yocto/yocto-1.3/toolchain/" target="_top">toolchains</a>.
        Once you have all your files, you set up the environment to emulate the hardware 
        by sourcing an environment setup script. 
        Finally, you start the QEMU emulator.
        You can find details on all these steps in the 
        "<a class="link" href="#using-pre-built" target="_top">Using Pre-Built Binaries and QEMU</a>"
        section of the Yocto Project Quick Start. 
    </p><p> 
        Using QEMU to emulate your hardware can result in speed issues
        depending on the target and host architecture mix.
        For example, using the <code class="filename">qemux86</code> image in the emulator 
        on an Intel-based 32-bit (x86) host machine is fast because the target and 
        host architectures match.
        On the other hand, using the <code class="filename">qemuarm</code> image on the same Intel-based
        host can be slower.
        But, you still achieve faithful emulation of ARM-specific issues. 
    </p><p>
        To speed things up, the QEMU images support using <code class="filename">distcc</code>
        to call a cross-compiler outside the emulated system. 
        If you used <code class="filename">runqemu</code> to start QEMU, and the
        <code class="filename">distccd</code> application is present on the host system, any 
        BitBake cross-compiling toolchain available from the build system is automatically
        used from within QEMU simply by calling <code class="filename">distcc</code>.
        You can accomplish this by defining the cross-compiler variable 
        (e.g. <code class="filename">export CC="distcc"</code>).
        Alternatively, if you are using a suitable SDK image or the appropriate
        stand-alone toolchain is present in <code class="filename">/opt/poky</code>,
        the toolchain is also automatically used.
    </p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>
        Several mechanisms exist that let you connect to the system running on the 
        QEMU emulator:
        <div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>QEMU provides a framebuffer interface that makes standard 
                consoles available.</p></li><li class="listitem"><p>Generally, headless embedded devices have a serial port.
                If so, you can configure the operating system of the running image
                to use that port to run a console. 
                The connection uses standard IP networking.</p></li><li class="listitem"><p>SSH servers exist in some QEMU images.
                The <code class="filename">core-image-sato</code> QEMU image has a Dropbear secure 
                shell (ssh) server that runs with the root password disabled.
                The <code class="filename">core-image-basic</code> and <code class="filename">core-image-lsb</code> QEMU images 
                have OpenSSH instead of Dropbear.
                Including these SSH servers allow you to use standard <code class="filename">ssh</code> and 
                <code class="filename">scp</code> commands.
                The <code class="filename">core-image-minimal</code> QEMU image, however, contains no ssh 
                server.</p></li><li class="listitem"><p>You can use a provided, user-space NFS server to boot the QEMU session 
                using a local copy of the root filesystem on the host.
                In order to make this connection, you must extract a root filesystem tarball by using the 
                <code class="filename">runqemu-extract-sdk</code> command.
                After running the command, you must then point the <code class="filename">runqemu</code>
                script to the extracted directory instead of a root filesystem image file.</p></li></ul></div></div></div></div>

