path: root/documentation/dev-manual/dev-manual-start.xml

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

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

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

<para>
    This chapter provides procedures related to getting set up to use the
    Yocto Project.
    For a more front-to-end process that takes you from minimally preparing
    a build host through building an image, see the
    <ulink url='&YOCTO_DOCS_QS_URL;'>Yocto Project Quick Start</ulink>.
</para>

<section id='getting-setup'>
    <title>Getting Set Up</title>

    <para>
        Here is what you need to use the Yocto Project:
        <itemizedlist>
            <listitem><para><emphasis>Host System:</emphasis>  You should have a reasonably current
                Linux-based host system.
                You will have the best results with a recent release of Fedora,
                openSUSE, Debian, Ubuntu, or CentOS as these releases are frequently tested against the Yocto Project
                and officially supported.
                For a list of the distributions under validation and their status, see the
                "<ulink url='&YOCTO_DOCS_REF_URL;#detailed-supported-distros'>Supported Linux Distributions</ulink>" section
                in the Yocto Project Reference Manual and the wiki page at
                <ulink url='&YOCTO_WIKI_URL;/wiki/Distribution_Support'>Distribution Support</ulink>.</para>
                <para>
                You should also have about 50 Gbytes of free disk space for building images.
                </para></listitem>
            <listitem><para><emphasis>Packages:</emphasis>  The OpenEmbedded build system
                requires that certain packages exist on your development system (e.g. Python 2.7).
                See "<ulink url='&YOCTO_DOCS_QS_URL;#packages'>The Build Host Packages</ulink>"
                section in the Yocto Project Quick Start and the
                "<ulink url='&YOCTO_DOCS_REF_URL;#required-packages-for-the-host-development-system'>Required Packages for the Host Development System</ulink>"
                section in the Yocto Project Reference Manual for the exact
                package requirements and the installation commands to install
                them for the supported distributions.
                </para></listitem>
            <listitem id='local-yp-release'><para><emphasis>Yocto Project Release:</emphasis>
                You need a release of the Yocto Project locally installed on
                your development system.
                The documentation refers to this set of locally installed files
                as the <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>.
                You create your Source Directory by using
                <ulink url='&YOCTO_DOCS_REF_URL;#git'>Git</ulink> to clone a local copy
                of the upstream <filename>poky</filename> repository,
                or by downloading and unpacking a tarball of an official
                Yocto Project release.
                The preferred method is to create a clone of the repository.
                </para>
                <para>Working from a copy of the upstream repository allows you
                to contribute back into the Yocto Project or simply work with
                the latest software on a development branch.
                Because Git maintains and creates an upstream repository with
                a complete history of changes and you are working with a local
                clone of that repository, you have access to all the Yocto
                Project development branches and tag names used in the upstream
                repository.</para>
                <note>You can view the Yocto Project Source Repositories at
                    <ulink url='&YOCTO_GIT_URL;/cgit.cgi'></ulink>
                </note>
                <para>The following transcript shows how to clone the
                <filename>poky</filename> Git repository into the current
                working directory.
                The command creates the local repository in a directory
                named <filename>poky</filename>.
                For information on Git used within the Yocto Project, see
                the "<ulink url='&YOCTO_DOCS_REF_URL;#git'>Git</ulink>" section.
                <literallayout class='monospaced'>
     $ git clone git://git.yoctoproject.org/poky
     Cloning into 'poky'...
     remote: Counting objects: 226790, done.
     remote: Compressing objects: 100% (57465/57465), done.
     remote: Total 226790 (delta 165212), reused 225887 (delta 164327)
     Receiving objects: 100% (226790/226790), 100.98 MiB | 263 KiB/s, done.
     Resolving deltas: 100% (165212/165212), done.
                </literallayout></para>
                <para>For another example of how to set up your own local Git
                repositories, see this
                <ulink url='&YOCTO_WIKI_URL;/wiki/Transcript:_from_git_checkout_to_meta-intel_BSP'>
                wiki page</ulink>, which describes how to create local
                Git repositories for both