    <div class="chapter" title="Chapter 3. The Yocto Project Open Source Development Environment"><div class="titlepage"><div><div><h2 class="title"><a id="dev-manual-newbie"></a>Chapter 3. The Yocto Project Open Source Development Environment</h2></div></div></div><div class="toc"><dl><dt><span class="section"><a href="#open-source-philosophy">3.1. Open Source Philosophy</a></span></dt><dt><span class="section"><a href="#usingpoky-changes-collaborate">3.2. Using the Yocto Project in a Team Environment</a></span></dt><dt><span class="section"><a href="#yocto-project-repositories">3.3. Yocto Project Source Repositories</a></span></dt><dt><span class="section"><a href="#yocto-project-terms">3.4. Yocto Project Terms</a></span></dt><dt><span class="section"><a href="#licensing">3.5. Licensing</a></span></dt><dt><span class="section"><a href="#git">3.6. Git</a></span></dt><dd><dl><dt><span class="section"><a href="#repositories-tags-and-branches">3.6.1. Repositories, Tags, and Branches</a></span></dt><dt><span class="section"><a href="#basic-commands">3.6.2. Basic Commands</a></span></dt></dl></dd><dt><span class="section"><a href="#workflows">3.7. Workflows</a></span></dt><dt><span class="section"><a href="#tracking-bugs">3.8. Tracking Bugs</a></span></dt><dt><span class="section"><a href="#how-to-submit-a-change">3.9. How to Submit a Change</a></span></dt><dd><dl><dt><span class="section"><a href="#pushing-a-change-upstream">3.9.1. Using Scripts to Push a Change Upstream and Request a Pull</a></span></dt><dt><span class="section"><a href="#submitting-a-patch">3.9.2. Using Email to Submit a Patch</a></span></dt></dl></dd></dl></div><p>
    This chapter helps you understand the Yocto Project as an open source development project.
    In general, working in an open source environment is very different from working in a 
    closed, proprietary environment.  
    Additionally, the Yocto Project uses specific tools and constructs as part of its development 
    environment.  
    This chapter specifically addresses open source philosophy, licensing issues, code repositories, 
    the open source distributed version control system Git, and best practices using the Yocto Project.
</p><div class="section" title="3.1. Open Source Philosophy"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="open-source-philosophy"></a>3.1. Open Source Philosophy</h2></div></div></div><p>
        Open source philosophy is characterized by software development directed by peer production 
        and collaboration through an active community of developers.
        Contrast this to the more standard centralized development models used by commercial software 
        companies where a finite set of developers produces a product for sale using a defined set
        of procedures that ultimately result in an end product whose architecture and source material
        are closed to the public.
    </p><p>
        Open source projects conceptually have differing concurrent agendas, approaches, and production.   
        These facets of the development process can come from anyone in the public (community) that has a 
        stake in the software project.  
        The open source environment contains new copyright, licensing, domain, and consumer issues 
        that differ from the more traditional development environment.  
        In an open source environment, the end product, source material, and documentation are
        all available to the public at no cost.
    </p><p>
        A benchmark example of an open source project is the Linux Kernel, which was initially conceived 
        and created by Finnish computer science student Linus Torvalds in 1991.  
        Conversely, a good example of a non-open source project is the 
        <span class="trademark">Windows</span>® family of operating 
        systems developed by <span class="trademark">Microsoft</span>® Corporation.
    </p><p>
        Wikipedia has a good historical description of the Open Source Philosophy  
        <a class="ulink" href="http://en.wikipedia.org/wiki/Open_source" target="_top">here</a>. 
        You can also find helpful information on how to participate in the Linux Community 
        <a class="ulink" href="http://ldn.linuxfoundation.org/book/how-participate-linux-community" target="_top">here</a>.
    </p></div><div class="section" title="3.2. Using the Yocto Project in a Team Environment"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="usingpoky-changes-collaborate"></a>3.2. Using the Yocto Project in a Team Environment</h2></div></div></div><p>
        It might not be immediately clear how you can use the Yocto Project in a team environment, 
        or scale it for a large team of developers. 
        The specifics of any situation determine the best solution.
        Granted that the Yocto Project offers immense flexibility regarding this, practices do exist 
        that experience has shown work well.
    </p><p>
        The core component of any development effort with the Yocto Project is often an 
        automated build and testing framework along with an image generation process. 
        You can use these core components to check that the metadata can be built, 
        highlight when commits break the build, and provide up-to-date images that 
        allow developers to test the end result and use it as a base platform for further 
        development. 
        Experience shows that buildbot is a good fit for this role. 
        What works well is to configure buildbot to make two types of builds:
        incremental and full (from scratch).  
        See <a class="ulink" href="http://autobuilder.yoctoproject.org:8010/" target="_top">the buildbot for the 
        Yocto Project</a> for an example implementation that uses buildbot.
    </p><p>
        You can tie incremental builds to a commit hook that triggers the build
        each time a commit is made to the metadata.  
        This practice results in useful acid tests that determine whether a given commit 
        breaks the build in some serious way. 
        Associating a build to a commit can catch a lot of simple errors.
        Furthermore, the tests are fast so developers can get quick feedback on changes.
    </p><p>
        Full builds build and test everything from the ground up. 
        These types of builds usually happen at predetermined times like during the 
        night when the machine load is low.
    </p><p>
        Most teams have many pieces of software undergoing active development at any given time. 
        You can derive large benefits by putting these pieces under the control of a source 
        control system that is compatible (i.e. Git or Subversion (SVN)) with the OpenEmbeded 
        build system that the Yocto Project uses.
        You can then set the autobuilder to pull the latest revisions of the packages 
        and test the latest commits by the builds.
        This practice quickly highlights issues. 
        The build system easily supports testing configurations that use both a 
        stable known good revision and a floating revision.
        The build system can also take just the changes from specific source control branches.
        This capability allows you to track and test specific changes.
    </p><p>
        Perhaps the hardest part of setting this up is defining the software project or 
        the metadata policies that surround the different source control systems.
        Of course circumstances will be different in each case.
        However, this situation reveals one of the Yocto Project's advantages - 
        the system itself does not
        force any particular policy on users, unlike a lot of build systems. 
        The system allows the best policies to be chosen for the given circumstances.
    </p></div><div class="section" title="3.3. Yocto Project Source Repositories"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="yocto-project-repositories"></a>3.3. Yocto Project Source Repositories</h2></div></div></div><p>
        The Yocto Project team maintains complete source repositories for all Yocto Project files 
        at <a class="ulink" href="http://git.yoctoproject.org/cgit/cgit.cgi" target="_top">http://git.yoctoproject.org/cgit/cgit.cgi</a>.
        This web-based source code browser is organized into categories by function such as
        IDE Plugins, Matchbox, Poky, Yocto Linux Kernel, and so forth.
        From the interface, you can click on any particular item in the "Name" column and 
        see the URL at the bottom of the page that you need to set up a Git repository for 
        that particular item.
        Having a local Git repository of the source directory (poky) allows you to 
        make changes, contribute to the history, and ultimately enhance the Yocto Project's 
        tools, Board Support Packages, and so forth.
    </p><p>  
        Conversely, if you are a developer that is not interested in contributing back to the 
        Yocto Project, you have the ability to simply download and extract release tarballs
        and use them within the Yocto Project environment.
        All that is required is a particular release of the Yocto Project and 
        your application source code.  
    </p><p>
        For any supported release of Yocto Project, you can go to the Yocto Project website’s 
        <a class="ulink" href="http://www.yoctoproject.org/download" target="_top">download page</a> and get a 
        tarball of the release.  
        You can also go to this site to download any supported BSP tarballs.
        Unpacking the tarball gives you a hierarchical source directory that lets you develop 
        using the Yocto Project.
    </p><p>
        Once you are set up through either tarball extraction or creation of Git repositories, 
        you are ready to develop.
    </p><p>
        In summary, here is where you can get the project files needed for development:
        </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><a id="source-repositories"></a><span class="emphasis"><em><a class="ulink" href="http://git.yoctoproject.org/cgit/cgit.cgi" target="_top">Source Repositories:</a></em></span>
                This area contains IDE Plugins, Matchbox, Poky, Poky Support, Tools, Yocto Linux Kernel, and Yocto 
                Metadata Layers.
                You can create local copies of Git repositories for each of these areas.</p><p>
                </p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="540"><tr style="height: 360px"><td align="center"><img src="figures/source-repos.png" align="middle" width="540" /></td></tr></table><p>
                </p></li><li class="listitem"><p><a id="index-downloads"></a><span class="emphasis"><em><a class="ulink" href="http://downloads.yoctoproject.org/releases/" target="_top">Index of /releases:</a></em></span>
                This area contains index releases such as 
                the <span class="trademark">Eclipse</span>™
                Yocto Plug-in, miscellaneous support, poky, pseudo, cross-development toolchains,
                and all released versions of Yocto Project in the form of images or tarballs.
                Downloading and extracting these files does not produce a local copy of the 
                Git repository but rather a snapshot of a particular release or image.</p><p>
                </p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="540"><tr style="height: 360px"><td align="center"><img src="figures/index-downloads.png" align="middle" width="540" /></td></tr></table><p>
                </p></li><li class="listitem"><p><span class="emphasis"><em><a class="ulink" href="http://www.yoctoproject.org/download" target="_top">Yocto Project Download Page</a></em></span>
                This page on the Yocto Project website allows you to download any Yocto Project
                release or Board Support Package (BSP) in tarball form.
                The tarballs are similar to those found in the 
                <a class="ulink" href="http://downloads.yoctoproject.org/releases/" target="_top">Index of /releases:</a> area.</p><p>
                </p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="540"><tr style="height: 360px"><td align="center"><img src="figures/yp-download.png" align="middle" width="540" /></td></tr></table><p>
            </p></li></ul></div><p>
    </p></div><div class="section" title="3.4. Yocto Project Terms"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="yocto-project-terms"></a>3.4. Yocto Project Terms</h2></div></div></div><p>
        Following is a list of terms and definitions users new to the Yocto Project development 
        environment might find helpful.
        While some of these terms are universal, the list includes them just in case:
        </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><span class="emphasis"><em>Append Files:</em></span> Files that append build information to 
                a recipe file.
                Append files are known as BitBake append files and <code class="filename">.bbappend</code> files.
                The OpenEmbedded build system expects every append file to have a corresponding and 
                underlying recipe (<code class="filename">.bb</code>) file.
                Furthermore, the append file and the underlying recipe must have the same root filename.
                The filenames can differ only in the file type suffix used (e.g. 
                <code class="filename">formfactor_0.0.bb</code> and <code class="filename">formfactor_0.0.bbappend</code>).
                </p><p>Information in append files overrides the information in the similarly-named recipe file.
                For examples of <code class="filename">.bbappend</code> file in use, see the
                "<a class="link" href="#using-bbappend-files" title="4.1.4. Using .bbappend Files">Using .bbappend Files</a>" and 
                "<a class="link" href="#changing-recipes-kernel" title="A.5.2.4. Changing  recipes-kernel">Changing <code class="filename">recipes-kernel</code></a>"
                sections.</p></li><li class="listitem"><p><span class="emphasis"><em>BitBake:</em></span> The task executor and scheduler used by 
                the OpenEmbedded build system to build images. 
                For more information on BitBake, see the <a class="ulink" href="http://docs.openembedded.org/bitbake/html/" target="_top">
                BitBake documentation</a>.</p></li><li class="listitem"><p><a id="build-directory"></a><span class="emphasis"><em>Build Directory:</em></span>
                This term refers to the area used by the OpenEmbedded build system for builds.  
                The area is created when you <code class="filename">source</code> the setup 
                environment script that is found in the source directory
                (i.e. <code class="filename">oe-init-build-env</code>).
                The <a class="link" href="#var-TOPDIR" target="_top"><code class="filename">TOPDIR</code></a>
                variable points to the build directory.</p><p>You have a lot of flexibility when creating the build directory.
                Following are some examples that show how to create the directory:
                   </p><div class="itemizedlist"><ul class="itemizedlist" type="circle"><li class="listitem"><p>Create the build directory in your current working directory
                            and name it <code class="filename">build</code>.
                            This is the default behavior.
                            </p><pre class="literallayout">
     $ source oe-init-build-env
                            </pre></li><li class="listitem"><p>Provide a directory path and specifically name the build 
                            directory. 
                            This next example creates a build directory named <code class="filename">YP-8.0</code>
                            in your home directory within the directory <code class="filename">mybuilds</code>.
                            If <code class="filename">mybuilds</code> does not exist, the directory is created for you:
                            </p><pre class="literallayout"> 
     $ source poky-1.2+snapshot-8.0/oe-init-build-env $HOME/mybuilds/YP-8.0
                            </pre></li><li class="listitem"><p>Provide an existing directory to use as the build directory.
                            This example uses the existing <code class="filename">mybuilds</code> directory 
                            as the build directory.
                            </p><pre class="literallayout"> 
     $ source poky-1.2+snapshot-8.0/oe-init-build-env $HOME/mybuilds/
                            </pre></li></ul></div><p> 
                </p></li><li class="listitem"><p><span class="emphasis"><em>Build System:</em></span> In the context of the Yocto Project 
                this term refers to the OpenEmbedded build system used by the project. 
                This build system is based on the project known as "Poky."
                For some historical information about Poky, see the 
                <a class="link" href="#poky">poky</a> term further along in this section.
                </p></li><li class="listitem"><p><span class="emphasis"><em>Classes:</em></span> Files that provide for logic encapsulation
                and inheritance allowing commonly used patterns to be defined once and easily used 
                in multiple recipes.  
                Class files end with the <code class="filename">.bbclass</code> filename extension.
                </p></li><li class="listitem"><p><span class="emphasis"><em>Configuration File:</em></span>  Configuration information in various
                <code class="filename">.conf</code> files provides global definitions of variables.
                The <code class="filename">conf/local.conf</code> configuration file in the 
                <a class="link" href="#build-directory">build directory</a>
                contains user-defined variables that affect each build.
                The <code class="filename">meta-yocto/conf/distro/poky.conf</code> configuration file
                defines Yocto ‘distro’ configuration
                variables used only when building with this policy.  
                Machine configuration files, which 
                are located throughout the 
                <a class="link" href="#source-directory">source directory</a>, define
                variables for specific hardware and are only used when building for that target 
                (e.g. the <code class="filename">machine/beagleboard.conf</code> configuration file defines 
                variables for the Texas Instruments ARM Cortex-A8 development board).  
                Configuration files end with a <code class="filename">.conf</code> filename extension.
                </p></li><li class="listitem"><p><span class="emphasis"><em>Cross-Development Toolchain:</em></span> 
                A collection of software development
                tools and utilities that allow you to develop software for targeted architectures.
                This toolchain contains cross-compilers, linkers, and debuggers that are specific to 
                an architecture.
                You can use the OpenEmbedded build system to build cross-development toolchains in tarball 
                form that, when
                unpacked, contain the development tools you need to cross-compile and test your software.
                The Yocto Project ships with images that contain toolchains for supported architectures
                as well.
                Sometimes this toolchain is referred to as the meta-toolchain.</p></li><li class="listitem"><p><span class="emphasis"><em>Image:</em></span> An image is the result produced when 
                BitBake processes a given collection of recipes and related metadata.
                Images are the binary output that run on specific hardware and for specific
                use cases.
                For a list of the supported image types that the Yocto Project provides, see the
                "<a class="link" href="#ref-images" target="_top">Images</a>"
                chapter in the Yocto Project Reference Manual.</p></li><li class="listitem"><p><a id="layer"></a><span class="emphasis"><em>Layer:</em></span> A collection of recipes representing the core, 
                a BSP, or an application stack.
                For a discussion on BSP Layers, see the 
                "<a class="link" href="#bsp-layers" target="_top">BSP Layers</a>"
                section in the Yocto Project Board Support Packages (BSP) Developer's Guide.</p></li><li class="listitem"><p><a id="metadata"></a><span class="emphasis"><em>Metadata:</em></span> The files that BitBake parses when 