                <filename>poky</filename> and <filename>meta-intel</filename>.
                </para>
                <para>
                You can also get the Yocto Project Files by downloading
                Yocto Project releases from the
                <ulink url="&YOCTO_HOME_URL;">Yocto Project website</ulink>.
                From the website, you just click "Downloads" in the navigation
                pane to the left to display all Yocto Project downloads.
                Current and archived releases are available for download.
                Nightly and developmental builds are also maintained at
                <ulink url="&YOCTO_AB_NIGHTLY_URL;"></ulink>.
                One final site you can visit for information on Yocto Project
                releases is the
                <ulink url='&YOCTO_WIKI_URL;/wiki/Releases'>Releases</ulink>
                wiki.
                </para></listitem>
            <listitem id='local-kernel-files'><para><emphasis>Yocto Project Kernel:</emphasis>
                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 Linux Kernel" in the Yocto Project Source Repositories at
                <ulink url='&YOCTO_GIT_URL;/cgit.cgi'></ulink>.</para>
                <para>This setup can involve 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, which is usually named <filename>poky</filename>.</para>
                <para>As an example, the following transcript shows how to create the bare clone
                of the <filename>linux-yocto-3.19</filename> kernel and then create a copy of
                that clone.
                <note>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 <filename>clone</filename> command.
                Doing so can speed up the process.</note></para>
                <para>In the following example, the bare clone is named
                <filename>linux-yocto-3.19.git</filename>, while the
                copy is named <filename>my-linux-yocto-3.19-work</filename>:
                <literallayout class='monospaced'>
     $ git clone --bare git://git.yoctoproject.org/linux-yocto-3.19 linux-yocto-3.19.git
     Cloning into bare repository 'linux-yocto-3.19.git'...
     remote: Counting objects: 3983256, done.
     remote: Compressing objects: 100% (605006/605006), done.
     remote: Total 3983256 (delta 3352832), reused 3974503 (delta 3344079)
     Receiving objects: 100% (3983256/3983256), 843.66 MiB | 1.07 MiB/s, done.
     Resolving deltas: 100% (3352832/3352832), done.
     Checking connectivity... done.
                </literallayout></para>
                <para>Now create a clone of the bare clone just created:
                <literallayout class='monospaced'>
     $ git clone linux-yocto-3.19.git my-linux-yocto-3.19-work
     Cloning into 'my-linux-yocto-3.19-work'...
     done.
     Checking out files: 100% (48440/48440), done.
                </literallayout></para></listitem>
            <listitem id='meta-yocto-kernel-extras-repo'><para><emphasis>
                The <filename>meta-yocto-kernel-extras</filename> Git Repository</emphasis>:
                The <filename>meta-yocto-kernel-extras</filename> Git repository contains Metadata needed
                only if you are modifying and building the kernel image.
                In particular, it contains the kernel BitBake append (<filename>.bbappend</filename>)
                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.</para>
                <para>You can find the <filename>meta-yocto-kernel-extras</filename> Git Repository in the
                "Yocto Metadata Layers" area of the Yocto Project Source Repositories at
                <ulink url='&YOCTO_GIT_URL;/cgit.cgi'></ulink>.
                It is good practice to create this Git repository inside the Source Directory.</para>
                <para>Following is an example that creates the <filename>meta-yocto-kernel-extras</filename> Git
                repository inside the Source Directory, which is named <filename>poky</filename>
                in this case:
                <literallayout class='monospaced'>
     $ cd ~/poky
     $ git clone git://git.yoctoproject.org/meta-yocto-kernel-extras meta-yocto-kernel-extras
     Cloning into 'meta-yocto-kernel-extras'...
     remote: Counting objects: 727, done.
     remote: Compressing objects: 100% (452/452), done.
     remote: Total 727 (delta 260), reused 719 (delta 252)
     Receiving objects: 100% (727/727), 536.36 KiB | 240 KiB/s, done.
     Resolving deltas: 100% (260/260), done.
               </literallayout></para></listitem>
           <listitem><para id='supported-board-support-packages-(bsps)'><emphasis>Supported Board Support Packages (BSPs):</emphasis>
                The Yocto Project supports many BSPs, which are maintained in
                their own layers or in layers designed to contain several
                BSPs.
                To get an idea of machine support through BSP layers, you can
                look at the
                <ulink url='&YOCTO_RELEASE_DL_URL;/machines'>index of machines</ulink>
                for the release.</para>