                building an image. 
                Metadata includes recipes, classes, and configuration files.</p></li><li class="listitem"><p><span class="emphasis"><em>OE-Core:</em></span> A core set of metadata originating 
                with OpenEmbedded (OE) that is shared between OE and the Yocto Project.
                This metadata is found in the <code class="filename">meta</code> directory of the source
                directory.</p></li><li class="listitem"><p><span class="emphasis"><em>Package:</em></span> The packaged output from a baked recipe.
                A package is generally the compiled binaries produced from the recipe's sources.  
                You ‘bake’ something by running it through BitBake.</p></li><li class="listitem"><p><a id="poky"></a><span class="emphasis"><em>Poky:</em></span> The term "poky" can mean several things.
                In its most general sence, it is an open-source project that was initially developed
                by OpenedHand.  With OpenedHand, poky was developed off of the existing OpenEmbedded
                build system becoming a build system for embedded images. 
                After Intel Corporation aquired OpenedHand, the project poky became the basis for 
                the Yocto Project's build system.
                Within the Yocto Project source repositories, poky exists as a separate Git repository
                that can be cloned to yield a local copy on the host system. 
                Thus, "poky" can refer to the local copy of the source directory used to develop within
                the Yocto Project.</p></li><li class="listitem"><p><span class="emphasis"><em>Recipe:</em></span> A set of instructions for building packages.  
                A recipe describes where you get source code and which patches to apply.
                Recipes describe dependencies for libraries or for other recipes, and they 
                also contain configuration and compilation options.  
                Recipes contain the logical unit of execution, the software/images to build, and 
                use the <code class="filename">.bb</code> file extension.</p></li><li class="listitem"><p><a id="source-directory"></a><span class="emphasis"><em>Source Directory:</em></span>
                This term refers to the directory structure created as a result of either downloading 
                and unpacking a Yocto Project release tarball or creating a local copy of 
                <code class="filename">poky</code> Git repository <code class="filename">git://git.yoctoproject.org/poky</code>.
                Sometimes you might here the term "poky directory" used to refer to this 
                directory structure.</p><p>The source directory contains BitBake, Documentation, metadata and 
                other files that all support the Yocto Project. 
                Consequently, you must have the source directory in place on your development 
                system in order to do any development using the Yocto Project.</p><p>For tarball expansion, the name of the top-level directory of the source directory  
                is derived from the Yocto Project release tarball.
                For example, downloading and unpacking <code class="filename">poky-1.2+snapshot-8.0.tar.bz2</code>
                results in a source directory whose top-level folder is named 
                <code class="filename">poky-1.2+snapshot-8.0</code>.
                If you create a local copy of the Git repository, then you can name the repository 
                anything you like.
                Throughout much of the documentation, <code class="filename">poky</code> is used as the name of 
                the top-level folder of the local copy of the poky Git repository.
                So, for example, cloning the <code class="filename">poky</code> Git repository results in a 
                local Git repository whose top-level folder is also named <code class="filename">poky</code>.</p><p>It is important to understand the differences between the source directory created
                by unpacking a released tarball as compared to cloning 
                <code class="filename">git://git.yoctoproject.org/poky</code>.
                When you unpack a tarball, you have an exact copy of the files based on the time of 
                release - a fixed release point.
                Any changes you make to your local files in the source directory are on top of the release.
                On the other hand, when you clone the <code class="filename">poky</code> Git repository, you have an
                active development repository.
                In this case, any local changes you make to the source directory can be later applied 
                to active development branches of the upstream <code class="filename">poky</code> Git 
                repository.</p><p>Finally, if you want to track a set of local changes while starting from the same point
                as a release tarball, you can create a local Git branch that 
                reflects the exact copy of the files at the time of their release. 
                You do this using Git tags that are part of the repository.</p><p>For more information on concepts around Git repositories, branches, and tags,
                see the  
                "<a class="link" href="#repositories-tags-and-branches" title="3.6.1. Repositories, Tags, and Branches">Repositories, Tags, and Branches</a>"
                section.</p></li><li class="listitem"><p><span class="emphasis"><em>Tasks:</em></span> Arbitrary groups of software Recipes.  
                You simply use Tasks to hold recipes that, when built, usually accomplish a single task.  
                For example, a task could contain the recipes for a company’s proprietary or value-add software.  
                Or, the task could contain the recipes that enable graphics. 
                A task is really just another recipe.  
                Because task files are recipes, they end with the <code class="filename">.bb</code> filename 
                extension.</p></li><li class="listitem"><p><span class="emphasis"><em>Upstream:</em></span> A reference to source code or repositories
                that are not local to the development system but located in a master area that is controlled
                by the maintainer of the source code.
                For example, in order for a developer to work on a particular piece of code, they need to 
                first get a copy of it from an "upstream" source.</p></li></ul></div><p>
    </p></div><div class="section" title="3.5. Licensing"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="licensing"></a>3.5. Licensing</h2></div></div></div><p>
        Because open source projects are open to the public, they have different licensing structures in place.  
        License evolution for both Open Source and Free Software has an interesting history.  
        If you are interested in this history, you can find basic information here:
    </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><a class="ulink" href="http://en.wikipedia.org/wiki/Open-source_license" target="_top">Open source license history</a>
            </p></li><li class="listitem"><p><a class="ulink" href="http://en.wikipedia.org/wiki/Free_software_license" target="_top">Free software license
            history</a></p></li></ul></div><p>
    </p><p>
        In general, the Yocto Project is broadly licensed under the Massachusetts Institute of Technology 
        (MIT) License.  
        MIT licensing permits the reuse of software within proprietary software as long as the 
        license is distributed with that software.  
        MIT is also compatible with the GNU General Public License (GPL).  
        Patches to the Yocto Project follow the upstream licensing scheme.
        You can find information on the MIT license at  
        <a class="ulink" href="http://www.opensource.org/licenses/mit-license.php" target="_top">here</a>.
        You can find information on the GNU GPL <a class="ulink" href="http://www.opensource.org/licenses/LGPL-3.0" target="_top">
        here</a>. 
    </p><p>
        When you build an image using Yocto Project, the build process uses a known list of licenses to 
        ensure compliance.
        You can find this list in the Yocto Project files directory at 
        <code class="filename">meta/files/common-licenses</code>.  
        Once the build completes, the list of all licenses found and used during that build are 
        kept in the 
        <a class="link" href="#build-directory">build directory</a> at 
        <code class="filename">tmp/deploy/images/licenses</code>.
    </p><p>  
        If a module requires a license that is not in the base list, the build process 
        generates a warning during the build.  
        These tools make it easier for a developer to be certain of the licenses with which
        their shipped products must comply.
        However, even with these tools it is still up to the developer to resolve potential licensing issues.
    </p><p>
        The base list of licenses used by the build process is a combination of the Software Package 
        Data Exchange (SPDX) list and the Open Source Initiative (OSI) projects.  
        <a class="ulink" href="http://spdx.org" target="_top">SPDX Group</a> is a working group of the Linux Foundation 
        that maintains a specification 
        for a standard format for communicating the components, licenses, and copyrights 
        associated with a software package.  
        <a class="ulink" href="http://opensource.org" target="_top">OSI</a> is a corporation dedicated to the Open Source 
        Definition and the effort for reviewing and approving licenses that are OSD-conformant.  
    </p><p>
        You can find a list of the combined SPDX and OSI licenses that the Yocto Project uses 
        <a class="ulink" href="http://git.yoctoproject.org/cgit/cgit.cgi/poky/tree/meta/files/common-licenses" target="_top">here</a>.
        This wiki page discusses the license infrastructure used by the Yocto Project.
    </p></div><div class="section" title="3.6. Git"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="git"></a>3.6. Git</h2></div></div></div><p>
        The Yocto Project uses Git, which is a free, open source distributed version control system.  
        Git supports distributed development, non-linear development, and can handle large projects.  
        It is best that you have some fundamental understanding of how Git tracks projects and 
        how to work with Git if you are going to use Yocto Project for development. 
        This section provides a quick overview of how Git works and provides you with a summary
        of some essential Git commands.
    </p><p>
        For more information on Git, see
        <a class="ulink" href="http://git-scm.com/documentation" target="_top">http://git-scm.com/documentation</a>.   
        If you need to download Git, go to <a class="ulink" href="http://git-scm.com/download" target="_top">http://git-scm.com/download</a>. 
    </p><div class="section" title="3.6.1. Repositories, Tags, and Branches"><div class="titlepage"><div><div><h3 class="title"><a id="repositories-tags-and-branches"></a>3.6.1. Repositories, Tags, and Branches</h3></div></div></div><p>
            As mentioned earlier in section 
            "<a class="link" href="#yocto-project-repositories" title="3.3. Yocto Project Source Repositories">Yocto Project Source Repositories</a>",
            the Yocto Project maintains source repositories at 
            <a class="ulink" href="http://git.yoctoproject.org/cgit.cgi" target="_top">http://git.yoctoproject.org/cgit.cgi</a>.
            If you look at this web-interface of the repositories, each item is a separate
            Git repository.
        </p><p>
            Git repositories use branching techniques that track content change (not files) 
            within a project (e.g. a new feature or updated documentation).  
            Creating a tree-like structure based on project divergence allows for excellent historical 
            information over the life of a project.  
            This methodology also allows for an environment in which you can do lots of 
            local experimentation on a project as you develop changes or new features.  
        </p><p>
            A Git repository represents all development efforts for a given project.
            For example, the Git repository <code class="filename">poky</code> contains all changes
            and developments for Poky over the course of its entire life. 
            That means that all changes that make up all releases are captured.
            The repository maintains a complete history of changes.
        </p><p>
            You can create a local copy of any repository by "cloning" it with the Git
            <code class="filename">clone</code> command.
            When you clone a Git repository, you end up with an identical copy of the 
            repository on your development system.  
            Once you have a local copy of a repository, you can take steps to develop locally.
            For examples on how to clone Git repositories, see the section
            "<a class="link" href="#getting-setup" title="2.2. Getting Set Up">Getting Set Up</a>" earlier in this manual.
        </p><p>
            It is important to understand that Git tracks content change and not files.
            Git uses "branches" to organize different development efforts. 
            For example, the <code class="filename">poky</code> repository has 
            <code class="filename">laverne</code>, <code class="filename">bernard</code>, 
            <code class="filename">edison</code>, <code class="filename">denzil</code> and 
            <code class="filename">master</code> branches among 
            others.
            You can see all the branches by going to  
            <a class="ulink" href="http://git.yoctoproject.org/cgit.cgi/poky/" target="_top">http://git.yoctoproject.org/cgit.cgi/poky/</a> and 
            clicking on the 
            <code class="filename"><a class="ulink" href="http://git.yoctoproject.org/cgit.cgi/poky/refs/heads" target="_top">[...]</a></code> 
            link beneath the "Branch" heading.
        </p><p>
            Each of these branches represents a specific area of development.
            The <code class="filename">master</code> branch represents the current or most recent 
            development.
            All other branches represent off-shoots of the <code class="filename">master</code>
            branch. 
        </p><p>
            When you create a local copy of a Git repository, the copy has the same set 
            of branches as the original.
            This means you can use Git to create a local working area (also called a branch)
            that tracks a specific development branch from the source Git repository.  
            in other words, you can define your local Git environment to work on any development
            branch in the repository.
            To help illustrate, here is a set of commands that creates a local copy of the 
            <code class="filename">poky</code> Git repository and then creates and checks out a local
            Git branch that tracks the Yocto Project 1.3 Release (1.2+snapshot) development:
            </p><pre class="literallayout">
     $ cd ~
     $ git clone git://git.yoctoproject.org/poky
     $ cd poky
     $ git checkout -b 1.2+snapshot origin/1.2+snapshot
            </pre><p>
            In this example, the name of the top-level directory of your local Yocto Project 
            Files Git repository is <code class="filename">poky</code>,
            and the name of the local working area (or local branch) you have created and checked
            out is <code class="filename">1.2+snapshot</code>.
            The files in your repository now reflect the same files that are in the 
            <code class="filename">1.2+snapshot</code> development branch of the Yocto Project's 
            <code class="filename">poky</code> repository.
            It is important to understand that when you create and checkout a 
            local working branch based on a branch name, 
            your local environment matches the "tip" of that development branch
            at the time you created your local branch, which could be
            different than the files at the time of a similarly named release.
            In other words, creating and checking out a local branch based on the 
            <code class="filename">1.2+snapshot</code> branch name is not the same as creating and 
            checking out a local branch based on the <code class="filename">1.2+snapshot-1.3</code>
            release.
            Keep reading to see how you create a local snapshot of a Yocto Project Release.
        </p><p>
            Git uses "tags" to mark specific changes in a repository.
            Typically, a tag is used to mark a special point such as the final change
            before a project is released.  
            You can see the tags used with the <code class="filename">poky</code> Git repository
            by going to <a class="ulink" href="http://git.yoctoproject.org/cgit.cgi/poky/" target="_top">http://git.yoctoproject.org/cgit.cgi/poky/</a> and 
            clicking on the 
            <code class="filename"><a class="ulink" href="http://git.yoctoproject.org/cgit.cgi/poky/refs/tags" target="_top">[...]</a></code> 
            link beneath the "Tag" heading.
        </p><p>
            Some key tags are <code class="filename">laverne-4.0</code>, <code class="filename">bernard-5.0</code>,
            and <code class="filename">1.2+snapshot-8.0</code>.
            These tags represent Yocto Project releases.
        </p><p>
            When you create a local copy of the Git repository, you also have access to all the 
            tags.
            Similar to branches, you can create and checkout a local working Git branch based 
            on a tag name. 
            When you do this, you get a snapshot of the Git repository that reflects 
            the state of the files when the change was made associated with that tag.
            The most common use is to checkout a working branch that matches a specific 
            Yocto Project release. 
            Here is an example:
            </p><pre class="literallayout">
     $ cd ~
     $ git clone git://git.yoctoproject.org/poky
     $ cd poky
     $ git checkout -b my-1.2+snapshot-8.0 1.2+snapshot-8.0
            </pre><p>
            In this example, the name of the top-level directory of your local Yocto Project 
            Files Git repository is <code class="filename">poky</code>.
            And, the name of the local branch you have created and checked out is
            <code class="filename">my-1.2+snapshot-8.0</code>.
            The files in your repository now exactly match the Yocto Project 1.3
            Release tag (<code class="filename">1.2+snapshot-8.0</code>).
            It is important to understand that when you create and checkout a local 
            working branch based on a tag, your environment matches a specific point 
            in time and not a development branch.
        </p></div><div class="section" title="3.6.2. Basic Commands"><div class="titlepage"><div><div><h3 class="title"><a id="basic-commands"></a>3.6.2. Basic Commands</h3></div></div></div><p>
            Git has an extensive set of commands that lets you manage changes and perform 
            collaboration over the life of a project.  
            Conveniently though, you can manage with a small set of basic operations and workflows 
            once you understand the basic philosophy behind Git.  
            You do not have to be an expert in Git to be functional.  
            A good place to look for instruction on a minimal set of Git commands is 
            <a class="ulink" href="http://git-scm.com/documentation" target="_top">here</a>.   
            If you need to download Git, you can do so 
            <a class="ulink" href="http://git-scm.com/download" target="_top">here</a>. 
        </p><p>
            If you don’t know much about Git, we suggest you educate            
            yourself by visiting the links previously mentioned.
        </p><p>
            The following list briefly describes some basic Git operations as a way to get started.  
            As with any set of commands, this list (in most cases) simply shows the base command and 
            omits the many arguments they support.  
            See the Git documentation for complete descriptions and strategies on how to use these commands:
            </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><span class="emphasis"><em><code class="filename">git init</code>:</em></span> Initializes an empty Git repository.  
                    You cannot use Git commands unless you have a <code class="filename">.git</code> repository.</p></li><li class="listitem"><p><span class="emphasis"><em><code class="filename">git clone</code>:</em></span> Creates a clone of a repository.  
                    During collaboration, this command allows you to create a local repository that is on 
                    equal footing with a fellow developer’s repository.</p></li><li class="listitem"><p><span class="emphasis"><em><code class="filename">git add</code>:</em></span> Adds updated file contents 
                    to the index that 
                    Git uses to track changes.  
                    You must add all files that have changed before you can commit them.</p></li><li class="listitem"><p><span class="emphasis"><em><code class="filename">git commit</code>:</em></span> Creates a “commit” that documents 
                    the changes you made.  
                    Commits are used for historical purposes, for determining if a maintainer of a project 
                    will allow the change, and for ultimately pushing the change from your local Git repository 
                    into the project’s upstream (or master) repository.</p></li><li class="listitem"><p><span class="emphasis"><em><code class="filename">git status</code>:</em></span> Reports any modified files that 
                    possibly need to be added and committed.</p></li><li class="listitem"><p><span class="emphasis"><em><code class="filename">git checkout &lt;branch-name&gt;</code>:</em></span> Changes 
                    your working branch.  
                    This command is analogous to “cd”.</p></li><li class="listitem"><p><span class="emphasis"><em><code class="filename">git checkout –b &lt;working-branch&gt;</code>:</em></span> Creates 
                    a working branch on your local machine where you can isolate work.  
                    It is a good idea to use local branches when adding specific features or changes.  
                    This way if you don’t like what you have done you can easily get rid of the work.</p></li><li class="listitem"><p><span class="emphasis"><em><code class="filename">git branch</code>:</em></span> Reports existing branches and 
                    tells you which branch in which you are currently working.</p></li><li class="listitem"><p><span class="emphasis"><em><code class="filename">git branch -D &lt;branch-name&gt;</code>:</em></span> 
                    Deletes an existing branch.  
                    You need to be in a branch other than the one you are deleting 
                    in order to delete &lt;branch-name&gt;.</p></li><li class="listitem"><p><span class="emphasis"><em><code class="filename">git pull</code>:</em></span> Retrieves information 
                    from an upstream Git 
                    repository and places it in your local Git repository.  
                    You use this command to make sure you are synchronized with the repository 
                    from which you are basing changes (.e.g. the master repository).</p></li><li class="listitem"><p><span class="emphasis"><em><code class="filename">git push</code>:</em></span> Sends all your local changes you 
                    have committed to an upstream Git repository (e.g. a contribution repository).  
                    The maintainer of the project draws from these repositories when adding your changes to the 
                    project’s master repository.</p></li><li class="listitem"><p><span class="emphasis"><em><code class="filename">git merge</code>:</em></span> Combines or adds changes from one 
                    local branch of your repository with another branch.  
                    When you create a local Git repository, the default branch is named “master”.  
                    A typical workflow is to create a temporary branch for isolated work, make and commit your 
                    changes, switch to your local master branch, merge the changes from the temporary branch into the 
                    local master branch, and then delete the temporary branch.</p></li><li class="listitem"><p><span class="emphasis"><em><code class="filename">git cherry-pick</code>:</em></span> Choose and apply specific 
                    commits from one branch into another branch.  
                    There are times when you might not be able to merge all the changes in one branch with 
                    another but need to pick out certain ones.</p></li><li class="listitem"><p><span class="emphasis"><em><code class="filename">gitk</code>:</em></span> Provides a GUI view of the branches 
                    and changes in your local Git repository.  
                    This command is a good way to graphically see where things have diverged in your 
                    local repository.</p></li><li class="listitem"><p><span class="emphasis"><em><code class="filename">git log</code>:</em></span> Reports a history of your changes to the 
                    repository.</p></li><li class="listitem"><p><span class="emphasis"><em><code class="filename">git diff</code>:</em></span> Displays line-by-line differences
                    between your local working files and the same files in the upstream Git repository that your 
                    branch currently tracks.</p></li></ul></div><p>
        </p></div></div><div class="section" title="3.7. Workflows"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="workflows"></a>3.7. Workflows</h2></div></div></div><p>
        This section provides some overview on workflows using Git.  
        In particular, the information covers basic practices that describe roles and actions in a 
        collaborative development environment.  
        Again, if you are familiar with this type of development environment, you might want to just 
        skip this section.
    </p><p>
        The Yocto Project files are maintained using Git in a "master" branch whose Git history 
        tracks every change and whose structure provides branches for all diverging functionality.
        Although there is no need to use Git, many open source projects do so.
        For the Yocto Project, a key individual called the "maintainer" is responsible for the "master"
        branch of the Git repository.
        The "master" branch is the “upstream” repository where the final builds of the project occur.  
        The maintainer is responsible for allowing changes in from other developers and for 
        organizing the underlying branch structure to reflect release strategies and so forth.  
        </p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>You can see who is the maintainer for Yocto Project files by examining the 
        <code class="filename">distro_tracking_fields.inc</code> file in the Yocto Project
        <code class="filename">meta/conf/distro/include</code> directory.</div><p>  
    </p><p>
        The project also has contribution repositories known as “contrib” areas.  
        These areas temporarily hold changes to the project that have been submitted or committed 
        by the Yocto Project development team and by community members that contribute to the project.  
        The maintainer determines if the changes are qualified to be moved from the "contrib" areas
        into the "master" branch of the Git repository.
    </p><p>
        Developers (including contributing community members) create and maintain cloned repositories 
        of the upstream "master" branch.  
        These repositories are local to their development platforms and are used to develop changes.  
        When a developer is satisfied with a particular feature or change, they “push” the changes 
        to the appropriate "contrib" repository.
    </p><p>  
        Developers are responsible for keeping their local repository up-to-date with "master".  
        They are also responsible for straightening out any conflicts that might arise within files 
        that are being worked on simultaneously by more than one person.  
        All this work is done locally on the developer’s machine before anything is pushed to a 
        "contrib" area and examined at the maintainer’s level.
    </p><p>
        A somewhat formal method exists by which developers commit changes and push them into the 
        "contrib" area and subsequently request that the maintainer include them into "master"  
        This process is called “submitting a patch” or “submitting a change.”  
    </p><p>
        To summarize the environment:  we have a single point of entry for changes into the project’s 
        "master" branch of the Git repository, which is controlled by the project’s maintainer.  
        And, we have a set of developers who independently develop, test, and submit changes 
        to "contrib" areas for the maintainer to examine.  
        The maintainer then chooses which changes are going to become a permanent part of the project.
    </p><p>
        </p><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0" width="540"><tr style="height: 270px"><td align="left"><img src="figures/git-workflow.png" align="left" height="270" /></td></tr></table><p>
    </p><p>
        While each development environment is unique, there are some best practices or methods 
        that help development run smoothly.  
        The following list describes some of these practices.  
        For more information about Git workflows, see the workflow topics in the 
        <a class="ulink" href="http://book.git-scm.com" target="_top">Git Community Book</a>. 
        </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><span class="emphasis"><em>Make Small Changes:</em></span> It is best to keep the changes you commit
                small as compared to bundling many disparate changes into a single commit.  
                This practice not only keeps things manageable but also allows the maintainer 
                to more easily include or refuse changes.</p><p>It is also good practice to leave the repository in a state that allows you to 
                still successfully build your project.  In other words, do not commit half of a feature,
                then add the other half in a separate, later commit.  
                Each commit should take you from one buildable project state to another 
                buildable state.</p></li><li class="listitem"><p><span class="emphasis"><em>Use Branches Liberally:</em></span> It is very easy to create, use, and 
                delete local branches in your working Git repository.  
                You can name these branches anything you like.  
                It is helpful to give them names associated with the particular feature or change 
                on which you are working.  
                Once you are done with a feature or change, simply discard the branch.</p></li><li class="listitem"><p><span class="emphasis"><em>Merge Changes:</em></span> The <code class="filename">git merge</code>
                command allows you to take the 
                changes from one branch and fold them into another branch.  
                This process is especially helpful when more than a single developer might be working 
                on different parts of the same feature.  
                Merging changes also automatically identifies any collisions or “conflicts” 
                that might happen as a result of the same lines of code being altered by two different 
                developers.</p></li><li class="listitem"><p><span class="emphasis"><em>Manage Branches:</em></span> Because branches are easy to use, you should 
                use a system where branches indicate varying levels of code readiness.  
                For example, you can have a “work” branch to develop in, a “test” branch where the code or 
                change is tested, a “stage” branch where changes are ready to be committed, and so forth.  
                As your project develops, you can merge code across the branches to reflect ever-increasing 
                stable states of the development.</p></li><li class="listitem"><p><span class="emphasis"><em>Use Push and Pull:</em></span> The push-pull workflow is based on the 
                concept of developers “pushing” local commits to a remote repository, which is 
                usually a contribution repository.  
                This workflow is also based on developers “pulling” known states of the project down into their 
                local development repositories.  
                The workflow easily allows you to pull changes submitted by other developers from the 
                upstream repository into your work area ensuring that you have the most recent software 
                on which to develop.
                The Yocto Project has two scripts named <code class="filename">create-pull-request</code> and 
                <code class="filename">send-pull-request</code> that ship with the release to facilitate this 
                workflow.
                You can find these scripts in the local Yocto Project files Git repository in
                the <code class="filename">scripts</code> directory.</p></li><li class="listitem"><p><span class="emphasis"><em>Patch Workflow:</em></span> This workflow allows you to notify the 
                maintainer through an email that you have a change (or patch) you would like considered 
                for the "master" branch of the Git repository.  
                To send this type of change you format the patch and then send the email using the Git commands 
                <code class="filename">git format-patch</code> and <code class="filename">git send-email</code>. 
                You can find information on how to submit later in this chapter.</p></li></ul></div><p>
    </p></div><div class="section" title="3.8. Tracking Bugs"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="tracking-bugs"></a>3.8. Tracking Bugs</h2></div></div></div><p>
        The Yocto Project uses its own implementation of 
        <a class="ulink" href="http://www.bugzilla.org/about/" target="_top">Bugzilla</a> to track bugs.  
        Implementations of Bugzilla work well for group development because they track bugs and code 
        changes, can be used to communicate changes and problems with developers, can be used to 
        submit and review patches, and can be used to manage quality assurance. 
        The home page for the Yocto Project implementation of Bugzilla is   
        <a class="ulink" href="http://bugzilla.yoctoproject.org" target="_top">http://bugzilla.yoctoproject.org</a>.
    </p><p>
        Sometimes it is helpful to submit, investigate, or track a bug against the Yocto Project itself
        such as when discovering an issue with some component of the build system that acts contrary 
        to the documentation or your expectations.  
        Following is the general procedure for submitting a new bug using the Yocto Project
        Bugzilla.
        You can find more information on defect management, bug tracking, and feature request
        processes all accomplished through the Yocto Project Bugzilla on the wiki page
        <a class="ulink" href="https://wiki.yoctoproject.org/wiki/Bugzilla_Configuration_and_Bug_Tracking" target="_top">here</a>.     
        </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>Always use the Yocto Project implementation of Bugzilla to submit
                a bug.</p></li><li class="listitem"><p>When submitting a new bug, be sure to choose the appropriate
                Classification, Product, and Component for which the issue was found.
                Defects for Yocto Project fall into one of four classifications:  Yocto Projects, 
                Infrastructure, Poky, and Yocto Metadata Layers.
                Each of these Classifications break down into multiple Products and, in some 
                cases, multiple Components.</p></li><li class="listitem"><p>Use the bug form to choose the correct Hardware and Architecture
                for which the bug applies.</p></li><li class="listitem"><p>Indicate the Yocto Project version you were using when the issue
                occurred.</p></li><li class="listitem"><p>Be sure to indicate the Severity of the bug.  
                Severity communicates how the bug impacted your work.</p></li><li class="listitem"><p>Provide a brief summary of the issue. 
                Try to limit your summary to just a line or two and be sure to capture the 
                essence of the issue.</p></li><li class="listitem"><p>Provide a detailed description of the issue.  
                You should provide as much detail as you can about the context, behavior, output, 
                and so forth that surround the issue.  
                You can even attach supporting files for output or log by using the "Add an attachment"
                button.</p></li><li class="listitem"><p>Submit the bug by clicking the "Submit Bug" button.</p></li></ol></div><p>
    </p></div><div class="section" title="3.9. How to Submit a Change"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="how-to-submit-a-change"></a>3.9. How to Submit a Change</h2></div></div></div><p>
        Contributions to the Yocto Project and OpenEmbedded are very welcome.
        Because the system is extremely configurable and flexible, we recognize that developers
        will want to extend, configure or optimize it for their specific uses.
        You should send patches to the appropriate mailing list so that they
        can be reviewed and merged by the appropriate maintainer.
        For a list of the Yocto Project and related mailing lists, see the
        "<a class="link" href="#resources-mailinglist" target="_top">Mailing lists</a>" section in 
        the Yocto Project Reference Manual.
    </p><p>
        The following is some guidance on which mailing list to use for what type of change:
        </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>For changes to the core metadata, send your patch to the
                <a class="ulink" href="http://lists.linuxtogo.org/cgi-bin/mailman/listinfo/openembedded-core" target="_top">openembedded-core</a> mailing list.
                For example, a change to anything under the <code class="filename">meta</code> or
                <code class="filename">scripts</code> directories
                should be sent to this mailing list.</p></li><li class="listitem"><p>For changes to BitBake (anything under the <code class="filename">bitbake</code>
                directory), send your patch to the
                <a class="ulink" href="http://lists.linuxtogo.org/cgi-bin/mailman/listinfo/bitbake-devel" target="_top">bitbake-devel</a> mailing list.</p></li><li class="listitem"><p>For changes to <code class="filename">meta-yocto</code>, send your patch to the
                <a class="ulink" href="http://lists.yoctoproject.org/listinfo/poky" target="_top">poky</a> mailing list.</p></li><li class="listitem"><p>For changes to other layers hosted on yoctoproject.org (unless the
                layer's documentation specifies otherwise), tools, and Yocto Project
                documentation, use the
                <a class="ulink" href="http://lists.yoctoproject.org/listinfo/yocto" target="_top">yocto</a> mailing list.</p></li><li class="listitem"><p>For additional recipes that do not fit into the core metadata,
                you should determine which layer the recipe should go into and submit the
                change in the manner recommended by the documentation (e.g. README) supplied
                with the layer. If in doubt, please ask on the
                <a class="ulink" href="http://lists.yoctoproject.org/listinfo/yocto" target="_top">yocto</a> or
                <a class="ulink" href="http://lists.linuxtogo.org/cgi-bin/mailman/listinfo/openembedded-devel" target="_top">openembedded-devel</a>
                mailing lists.</p></li></ul></div><p>      
    </p><p>  
        When you send a patch, be sure to include a "Signed-off-by:"
        line in the same style as required by the Linux kernel. 
        Adding this line signifies that you, the submitter, have agreed to the Developer's Certificate of Origin 1.1
        as follows:
        </p><pre class="literallayout">
     Developer's Certificate of Origin 1.1