                <para>The Yocto Project uses the following BSP layer naming
                scheme:
                <literallayout class='monospaced'>
     meta-<replaceable>bsp_name</replaceable>
                </literallayout>
                where <replaceable>bsp_name</replaceable> is the recognized
                BSP name.
                Here is an example:
                <literallayout class='monospaced'>
     meta-raspberrypi
                </literallayout>
                See the
                "<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>"
                section in the Yocto Project Board Support Package (BSP)
                Developer's Guide for more information on BSP Layers.</para>

                <para>A useful Git repository released with the Yocto
                Project is <filename>meta-intel</filename>, which is a
                parent layer that contains many supported
                <ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>.
                You can locate the <filename>meta-intel</filename> Git
                repository in the "Yocto Metadata Layers" area of the Yocto
                Project Source Repositories at
                <ulink url='&YOCTO_GIT_URL;/cgit.cgi'></ulink>.</para>

                <para>Using
                <ulink url='&YOCTO_DOCS_REF_URL;#git'>Git</ulink> to create a local clone of the
                upstream repository can be helpful if you are working with
                BSPs.
                Typically, you set up the <filename>meta-intel</filename>
                Git repository inside the Source Directory.
                For example, the following transcript shows the steps to clone
                <filename>meta-intel</filename>.
                <note>
                    Be sure to work in the <filename>meta-intel</filename>
                    branch that matches your
                    <ulink url='&YOCTO_DOCS_REF_URL;#source-directory'>Source Directory</ulink>
                    (i.e. <filename>poky</filename>) branch.
                    For example, if you have checked out the "master" branch
                    of <filename>poky</filename> and you are going to use
                    <filename>meta-intel</filename>, be sure to checkout the
                    "master" branch of <filename>meta-intel</filename>.
                </note>
                <literallayout class='monospaced'>
     $ cd ~/poky
     $ git clone git://git.yoctoproject.org/meta-intel.git
     Cloning into 'meta-intel'...
     remote: Counting objects: 11917, done.
     remote: Compressing objects: 100% (3842/3842), done.
     remote: Total 11917 (delta 6840), reused 11699 (delta 6622)
     Receiving objects: 100% (11917/11917), 2.92 MiB | 2.88 MiB/s, done.
     Resolving deltas: 100% (6840/6840), done.
     Checking connectivity... done.
                </literallayout></para>

                <para>The same
                <ulink url='&YOCTO_WIKI_URL;/wiki/Transcript:_from_git_checkout_to_meta-intel_BSP'>wiki page</ulink>
                referenced earlier covers how to set up the
                <filename>meta-intel</filename> Git repository.
                </para></listitem>
            <listitem><para><emphasis>Eclipse Yocto Plug-in:</emphasis>  If you are developing
                applications using the Eclipse Integrated Development Environment (IDE),
                you will need this plug-in.
                See the
                "<ulink url='&YOCTO_DOCS_SDK_URL;#sdk-appendix-latest-yp-eclipse-plug-in'>Using Eclipse</ulink>"
                section in the Yocto Project Software Development Kit (SDK)
                Developer's Guide for more information.</para></listitem>
        </itemizedlist>
    </para>
</section>

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

    <para>
        This section contains procedures related to locating and securing
        Yocto Project files.
        You establish and use these local files to work on projects.
        <note>
            For concepts and introductory information about Git as it is used
            in the Yocto Project, see the
            "<ulink url='&YOCTO_DOCS_REF_URL;#git'>Git</ulink>"
            section in the Yocto Project Reference Manual.
        </note>
    </para>