     By making a contribution to this project, I certify that:

     (a) The contribution was created in whole or in part by me and I
         have the right to submit it under the open source license
         indicated in the file; or

     (b) The contribution is based upon previous work that, to the best
         of my knowledge, is covered under an appropriate open source
         license and I have the right under that license to submit that
         work with modifications, whether created in whole or in part
         by me, under the same open source license (unless I am
         permitted to submit under a different license), as indicated
         in the file; or

     (c) The contribution was provided directly to me by some other
         person who certified (a), (b) or (c) and I have not modified
         it.

     (d) I understand and agree that this project and the contribution
         are public and that a record of the contribution (including all
         personal information I submit with it, including my sign-off) is
         maintained indefinitely and may be redistributed consistent with
         this project or the open source license(s) involved.
        </pre><p>
    </p><p>
        In a collaborative environment, it is necessary to have some sort of standard 
        or method through which you submit changes.  
        Otherwise, things could get quite chaotic.
        One general practice to follow is to make small, controlled changes.
        Keeping changes small and isolated aids review, makes merging/rebasing easier
        and keeps the change history clean when anyone needs to refer to it in future.
    </p><p>
        When you make a commit, you must follow certain standards established by the
        OpenEmbedded and Yocto Project development teams.
        For each commit, you must provide a single-line summary of the change and you
        should almost always provide a more detailed description of what you did (i.e.
        the body of the commit message).
        The only exceptions for not providing a detailed description would be if your 
        change is a simple, self-explanatory change that needs no description.
        Here are the guidelines for composing a commit message:
        </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>Provide a single-line, short summary of the change.
                This summary is typically viewable in the "shortlist" of changes.
                Thus, providing something short and descriptive that gives the reader 
                a summary of the change is useful when viewing a list of many commits.
                This should be prefixed by the recipe name (if changing a recipe), or
                else the short form path to the file being changed.
                </p></li><li class="listitem"><p>For the body of the commit message, provide detailed information
                that describes what you changed, why you made the change, and the approach
                you used. It may also be helpful if you mention how you tested the change.
                Provide as much detail as you can in the body of the commit message.
                </p></li><li class="listitem"><p>If the change addresses a specific bug or issue that is 
                associated with a bug-tracking ID, include a reference to that ID in
                your detailed description.
                For example, the Yocto Project uses a specific convention for bug
                references - any commit that addresses a specific bug should include the
                bug ID in the description (typically at the beginning) as follows:
                </p><pre class="literallayout">
     [YOCTO #&lt;bug-id&gt;]

     &lt;detailed description of change&gt;
                </pre></li></ul></div><p>
    </p><p>
        You can find more guidance on creating well-formed commit messages at this OpenEmbedded 
        wiki page:
        <a class="ulink" href="http://www.openembedded.org/wiki/Commit_Patch_Message_Guidelines" target="_top">http://www.openembedded.org/wiki/Commit_Patch_Message_Guidelines</a>.
    </p><p>
        Following are general instructions for both pushing changes upstream and for submitting 
        changes as patches.
    </p><div class="section" title="3.9.1. Using Scripts to Push a Change Upstream and Request a Pull"><div class="titlepage"><div><div><h3 class="title"><a id="pushing-a-change-upstream"></a>3.9.1. Using Scripts to Push a Change Upstream and Request a Pull</h3></div></div></div><p>
            The basic flow for pushing a change to an upstream "contrib" Git repository is as follows:
            </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>Make your changes in your local Git repository.</p></li><li class="listitem"><p>Stage your changes by using the <code class="filename">git add</code>
                    command on each file you changed.</p></li><li class="listitem"><p>Commit the change by using the <code class="filename">git commit</code>
                    command and push it to the "contrib" repository.  
                    Be sure to provide a commit message that follows the project’s commit message standards
                    as described earlier.</p></li><li class="listitem"><p>Notify the maintainer that you have pushed a change by making a pull 
                    request.
                    The Yocto Project provides two scripts that conveniently let you generate and send
                    pull requests to the Yocto Project.
                    These scripts are <code class="filename">create-pull-request</code> and 
                    <code class="filename">send-pull-request</code>.
                    You can find these scripts in the <code class="filename">scripts</code> directory of the 
                    Yocto Project file structure.</p><p>Using these scripts correctly formats the requests without introducing any
                    whitespace or HTML formatting.
                    The maintainer that receives your patches needs to be able to save and apply them 
                    directly from your emails.
                    Using these scripts is the preferred method for sending patches.</p><p>For help on using these scripts, simply provide the 
                    <code class="filename">-h</code> argument as follows:
                    </p><pre class="literallayout">
     $ ~/poky/scripts/create-pull-request -h
     $ ~/poky/scripts/send-pull-request -h
                    </pre></li></ul></div><p>
        </p><p>            
            You can find general Git information on how to push a change upstream in the 
            <a class="ulink" href="http://book.git-scm.com/3_distributed_workflows.html" target="_top">Git Community Book</a>.
        </p></div><div class="section" title="3.9.2. Using Email to Submit a Patch"><div class="titlepage"><div><div><h3 class="title"><a id="submitting-a-patch"></a>3.9.2. Using Email to Submit a Patch</h3></div></div></div><p>
            You can submit patches without using the <code class="filename">create-pull-request</code> and 
            <code class="filename">send-pull-request</code> scripts described in the previous section.
            Keep in mind, the preferred method is to use the scripts, however.
        </p><p>
            Depending on the components changed, you need to submit the email to a specific
            mailing list.
            For some guidance on which mailing list to use, see the list in the 
            "<a class="link" href="#how-to-submit-a-change" title="3.9. How to Submit a Change">How to Submit a Change</a>" section
            earlier in this manual.
            For a description of the available mailing lists, see
            "<a class="link" href="#resources-mailinglist" target="_top">Mailing Lists</a>"
            section in the Yocto Project Reference Manual.
        </p><p>            
            Here is the general procedure on how to submit a patch through email without using the 
            scripts:
            </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>Make your changes in your local Git repository.</p></li><li class="listitem"><p>Stage your changes by using the <code class="filename">git add</code>
                    command on each file you changed.</p></li><li class="listitem"><p>Commit the change by using the 
                    <code class="filename">git commit --signoff</code> command.
                    Using the <code class="filename">--signoff</code> option identifies you as the person 
                    making the change and also satisfies the Developer's Certificate of 
                    Origin (DCO) shown earlier.</p><p>When you form a commit you must follow certain standards established by the 
                    Yocto Project development team. 
                    See the earlier section
                    "<a class="link" href="#how-to-submit-a-change" title="3.9. How to Submit a Change">How to Submit a Change</a>" 
                    for Yocto Project commit message standards.</p></li><li class="listitem"><p>Format the commit into an email message.
                    To format commits, use the <code class="filename">git format-patch</code> command.
                    When you provide the command, you must include a revision list or a number of patches
                    as part of the command.
                    For example, these two commands each take the most recent single commit and 
                    format it as an email message in the current directory:  
                    </p><pre class="literallayout">
     $ git format-patch -1
     $ git format-patch HEAD~
                    </pre><p>After the command is run, the current directory contains a 
                    numbered <code class="filename">.patch</code> file for the commit.</p><p>If you provide several commits as part of the command, 
                    the <code class="filename">git format-patch</code> command produces a numbered 
                    series of files in the current directory – one for each commit.
                    If you have more than one patch, you should also use the 
                    <code class="filename">--cover</code> option with the command, which generates a 
                    cover letter as the first "patch" in the series.  
                    You can then edit the cover letter to provide a description for 
                    the series of patches.
                    For information on the <code class="filename">git format-patch</code> command, 
                    see <code class="filename">GIT_FORMAT_PATCH(1)</code> displayed using the  
                    <code class="filename">man git-format-patch</code> command.</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>If you are or will be a frequent contributor to the Yocto Project
                    or to OpenEmbedded, you might consider requesting a contrib area and the 
                    necessary associated rights.</div></li><li class="listitem"><p>Import the files into your mail client by using the 
                    <code class="filename">git send-email</code> command.
                    </p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>In order to use <code class="filename">git send-email</code>, you must have the 
                    the proper Git packages installed.
                    For Ubuntu and Fedora the package is <code class="filename">git-email</code>.</div><p>The <code class="filename">git send-email</code> command sends email by using a local
                    or remote Mail Transport Agent (MTA) such as 
                    <code class="filename">msmtp</code>, <code class="filename">sendmail</code>, or through a direct
                    <code class="filename">smtp</code> configuration in your Git <code class="filename">config</code>
                    file.
                    If you are submitting patches through email only, it is very important
                    that you submit them without any whitespace or HTML formatting that 
                    either you or your mailer introduces.
                    The maintainer that receives your patches needs to be able to save and 
                    apply them directly from your emails.
                    A good way to verify that what you are sending will be applicable by the 
                    maintainer is to do a dry run and send them to yourself and then 
                    save and apply them as the maintainer would.</p><p>The <code class="filename">git send-email</code> command is the preferred method
                    for sending your patches since there is no risk of compromising whitespace
                    in the body of the message, which can occur when you use your own mail client.
                    The command also has several options that let you 
                    specify recipients and perform further editing of the email message.
                    For information on how to use the <code class="filename">git send-email</code> command,
                    use the <code class="filename">man git-send-email</code> command.</p></li></ul></div><p>
        </p></div></div></div>