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

        <para>
            Follow these steps to create a local version of the
            upstream
            <ulink url='&YOCTO_DOCS_REF_URL;#poky'><filename>poky</filename></ulink>
            Git repository.
            <orderedlist>
                <listitem><para>
                    <emphasis>Set Your Directory:</emphasis>
                    Be in the directory where you want to create your local
                    copy of poky.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Clone the Repository:</emphasis>
                    The following command clones the repository and uses
                    the default name "poky" for your local repository:
                    <literallayout class='monospaced'>
     $ git clone git://git.yoctoproject.org/poky
     Cloning into 'poky'...
     remote: Counting objects: 367178, done.
     remote: Compressing objects: 100% (88161/88161), done.
     remote: Total 367178 (delta 272761), reused 366942 (delta 272525)
     Receiving objects: 100% (367178/367178), 133.26 MiB | 6.40 MiB/s, done.
     Resolving deltas: 100% (272761/272761), done.
     Checking connectivity... done.
                    </literallayout>
                    Once the repository is created, you can change to that
                    directory and check its status and list its branches:
                    <literallayout class='monospaced'>
     $ cd ~/poky
     $ git status
     On branch master
     Your branch is up-to-date with 'origin/master'.
     nothing to commit, working directory clean
     $ git branch
     * master
                    </literallayout>
                    Your local repository of poky is identical to the
                    upstream poky repository at the time from which it was
                    cloned.
                    By default, Git creates the "master" branch and checks
                    it out.
                    </para></listitem>
            </orderedlist>
        </para>
    </section>

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

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

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

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

        <para>
            Similar to branches, the upstream repository has tags used
            to mark significant commits such as a completed release or
            stage of a release.
            You might want to set up a local branch based on one of those
            points in the repository.
            The process is similar to checking out by branch name except you
            use tag names.
            <orderedlist>
                <listitem><para>
                    <emphasis>Switch to the Poky Directory:</emphasis>
                    If you have a local poky Git repository, switch to that
                    directory.
                    If you do not have the local copy of poky, see the
                    "<link linkend='cloning-the-poky-repository'>Cloning the <filename>poky</filename> Repository</link>"
                    section.
                    </para></listitem>
                <listitem><para>
                    <emphasis>Fetch the Tag Names:</emphasis>
                    To checkout the branch based on a tag name, you need to
                    fetch the upstream tags into your local repository:
                    <literallayout class='monospaced'>
     $ git fetch --tags
     $
                    </literallayout>
                    </para></listitem>
                <listitem><para>
                    <emphasis>List the Tag Names:</emphasis>
                    You can list the tag names now:
                    <literallayout class='monospaced'>
     $ git tag
     1.1_M1.final
     1.1_M1.rc1
     1.1_M1.rc2
     1.1_M2.final
     1.1_M2.rc1
        .
        .
        .
     yocto-2.2
     yocto-2.2.1
     yocto-2.3
     yocto_1.5_M5.rc8
                    </literallayout>
                    </para></listitem>
                <listitem><para>
                    <emphasis>Checkout the Branch:</emphasis>
                    <literallayout class='monospaced'>
     $ git checkout tags/2.2_M2 -b my_yocto_2.2_M2
     Switched to a new branch 'my_yocto_2.2_M2'
     $ git branch
       master
     * my_yocto_2.2_M2
                    </literallayout>
                    The previous command creates and checks out a local
                    branch named "my_yocto_2.2_M2", which is based on
                    the commit in the upstream poky repository that has
                    the same tag.
                    The files you have available locally when you are
                    checked out to that branch are a snapshot of the
                    "morty" development branch at the point where
                    milestone two was reached.
                    </para></listitem>
            </orderedlist>
        </para>
    </section>
</section>