    <div class="chapter" title="Chapter 4. Common Tasks"><div class="titlepage"><div><div><h2 class="title"><a id="extendpoky"></a>Chapter 4. Common Tasks</h2></div></div></div><div class="toc"><dl><dt><span class="section"><a href="#understanding-and-creating-layers">4.1. Understanding and Creating Layers</a></span></dt><dd><dl><dt><span class="section"><a href="#yocto-project-layers">4.1.1. Layers</a></span></dt><dt><span class="section"><a href="#creating-your-own-layer">4.1.2. Creating Your Own Layer</a></span></dt><dt><span class="section"><a href="#enabling-your-layer">4.1.3. Enabling Your Layer</a></span></dt><dt><span class="section"><a href="#using-bbappend-files">4.1.4. Using .bbappend Files</a></span></dt><dt><span class="section"><a href="#prioritizing-your-layer">4.1.5. Prioritizing Your Layer</a></span></dt><dt><span class="section"><a href="#managing-layers">4.1.6. Managing Layers</a></span></dt></dl></dd><dt><span class="section"><a href="#usingpoky-extend-customimage">4.2. Customizing Images</a></span></dt><dd><dl><dt><span class="section"><a href="#usingpoky-extend-customimage-custombb">4.2.1. Customizing Images Using Custom .bb Files</a></span></dt><dt><span class="section"><a href="#usingpoky-extend-customimage-customtasks">4.2.2. Customizing Images Using Custom Tasks</a></span></dt><dt><span class="section"><a href="#usingpoky-extend-customimage-imagefeatures">4.2.3. Customizing Images Using Custom <code class="filename">IMAGE_FEATURES</code> and 
                <code class="filename">EXTRA_IMAGE_FEATURES</code></a></span></dt><dt><span class="section"><a href="#usingpoky-extend-customimage-localconf">4.2.4. Customizing Images Using <code class="filename">local.conf</code></a></span></dt></dl></dd><dt><span class="section"><a href="#usingpoky-extend-addpkg">4.3. Adding a Package</a></span></dt><dd><dl><dt><span class="section"><a href="#usingpoky-extend-addpkg-singlec">4.3.1. Single .c File Package (Hello World!)</a></span></dt><dt><span class="section"><a href="#usingpoky-extend-addpkg-autotools">4.3.2. Autotooled Package</a></span></dt><dt><span class="section"><a href="#usingpoky-extend-addpkg-makefile">4.3.3. Makefile-Based Package</a></span></dt><dt><span class="section"><a href="#splitting-an-application-into-multiple-packages">4.3.4. Splitting an Application into Multiple Packages</a></span></dt><dt><span class="section"><a href="#including-static-library-files">4.3.5. Including Static Library Files</a></span></dt><dt><span class="section"><a href="#usingpoky-extend-addpkg-postinstalls">4.3.6. Post Install Scripts</a></span></dt></dl></dd><dt><span class="section"><a href="#platdev-newmachine">4.4. Adding a New Machine</a></span></dt><dd><dl><dt><span class="section"><a href="#platdev-newmachine-conffile">4.4.1. Adding the Machine Configuration File</a></span></dt><dt><span class="section"><a href="#platdev-newmachine-kernel">4.4.2. Adding a Kernel for the Machine</a></span></dt><dt><span class="section"><a href="#platdev-newmachine-formfactor">4.4.3. Adding a Formfactor Configuration File</a></span></dt></dl></dd><dt><span class="section"><a href="#building-multiple-architecture-libraries-into-one-image">4.5. Combining Multiple Versions of Library Files into One Image</a></span></dt><dd><dl><dt><span class="section"><a href="#preparing-to-use-multilib">4.5.1. Preparing to use Multilib</a></span></dt><dt><span class="section"><a href="#using-multilib">4.5.2. Using Multilib</a></span></dt><dt><span class="section"><a href="#additional-implementation-details">4.5.3. Additional Implementation Details</a></span></dt></dl></dd><dt><span class="section"><a href="#configuring-the-kernel">4.6. Configuring the Kernel</a></span></dt><dd><dl><dt><span class="section"><a href="#using-menuconfig">4.6.1. Using  <code class="filename">menuconfig</code></a></span></dt><dt><span class="section"><a href="#creating-config-fragments">4.6.2. Creating Configuration Fragments</a></span></dt><dt><span class="section"><a href="#fine-tuning-the-kernel-configuration-file">4.6.3. Fine-tuning the Kernel Configuration File</a></span></dt></dl></dd><dt><span class="section"><a href="#usingpoky-changes-updatingimages">4.7. Updating Existing Images</a></span></dt><dt><span class="section"><a href="#usingpoky-changes-prbump">4.8. Incrementing a Package Revision Number</a></span></dt><dt><span class="section"><a href="#usingpoky-configuring-DISTRO_PN_ALIAS">4.9. Handling a Package Name Alias</a></span></dt><dt><span class="section"><a href="#building-software-from-an-external-source">4.10. Building Software from an External Source</a></span></dt><dt><span class="section"><a href="#excluding-recipes-from-the-build">4.11. Excluding Recipes From the Build</a></span></dt><dt><span class="section"><a href="#platdev-appdev-srcrev">4.12. Using an External SCM</a></span></dt><dt><span class="section"><a href="#platdev-gdb-remotedebug">4.13. Debugging With the GNU Project Debugger (GDB) Remotely</a></span></dt><dd><dl><dt><span class="section"><a href="#platdev-gdb-remotedebug-launch-gdbserver">4.13.1. Launching Gdbserver on the Target</a></span></dt><dt><span class="section"><a href="#platdev-gdb-remotedebug-launch-gdb">4.13.2. Launching GDB on the Host Computer</a></span></dt></dl></dd><dt><span class="section"><a href="#platdev-oprofile">4.14. Profiling with OProfile</a></span></dt><dd><dl><dt><span class="section"><a href="#platdev-oprofile-target">4.14.1. Profiling on the Target</a></span></dt><dt><span class="section"><a href="#platdev-oprofile-oprofileui">4.14.2. Using OProfileUI</a></span></dt></dl></dd></dl></div><p>
        This chapter describes standard tasks such as adding new
        software packages, extending or customizing images, and porting work to
        new hardware (adding a new machine). 
        The chapter also describes how to combine multiple 
        versions of library files into a single image, how to handle a package name alias, and
        gives advice about how to make changes to the Yocto Project to achieve the best results.
    </p><div class="section" title="4.1. Understanding and Creating Layers"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="understanding-and-creating-layers"></a>4.1. Understanding and Creating Layers</h2></div></div></div><p>
            The OpenEmbedded build system supports organizing <a class="link" href="#metadata">metadata</a> 
            into multiple layers. 
            Layers allow you to isolate different types of customizations from each other.
            You might find it tempting to keep everything in one layer when working on a single project.
            However, the more modular you organize your metadata, the easier it is to cope with future changes.
        </p><p>
            To illustrate how layers are used to keep things modular, consider machine customizations.
            These types of customizations typically reside in a BSP Layer.
            Furthermore, the machine customizations should be isolated from recipes and metadata that support 
            a new GUI environment, for example. 
            This situation gives you a couple a layers: one for the machine configurations, and one for the 
            GUI environment.
            It is important to understand, however, that the BSP layer can still make machine-specific 
            additions to recipes within the GUI environment layer without polluting the GUI layer itself 
            with those machine-specific changes. 
            You can accomplish this through a recipe that is a BitBake append 
            (<code class="filename">.bbappend</code>) file, which is described later in this section.
        </p><p>
        </p><div class="section" title="4.1.1. Layers"><div class="titlepage"><div><div><h3 class="title"><a id="yocto-project-layers"></a>4.1.1. Layers</h3></div></div></div><p>
                The source directory contains several layers right out of the box.
                You can easily identify a layer in the source directory by its folder name.
                Folders that are layers begin with the string <code class="filename">meta</code>.
                For example, when you set up the <a class="link" href="#source-directory">source directory</a>
                structure, you will see several layers: <code class="filename">meta</code>, <code class="filename">meta-demoapps</code>,
                <code class="filename">meta-skeleton</code>, and <code class="filename">meta-yocto</code>.
                Each of these folders is a layer.
            </p><p>
                Furthermore, if you set up a local copy of the <code class="filename">meta-intel</code> Git repository
                and then explore that folder, you will discover many BSP layers within the 
                <code class="filename">meta-intel</code> layer.
                For more information on BSP layers, see the 
                "<a class="link" href="#bsp-layers" target="_top">BSP Layers</a>"
                section in the Yocto Project Board Support Package (BSP) Developer's Guide.
            </p></div><div class="section" title="4.1.2. Creating Your Own Layer"><div class="titlepage"><div><div><h3 class="title"><a id="creating-your-own-layer"></a>4.1.2. Creating Your Own Layer</h3></div></div></div><p>
                It is very easy to create your own layer to use with the OpenEmbedded build system.
                Follow these general steps to create your layer:
                </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p><span class="emphasis"><em>Check Existing Layers:</em></span> Before creating a new layer, 
                        you should be sure someone has not already created a layer containing the metadata 
                        you need.
                        You can see the
                        <a class="ulink" href="http://www.openembedded.org/wiki/LayerIndex" target="_top"><code class="filename">LayerIndex</code></a>
                        for a list of layers from the OpenEmbedded community that can be used in the 
                        Yocto Project.</p></li><li class="listitem"><p><span class="emphasis"><em>Create a Directory:</em></span> Create the directory 
                        for your layer.
                        Traditionally, prepend the name of the folder with the string
                        <code class="filename">meta</code>.
                        For example:
                        </p><pre class="literallayout">
     meta-mylayer
     meta-GUI_xyz
     meta-mymachine
                        </pre></li><li class="listitem"><p><span class="emphasis"><em>Create a Layer Configuration File:</em></span> Inside your new
                       layer folder, you need to create a <code class="filename">conf/layer.conf</code> file.
                       It is easiest to take an existing layer configuration file and copy that to your 
                       layer's <code class="filename">conf</code> directory and then modify the file as needed.</p><p>The <code class="filename">meta-yocto/conf/layer.conf</code> file demonstrates the 
                       required syntax:
                       </p><pre class="literallayout">
     # We have a conf and classes directory, add to BBPATH
     BBPATH := "${LAYERDIR}:${BBPATH}"

     # We have recipes-* directories, add to BBFILES
     BBFILES := "${BBFILES} ${LAYERDIR}/recipes-*/*/*.bb \
                 ${LAYERDIR}/recipes-*/*/*.bbappend"

     BBFILE_COLLECTIONS += "yocto"
     BBFILE_PATTERN_yocto := "^${LAYERDIR}/"
     BBFILE_PRIORITY_yocto = "5" 
                        </pre><p>In the previous example, the recipes for the layers are added to 
                        <code class="filename"><a class="link" href="#var-BBFILES" target="_top">BBFILES</a></code>. 
                        The 
                        <code class="filename"><a class="link" href="#var-BBFILE_COLLECTIONS" target="_top">BBFILE_COLLECTIONS</a></code>
                        variable is then appended with the layer name. 
                        The 
                        <code class="filename"><a class="link" href="#var-BBFILE_PATTERN" target="_top">BBFILE_PATTERN</a></code> 
                        variable is set to a regular expression and is used to match files
                        from <code class="filename">BBFILES</code> into a particular layer.
                        In this case, immediate expansion of 
                        <code class="filename"><a class="link" href="#var-LAYERDIR" target="_top">LAYERDIR</a></code> 
                        sets <code class="filename">BBFILE_PATTERN</code> to the layer's path.
                        The 
                        <code class="filename"><a class="link" href="#var-BBFILE_PRIORITY" target="_top">BBFILE_PRIORITY</a></code> 
                        variable then assigns a priority to the layer. 
                        Applying priorities is useful in situations where the same package might appear in multiple
                        layers and allows you to choose what layer should take precedence.</p><p>Note the use of the 
                        <code class="filename"><a class="link" href="#var-LAYERDIR" target="_top">LAYERDIR</a></code> 
                        variable with the immediate expansion operator.
                        The <code class="filename">LAYERDIR</code> variable expands to the directory of the current layer and
                        requires the immediate expansion operator so that BitBake does not wait to expand the variable 
                        when it's parsing a different directory.</p><p>Through the use of the <code class="filename">BBPATH</code> variable,
                        BitBake locates <code class="filename">.bbclass</code> files, configuration
                        files, and files that are included with <code class="filename">include</code> 
                        and <code class="filename">require</code> statements. 
                        For these cases, BitBake uses the first file with the matching name found in 
                        <code class="filename">BBPATH</code>.
                        This is similar to the way the <code class="filename">PATH</code> variable is used for binaries. 
                        We recommend, therefore, that you use unique <code class="filename">.bbclass</code>
                        and configuration file names in your custom layer.</p></li><li class="listitem"><p><span class="emphasis"><em>Add Content:</em></span> Depending on the type of layer, 
                        add the content.
                        If the layer adds support for a machine, add the machine configuration in 
                        a <code class="filename">conf/machine/</code> file within the layer.
                        If the layer adds distro policy, add the distro configuration in a
                        <code class="filename">conf/distro/</code> file with the layer.
                        If the layer introduces new recipes, put the recipes you need in 
                        <code class="filename">recipes-*</code> subdirectories within the layer.</p></li></ol></div><p>
            </p><p>
                To create layers that are easier to maintain, you should consider the following:
                </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>Avoid "overlaying" entire recipes from other layers in your 
                        configuration.
                        In other words, don't copy an entire recipe into your layer and then modify it.
                        Use <code class="filename">.bbappend</code> files to override the parts of the 
                        recipe you need to modify.</p></li><li class="listitem"><p>Avoid duplicating include files.
                        Use <code class="filename">.bbappend</code> files for each recipe that uses an include 
                        file.
                        Or, if you are introducing a new recipe that requires the included file, use the 
                        path relative to the original layer directory to refer to the file.
                        For example, use <code class="filename">require recipes-core/somepackage/somefile.inc</code>
                        instead of <code class="filename">require somefile.inc</code>. 
                        If you're finding you have to overlay the include file, it could indicate a 
                        deficiency in the include file in the layer to which it originally belongs.
                        If this is the case, you need to address that deficiency instead of overlaying
                        the include file.
                        For example, consider how Qt 4 database support plugins are configured.
                        The source directory does not have 
                        MySQL or PostgreSQL, however OpenEmbedded's
                        layer <code class="filename">meta-oe</code> does.
                        Consequently, <code class="filename">meta-oe</code> uses <code class="filename">.bbappend</code>
                        files to modify the <code class="filename">QT_SQL_DRIVER_FLAGS</code> variable to enable 
                        the appropriate plugins. 
                        This variable was added to the <code class="filename">qt4.inc</code> include file in 
                        the source directory specifically to allow the <code class="filename">meta-oe</code> layer
                        to be able to control which plugins are built.</p></li></ul></div><p> 
            </p><p>
                We also recommend the following:
                </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>Store custom layers in a Git repository that uses the 
                        <code class="filename">meta-&lt;layer_name&gt;</code> format.</p></li><li class="listitem"><p>Clone the repository alongside other <code class="filename">meta</code>
                        directories in the 
                        <a class="link" href="#source-directory">source directory</a>.</p></li></ul></div><p>
                 Following these recommendations keeps your source directory and 
                 its configuration entirely inside the Yocto Project's core base.
            </p></div><div class="section" title="4.1.3. Enabling Your Layer"><div class="titlepage"><div><div><h3 class="title"><a id="enabling-your-layer"></a>4.1.3. Enabling Your Layer</h3></div></div></div><p>
                Before the OpenEmbedded build system can use your new layer, you need to enable it.
                To enable your layer, simply add your layer's path to the 
                <code class="filename"><a class="link" href="#var-BBLAYERS" target="_top">BBLAYERS</a></code> 
                variable in your <code class="filename">conf/bblayers.conf</code> file, which is found in the 
                <a class="link" href="#build-directory">build directory</a>. 
                The following example shows how to enable a layer named <code class="filename">meta-mylayer</code>:
                </p><pre class="literallayout">
     LCONF_VERSION = "1"