<section id='building-images'>
    <title>Building Images</title>

    <para>
        The build process creates an entire Linux distribution, including the toolchain, from source.
        For more information on this topic, see the
        "<ulink url='&YOCTO_DOCS_QS_URL;#qs-building-images'>Building Images</ulink>"
        section in the Yocto Project Quick Start.
    </para>

    <para>
        The build process is as follows:
        <orderedlist>
            <listitem><para>Make sure you have set up the Source Directory described in the
                previous section.</para></listitem>
            <listitem><para>Initialize the build environment by sourcing a build
                environment script (i.e.
                <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>
                or
                <ulink url='&YOCTO_DOCS_REF_URL;#structure-memres-core-script'><filename>oe-init-build-env-memres</filename></ulink>).
                </para></listitem>
            <listitem><para>Optionally ensure the <filename>conf/local.conf</filename> configuration file,
                which is found in the
                <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>,
                is set up how you want it.
                This file defines many aspects of the build environment including
                the target machine architecture through the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'>MACHINE</ulink></filename> variable,
                the packaging format used during the build
                (<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_CLASSES'><filename>PACKAGE_CLASSES</filename></ulink>),
                and a centralized tarball download directory through the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-DL_DIR'>DL_DIR</ulink></filename> variable.</para></listitem>
            <listitem><para>
                Build the image using the <filename>bitbake</filename> command.
                If you want information on BitBake, see the
                <ulink url='&YOCTO_DOCS_BB_URL;'>BitBake User Manual</ulink>.
                </para></listitem>
            <listitem><para>Run the image either on the actual hardware or using the QEMU
                emulator.</para></listitem>
        </orderedlist>
    </para>
</section>

<section id='flashing-images-using-bmaptool'>
    <title>Flashing Images Using <filename>bmaptool</filename></title>

    <para>
        An easy way to flash an image to a bootable device is to use
        <filename>bmaptool</filename>, which is integrated into the
        OpenEmbedded build system.
    </para>

    <para>
        Following, is an example that shows how to flash a Wic image.
        <note>
            You can use <filename>bmaptool</filename> to flash any
            type of image.
        </note>
        Use these steps to flash an image using
        <filename>bmaptool</filename>:
        <note>
            Unless you are able to install the
            <filename>bmap-tools</filename> package as mentioned in the note
            in the second bullet of step 3 further down, you will need to build
            <filename>bmaptool</filename> before using it.
            Build the tool using the following command:
            <literallayout class='monospaced'>
     $ bitbake bmap-tools-native
            </literallayout>
        </note>
        <orderedlist>
            <listitem><para>
                Add the following to your <filename>local.conf</filename>
                file:
                <literallayout class='monospaced'>
     IMAGE_FSTYPES += "wic wic.bmap"
                </literallayout>
                </para></listitem>
            <listitem><para>
                Either have your image ready (pre-built) or take the step
                build the image:
                <literallayout class='monospaced'>
     $ bitbake <replaceable>image</replaceable>
                </literallayout>
                </para></listitem>
            <listitem><para>
                Flash the image to the media by using
                <filename>bmaptool</filename> depending on your particular
                setup:
                <itemizedlist>
                    <listitem><para>
                        If you have write access to the media,
                        use this command form:
                        <literallayout class='monospaced'>
     $ oe-run-native bmaptool-native bmaptool copy ./tmp/deploy/images/qemux86-64-core-image-minimal-<replaceable>machine</replaceable>.wic /dev/sd<replaceable>X</replaceable>
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        If you do not have write access to
                        the media, use the following
                        commands:
                        <literallayout class='monospaced'>
     $ sudo bash
     $ PATH=tmp/sysroots/x86_64-linux/usr/bin/ bmaptool copy ./tmp/deploy/images/qemux86-64/core-image-minimal-<replaceable>machine</replaceable>.wic /dev/sd<replaceable>X</replaceable>
                        </literallayout>
                        <note>
                            If you are using Ubuntu or Debian distributions,
                            you can install the
                            <filename>bmap-tools</filename> package using the
                            following command and then use the tool
                            without specifying
                            <filename>PATH</filename> even from the
                            root account:
                            <literallayout class='monospaced'>
     $ sudo apt-get install bmap-tools
                            </literallayout>
                        </note>
                        </para></listitem>
                </itemizedlist>
                </para></listitem>
        </orderedlist>
    </para>