     BBFILES ?= ""
     BBLAYERS = " \
       /path/to/poky/meta \
       /path/to/poky/meta-yocto \
       /path/to/poky/meta-mylayer \
       "
                </pre><p>
            </p><p>
                BitBake parses each <code class="filename">conf/layer.conf</code> file as specified in the 
                <code class="filename">BBLAYERS</code> variable within the <code class="filename">conf/bblayers.conf</code>
                file.
                During the processing of each <code class="filename">conf/layer.conf</code> file, BitBake adds the 
                recipes, classes and configurations contained within the particular layer to the source
                directory.
            </p></div><div class="section" title="4.1.4. Using .bbappend Files"><div class="titlepage"><div><div><h3 class="title"><a id="using-bbappend-files"></a>4.1.4. Using .bbappend Files</h3></div></div></div><p>
                Recipes used to append metadata to other recipes are called BitBake append files.
                BitBake append files use the <code class="filename">.bbappend</code> file type suffix, while  
                underlying recipes to which metadata is being appended use the 
                <code class="filename">.bb</code> file type suffix.
            </p><p>
                A <code class="filename">.bbappend</code> file allows your layer to make additions or 
                changes to the content of another layer's recipe without having to copy the other 
                recipe into your layer.
                Your <code class="filename">.bbappend</code> file resides in your layer, while the underlying 
                <code class="filename">.bb</code> recipe file to which you are appending metadata
                resides in a different layer.
            </p><p>
                Append files files must have the same name as the underlying recipe.
                For example, the append file <code class="filename">someapp_1.3.bbappend</code> must 
                apply to <code class="filename">someapp_1.3.bb</code>.
                This means the original recipe and append file names are version number specific.
                If the underlying recipe is renamed to update to a newer version, the 
                corresponding <code class="filename">.bbappend</code> file must be renamed as well.
                During the build process, BitBake displays an error on starting if it detects a 
                <code class="filename">.bbappend</code> file that does not have an underlying recipe 
                with a matching name.
            </p><p>
                Being able to append information to an existing recipe not only avoids duplication, 
                but also automatically applies recipe changes in a different layer to your layer.
                If you were copying recipes, you would have to manually merge changes as they occur.
            </p><p>
                As an example, consider the main formfactor recipe and a corresponding formfactor 
                append file both from the 
                <a class="link" href="#source-directory">source directory</a>.
                Here is the main formfactor recipe, which is named <code class="filename">formfactor_0.0.bb</code> and  
                located in the meta layer at <code class="filename">meta/recipes-bsp/formfactor</code>:
                </p><pre class="literallayout">
     DESCRIPTION = "Device formfactor information"
     SECTION = "base"
     LICENSE = "MIT"
     LIC_FILES_CHKSUM = "file://${COREBASE}/LICENSE;md5=3f40d7994397109285ec7b81fdeb3b58 \
                         file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420"
     PR = "r20"

     SRC_URI = "file://config file://machconfig"
     S = "${WORKDIR}"

     PACKAGE_ARCH = "${MACHINE_ARCH}"
     INHIBIT_DEFAULT_DEPS = "1"

     do_install() {
     	# Only install file if it has a contents
             install -d ${D}${sysconfdir}/formfactor/
             install -m 0644 ${S}/config ${D}${sysconfdir}/formfactor/
     	if [ -s "${S}/machconfig" ]; then
     	        install -m 0644 ${S}/machconfig ${D}${sysconfdir}/formfactor/
     	fi
     }
                </pre><p>
                Here is the append file, which is named <code class="filename">formfactor_0.0.bbappend</code> and is from the 
                Crown Bay BSP Layer named <code class="filename">meta-intel/meta-crownbay</code>.
                The file is in <code class="filename">recipes-bsp/formfactor</code>:
                </p><pre class="literallayout">
     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
 
     PRINC = "1"
                </pre><p>
                This example adds or overrides files in 
                <a class="link" href="#var-SRC_URI" target="_top"><code class="filename">SRC_URI</code></a>
                within a <code class="filename">.bbappend</code> by extending the path BitBake uses to search for files. 
                The most reliable way to do this is by prepending the 
                <code class="filename">FILESEXTRAPATHS</code> variable.
                For example, if you have your files in a directory that is named the same as your package 
                (<a class="link" href="#var-PN" target="_top"><code class="filename">PN</code></a>),
                you can add this directory by adding the following to your <code class="filename">.bbappend</code> file:
                </p><pre class="literallayout">
     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
                </pre><p>
                Using the immediate expansion assignment operator <code class="filename">:=</code> is important because 
                of the reference to <code class="filename">THISDIR</code>.
                The trailing colon character is important as it ensures that items in the list remain 
                colon-separated.
                </p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3>BitBake automatically defines the <code class="filename">THISDIR</code> variable.
                    You should never set this variable yourself.
                    Using <code class="filename">_prepend</code> ensures your path will be searched prior to other 
                    paths in the final list.
                </div><p>
            </p><p>
                For another example on how to use a <code class="filename">.bbappend</code> file, see the 
                "<a class="link" href="#changing-recipes-kernel" title="A.5.2.4. Changing  recipes-kernel">Changing <code class="filename">recipes-kernel</code></a>"
                section.
            </p></div><div class="section" title="4.1.5. Prioritizing Your Layer"><div class="titlepage"><div><div><h3 class="title"><a id="prioritizing-your-layer"></a>4.1.5. Prioritizing Your Layer</h3></div></div></div><p>
                Each layer is assigned a priority value.
                Priority values control which layer takes precedence if there are recipe files with 
                the same name in multiple layers.
                For these cases, the recipe file from the layer with a higher priority number taking precedence.
                Priority values also affect the order in which multiple <code class="filename">.bbappend</code> files 
                for the same recipe are applied. 
                You can either specify the priority manually, or allow the build system to calculate it
                based on the layer's dependencies.
            </p><p>
                To specify the layer's priority manually, use the 
                <a class="link" href="#var-BBFILE_PRIORITY" target="_top"><code class="filename">BBFILE_PRIORITY</code></a>
                variable.
                For example:
                </p><pre class="literallayout">
     BBFILE_PRIORITY := "1"
                </pre><p>
            </p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>It is possible for a recipe with a lower version number 
                <a class="link" href="#var-PV" target="_top"><code class="filename">PV</code></a>
                in a layer that has a higher priority to take precedence.</p><p>Also, the layer priority does not currently affect the precedence order of 
                <code class="filename">.conf</code> or <code class="filename">.bbclass</code> files.
                Future versions of BitBake might address this.</p></div></div><div class="section" title="4.1.6. Managing Layers"><div class="titlepage"><div><div><h3 class="title"><a id="managing-layers"></a>4.1.6. Managing Layers</h3></div></div></div><p>
                You can use the BitBake layer management tool to provide a view into the structure of 
                recipes across a multi-layer project.
                Being able to generate output that reports on configured layers with their paths and 
                priorities and on <code class="filename">.bbappend</code> files and their applicable recipes
                can help to reveal potential problems.
            </p><p>
                Use the following form when running the layer management tool.
                </p><pre class="literallayout">
     $ bitbake-layers &lt;command&gt; [arguments]
                </pre><p>
                The following list describes the available commands:
                </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><code class="filename"><span class="emphasis"><em>help:</em></span></code>
                        Displays general help or help on a specified command.</p></li><li class="listitem"><p><code class="filename"><span class="emphasis"><em>show-layers:</em></span></code>
                        Show the current configured layers.</p></li><li class="listitem"><p><code class="filename"><span class="emphasis"><em>show-recipes:</em></span></code>
                        Lists available recipes and the layers that provide them.  
                        </p></li><li class="listitem"><p><code class="filename"><span class="emphasis"><em>show-overlayed:</em></span></code>
                        Lists overlayed recipes.  
                        A recipe is overlayed when a recipe with the same name exists in another layer 
                        that has a higher layer priority.
                        </p></li><li class="listitem"><p><code class="filename"><span class="emphasis"><em>show-appends:</em></span></code>
                        Lists <code class="filename">.bbappend</code> files and the recipe files to which
                        they apply.</p></li><li class="listitem"><p><code class="filename"><span class="emphasis"><em>flatten:</em></span></code>
                        Flattens the layer configuration into a separate output directory.
                        Flattening your layer configuration builds a "flattened" directory that contains
                        the contents of all layers, with any overlayed recipes removed and any
                        <code class="filename">.bbappend</code> files appended to the corresponding recipes.
                        You might have to perform some manual cleanup of the flattened layer as follows:
                        </p><div class="itemizedlist"><ul class="itemizedlist" type="circle"><li class="listitem"><p>Non-recipe files (such as patches) are overwritten.
                                The flatten command shows a warning for these files.</p></li><li class="listitem"><p>Anything beyond the normal layer setup has been added to 
                                the <code class="filename">layer.conf</code> file.
                                Only the lowest priority layer's <code class="filename">layer.conf</code> is used.
                                </p></li><li class="listitem"><p>Overridden and appended items from <code class="filename">.bbappend</code>
                                files need to be cleaned up.
                                The contents of each <code class="filename">.bbappend</code> end up in the 
                                flattened recipe.
                                However, if there are appended or changed variable values, you need to tidy 
                                these up yourself.
                                Consider the following example.
                                Here, the <code class="filename">bitbake-layers</code> command adds the line
                                <code class="filename">#### bbappended ...</code> so that you know where the following
                                lines originate:
                                </p><pre class="literallayout">
     ...
     DESCRIPTION = "A useful utility"
     ...
     EXTRA_OECONF = "--enable-something"
     ...

     #### bbappended from meta-anotherlayer ####

     DESCRIPTION = "Customized utility"
     EXTRA_OECONF += "--enable-somethingelse"
                                </pre><p>
                                Ideally, you would tidy up these utilities as follows:
                                </p><pre class="literallayout">
     ...
     DESCRIPTION = "Customized utility"
     ...
     EXTRA_OECONF = "--enable-something --enable-somethingelse"
     ...
                                </pre></li></ul></div></li></ul></div><p>
            </p></div></div><div class="section" title="4.2. Customizing Images"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="usingpoky-extend-customimage"></a>4.2. Customizing Images</h2></div></div></div><p>
            You can customize images to satisfy particular requirements. 
            This section describes several methods and provides guidelines for each.
        </p><div class="section" title="4.2.1. Customizing Images Using Custom .bb Files"><div class="titlepage"><div><div><h3 class="title"><a id="usingpoky-extend-customimage-custombb"></a>4.2.1. Customizing Images Using Custom .bb Files</h3></div></div></div><p>
                One way to get additional software into an image is to create a custom image. 
                The following example shows the form for the two lines you need:
                </p><pre class="literallayout">
     IMAGE_INSTALL = "task-core-x11-base package1 package2"

     inherit core-image
                </pre><p>
            </p><p>
                By creating a custom image, a developer has total control
                over the contents of the image. 
                It is important to use the correct names of packages in the 
                <code class="filename"><a class="link" href="#var-IMAGE_INSTALL" target="_top">IMAGE_INSTALL</a></code> 
                variable. 
                You must use the OpenEmbedded notation and not the Debian notation for the names 
                (e.g. <code class="filename">eglibc-dev</code> instead of <code class="filename">libc6-dev</code>).
            </p><p>
                The other method for creating a custom image is to base it on an existing image. 
                For example, if you want to create an image based on <code class="filename">core-image-sato</code>
                but add the additional package <code class="filename">strace</code> to the image, 
                copy the <code class="filename">meta/recipes-sato/images/core-image-sato.bb</code> to a 
                new <code class="filename">.bb</code> and add the following line to the end of the copy:
                </p><pre class="literallayout">
     IMAGE_INSTALL += "strace"
                </pre><p>
            </p></div><div class="section" title="4.2.2. Customizing Images Using Custom Tasks"><div class="titlepage"><div><div><h3 class="title"><a id="usingpoky-extend-customimage-customtasks"></a>4.2.2. Customizing Images Using Custom Tasks</h3></div></div></div><p>
                For complex custom images, the best approach is to create a custom task package
                that is used to build the image or images. 
                A good example of a tasks package is 
                <code class="filename">meta/recipes-core/tasks/task-core-boot.bb</code>
                The 
                <code class="filename"><a class="link" href="#var-PACKAGES" target="_top">PACKAGES</a></code> 
                variable lists the task packages to build along with the complementary
                <code class="filename">-dbg</code> and <code class="filename">-dev</code> packages. 
                For each package added, you can use 
                <code class="filename"><a class="link" href="#var-RDEPENDS" target="_top">RDEPENDS</a></code>
                and 
                <code class="filename"><a class="link" href="#var-RRECOMMENDS" target="_top">RRECOMMENDS</a></code> 
                entries to provide a list of packages the parent task package should contain. 
                Following is an example:
                </p><pre class="literallayout">
     DESCRIPTION = "My Custom Tasks"

     PACKAGES = "\
         task-custom-apps \
         task-custom-apps-dbg \
         task-custom-apps-dev \
         task-custom-tools \
         task-custom-tools-dbg \
         task-custom-tools-dev \
         "

     RDEPENDS_task-custom-apps = "\
         dropbear \
         portmap \
         psplash"

     RDEPENDS_task-custom-tools = "\
         oprofile \
         oprofileui-server \
         lttng-control \
         lttng-viewer"

     RRECOMMENDS_task-custom-tools = "\
         kernel-module-oprofile"
                </pre><p>
            </p><p>
                In the previous example, two task packages are created with their dependencies and their
                recommended package dependencies listed: <code class="filename">task-custom-apps</code>, and 
                <code class="filename">task-custom-tools</code>. 
                To build an image using these task packages, you need to add 
                <code class="filename">task-custom-apps</code> and/or 
                <code class="filename">task-custom-tools</code> to 
                <code class="filename"><a class="link" href="#var-IMAGE_INSTALL" target="_top">IMAGE_INSTALL</a></code>.
                For other forms of image dependencies see the other areas of this section.
            </p></div><div class="section" title="4.2.3. Customizing Images Using Custom IMAGE_FEATURES and EXTRA_IMAGE_FEATURES"><div class="titlepage"><div><div><h3 class="title"><a id="usingpoky-extend-customimage-imagefeatures"></a>4.2.3. Customizing Images Using Custom <code class="filename">IMAGE_FEATURES</code> and 
                <code class="filename">EXTRA_IMAGE_FEATURES</code></h3></div></div></div><p>
                Ultimately users might want to add extra image features to the set by using the 
                <code class="filename"><a class="link" href="#var-IMAGE_FEATURES" target="_top">IMAGE_FEATURES</a></code>
                variable. 
                To create these features, the best reference is 
                <code class="filename">meta/classes/core-image.bbclass</code>, which shows how to achieve this. 
                In summary, the file looks at the contents of the 
                <code class="filename">IMAGE_FEATURES</code>
                variable and then maps that into a set of tasks or packages. 
                Based on this information the 
                <code class="filename"><a class="link" href="#var-IMAGE_INSTALL" target="_top"> IMAGE_INSTALL</a></code> 
                variable is generated automatically. 
                Users can add extra features by extending the class or creating a custom class for use 
                with specialized image <code class="filename">.bb</code> files.
                You can also add more features by configuring the 
                <code class="filename"><a class="link" href="#var-EXTRA_IMAGE_FEATURES" target="_top">EXTRA_IMAGE_FEATURES</a></code>
                variable in the <code class="filename">local.conf</code> file found in the source directory
                located in the build directory.
            </p><p>
                The Yocto Project ships with two SSH servers you can use in your images: 
                Dropbear and OpenSSH. 
                Dropbear is a minimal SSH server appropriate for resource-constrained environments,
                while OpenSSH is a well-known standard SSH server implementation.
                By default, the <code class="filename">core-image-sato</code> image is configured to use Dropbear.
                The <code class="filename">core-image-basic</code> and <code class="filename">core-image-lsb</code>
                images both include OpenSSH.
                The <code class="filename">core-image-minimal</code> image does not contain an SSH server.
                To change these defaults, edit the <code class="filename">IMAGE_FEATURES</code> variable
                so that it sets the image you are working with to include 
                <code class="filename">ssh-server-dropbear</code> or <code class="filename">ssh-server-openssh</code>.
            </p></div><div class="section" title="4.2.4. Customizing Images Using local.conf"><div class="titlepage"><div><div><h3 class="title"><a id="usingpoky-extend-customimage-localconf"></a>4.2.4. Customizing Images Using <code class="filename">local.conf</code></h3></div></div></div><p>
                It is possible to customize image contents by using variables from your
                local configuration in your <code class="filename">conf/local.conf</code> file. 
                Because it is limited to local use, this method generally only allows you to 
                add packages and is not as flexible as creating your own customized image.
                When you add packages using local variables this way, you need to realize that 
                these variable changes affect all images at the same time and might not be
                what you require.
            </p><p>
                The simplest way to add extra packages to all images is by using the 
                <code class="filename"><a class="link" href="#var-IMAGE_INSTALL" target="_top">IMAGE_INSTALL</a></code>
                variable with the <code class="filename">_append</code> operator:
                </p><pre class="literallayout">
     IMAGE_INSTALL_append = " strace"
                </pre><p>
                Use of the syntax is important.
                Specifically, the space between the quote and the package name, which is
                <code class="filename">strace</code> in this example.
                This space is required since the <code class="filename">_append</code>
                operator does not add the space.
            </p><p>
                Furthermore, you must use <code class="filename">_append</code> instead of the <code class="filename">+=</code> 
                operator if you want to avoid ordering issues. 
                The reason for this is because doing so unconditionally appends to the variable and 
                avoids ordering problems due to the variable being set in image recipes and 
                <code class="filename">.bbclass</code> files with operators like <code class="filename">?=</code>.
                Using <code class="filename">_append</code> ensures the operation takes affect.
            </p><p>
                As shown in its simplest use, <code class="filename">IMAGE_INSTALL_append</code> affects
                all images.
                It is possible to extend the syntax so that the variable applies to a specific image only.
                Here is an example:
                </p><pre class="literallayout">
     IMAGE_INSTALL_append_pn-core-image-minimal = " strace"
                </pre><p>
                This example adds <code class="filename">strace</code> to <code class="filename">core-image-minimal</code>
                only.
            </p><p>
                You can add packages using a similar approach through the  
                <code class="filename"><a class="link" href="#var-CORE_IMAGE_EXTRA_INSTALL" target="_top">CORE_IMAGE_EXTRA_INSTALL</a></code> 
                variable.
                If you use this variable, only <code class="filename">core-image-*</code> images are affected.
            </p></div></div><div class="section" title="4.3. Adding a Package"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="usingpoky-extend-addpkg"></a>4.3. Adding a Package</h2></div></div></div><p>
            To add a package you need to write a recipe for it. 
            Writing a recipe means creating a <code class="filename">.bb</code> file that sets some
            variables.
            For information on variables that are useful for recipes and for information about recipe naming
            issues, see the 
            "<a class="link" href="#ref-varlocality-recipe-required" target="_top">Required</a>" 
            section of the Yocto Project Reference Manual.
        </p><p>
            Before writing a recipe from scratch, it is often useful to check
            whether someone else has written one already. 
            OpenEmbedded is a good place to look as it has a wider scope and range of packages.
            Because the Yocto Project aims to be compatible with OpenEmbedded, most recipes 
            you find there should work for you.
        </p><p>
            For new packages, the simplest way to add a recipe is to base it on a similar
            pre-existing recipe. 
            The sections that follow provide some examples that show how to add standard 
            types of packages.
        </p><div class="section" title="4.3.1. Single .c File Package (Hello World!)"><div class="titlepage"><div><div><h3 class="title"><a id="usingpoky-extend-addpkg-singlec"></a>4.3.1. Single .c File Package (Hello World!)</h3></div></div></div><p>
                Building an application from a single file that is stored locally (e.g. under 
                <code class="filename">files/</code>) requires a recipe that has the file listed in 
                the 
                <code class="filename"><a class="link" href="#var-SRC_URI" target="_top">SRC_URI</a></code>
                variable. 
                Additionally, you need to manually write the <code class="filename">do_compile</code> and
                <code class="filename">do_install</code> tasks.
                The <code class="filename"><a class="link" href="#var-S" target="_top">S</a></code> 
                variable defines the 
                directory containing the source code, which is set to 
                <code class="filename"><a class="link" href="#var-WORKDIR" target="_top">
                WORKDIR</a></code> in this case - the directory BitBake uses for the build.
                </p><pre class="literallayout">
     DESCRIPTION = "Simple helloworld application"
     SECTION = "examples"
     LICENSE = "MIT"
     LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/MIT;md5=0835ade698e0bcf8506ecda2f7b4f302"
     PR = "r0"

     SRC_URI = "file://helloworld.c"

     S = "${WORKDIR}"

     do_compile() {
     	${CC} helloworld.c -o helloworld
     }

     do_install() {
     	install -d ${D}${bindir}
     	install -m 0755 helloworld ${D}${bindir}
     }
                </pre><p>
            </p><p>
                By default, the <code class="filename">helloworld</code>, <code class="filename">helloworld-dbg</code>,
                and <code class="filename">helloworld-dev</code> packages are built. 
                For information on how to customize the packaging process, see the
                "<a class="link" href="#splitting-an-application-into-multiple-packages" title="4.3.4. Splitting an Application into Multiple Packages">Splitting an Application
                into Multiple Packages</a>" section.
            </p></div><div class="section" title="4.3.2. Autotooled Package"><div class="titlepage"><div><div><h3 class="title"><a id="usingpoky-extend-addpkg-autotools"></a>4.3.2. Autotooled Package</h3></div></div></div><p>
                Applications that use Autotools such as <code class="filename">autoconf</code> and 
                <code class="filename">automake</code> require a recipe that has a source archive listed in 
                <code class="filename"><a class="link" href="#var-SRC_URI" target="_top">SRC_URI</a></code> and 
                also inherits Autotools, which instructs BitBake to use the
                <code class="filename">autotools.bbclass</code> file, which contains the definitions of all the steps
                needed to build an Autotool-based application.
                The result of the build is automatically packaged. 
                And, if the application uses NLS for localization, packages with local information are 
                generated (one package per language). 
                Following is one example: (<code class="filename">hello_2.3.bb</code>)
                </p><pre class="literallayout">
     DESCRIPTION = "GNU Helloworld application"
     SECTION = "examples"
     LICENSE = "GPLv2+"
     LIC_FILES_CHKSUM = "file://COPYING;md5=751419260aa954499f7abaabaa882bbe"
     PR = "r0"

     SRC_URI = "${GNU_MIRROR}/hello/hello-${</