    <para>
        For help on the <filename>bmaptool</filename> command, use the
        following command:
        <literallayout class='monospaced'>
     $ bmaptool --help
        </literallayout>
    </para>
</section>

<section id='using-pre-built-binaries-and-qemu'>
    <title>Using Pre-Built Binaries and QEMU</title>

    <para>
        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 "<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>"
        chapter in the Yocto Project Reference Manual
        for descriptions of the types of binaries that ship with a Yocto Project
        release.
    </para>

    <para>
        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 (i.e. a toolchain designed to
        run on the
        <ulink url='&YOCTO_DOCS_REF_URL;#var-SDKMACHINE'><filename>SDKMACHINE</filename></ulink>).
        If you are not using an SDK type image, you need to separately download
        and install the stand-alone Yocto Project cross-toolchain tarball.
        See the
        "<ulink url='&YOCTO_DOCS_SDK_URL;#sdk-appendix-obtain'>Obtaining the SDK</ulink>"
        appendix in the Yocto Project Software Development Kit (SDK)
        Developer's Guide for more information on locating and installing
        cross-toolchains.
    </para>

    <para>
        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 file systems from
        <ulink url='&YOCTO_MACHINES_DL_URL;'>machines</ulink>.
        You can get installation scripts for stand-alone toolchains from
        <ulink url='&YOCTO_TOOLCHAIN_DL_URL;'>toolchains</ulink>.
        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
        <ulink url='&YOCTO_DOCS_SDK_URL;#sdk-manual'>Yocto Project Software Development Kit (SDK) Developer's Guide</ulink>.
        You can learn more about using QEMU with the Yocto Project in the
        "<link linkend='dev-manual-qemu'>Using the Quick EMUlator (QEMU)</link>"
        section.
    </para>

    <para>
        Using QEMU to emulate your hardware can result in speed issues
        depending on the target and host architecture mix.
        For example, using the <filename>qemux86</filename> 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 <filename>qemuarm</filename> image on the same Intel-based
        host can be slower.
        But, you still achieve faithful emulation of ARM-specific issues.
    </para>

    <para>
        To speed things up, the QEMU images support using <filename>distcc</filename>
        to call a cross-compiler outside the emulated system.
        If you used <filename>runqemu</filename> to start QEMU, and the
        <filename>distccd</filename> 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 <filename>distcc</filename>.
        You can accomplish this by defining the cross-compiler variable
        (e.g. <filename>export CC="distcc"</filename>).
        Alternatively, if you are using a suitable SDK image or the appropriate
        stand-alone toolchain is present,
        the toolchain is also automatically used.
    </para>

    <note>
        Several mechanisms exist that let you connect to the system running on the
        QEMU emulator:
        <itemizedlist>
            <listitem><para>QEMU provides a framebuffer interface that makes standard
                consoles available.</para></listitem>
            <listitem><para>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.</para></listitem>
            <listitem><para>
                SSH servers exist in some QEMU images.
                The <filename>core-image-sato</filename> QEMU image has a
                Dropbear secure shell (SSH) server that runs with the root
                password disabled.
                The <filename>core-image-full-cmdline</filename> and
                <filename>core-image-lsb</filename> QEMU images
                have OpenSSH instead of Dropbear.
                Including these SSH servers allow you to use standard
                <filename>ssh</filename> and <filename>scp</filename> commands.
                The <filename>core-image-minimal</filename> QEMU image,
                however, contains no SSH server.
                </para></listitem>
            <listitem><para>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
                <filename>runqemu-extract-sdk</filename> command.
                After running the command, you must then point the <filename>runqemu</filename>
                script to the extracted directory instead of a root filesystem image file.</para></listitem>
        </itemizedlist>
    </note>
</section>
</chapter>
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