summaryrefslogtreecommitdiffstats
path: root/documentation/dev-manual/dev-manual-common-tasks.xml
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<!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='extendpoky'>

<title>Common Tasks</title>
    <para>
        This chapter describes fundamental procedures such as creating layers,
        adding new software packages, extending or customizing images,
        porting work to new hardware (adding a new machine), and so forth.
        You will find that the procedures documented here occur often in the
        development cycle using the Yocto Project.
    </para>

    <section id="understanding-and-creating-layers">
        <title>Understanding and Creating Layers</title>

        <para>
            The OpenEmbedded build system supports organizing
            <link linkend='metadata'>Metadata</link> 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 your Metadata, the easier
            it is to cope with future changes.
        </para>

        <para>
            To illustrate how layers are used to keep things modular, consider
            machine customizations.
            These types of customizations typically reside in a special layer,
            rather than a general layer, called a Board Support Package (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 of 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
            (<filename>.bbappend</filename>) file, which is described later
            in this section.
        </para>

        <para>
        </para>

        <section id='yocto-project-layers'>
            <title>Layers</title>

            <para>
                The <link linkend='source-directory'>Source Directory</link>
                contains both general layers and BSP
                layers right out of the box.
                You can easily identify layers that ship with a
                Yocto Project release in the Source Directory by their
                folder names.
                Folders that represent layers typically have names that begin with
                the string <filename>meta-</filename>.
                <note>
                    It is not a requirement that a layer name begin with the
                    prefix <filename>meta-</filename>, but it is a commonly
                    accepted standard in the Yocto Project community.
                </note>
                For example, when you set up the Source Directory structure,
                you will see several layers:
                <filename>meta</filename>,
                <filename>meta-skeleton</filename>,
                <filename>meta-selftest</filename>,
                <filename>meta-poky</filename>, and
                <filename>meta-yocto-bsp</filename>.
                Each of these folders represents a distinct layer.
            </para>

            <para>
                As another example, if you set up a local copy of the
                <filename>meta-intel</filename> Git repository
                and then explore the folder of that general layer,
                you will discover many Intel-specific BSP layers inside.
                For more information on BSP layers, 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.
            </para>
        </section>

        <section id='creating-your-own-layer'>
            <title>Creating Your Own Layer</title>

            <para>
                It is very easy to create your own layers to use with the
                OpenEmbedded build system.
                The Yocto Project ships with scripts that speed up creating
                general layers and BSP layers.
                This section describes the steps you perform by hand to create
                a layer so that you can better understand them.
                For information about the layer-creation scripts, see the
                "<ulink url='&YOCTO_DOCS_BSP_URL;#creating-a-new-bsp-layer-using-the-yocto-bsp-script'>Creating a New BSP Layer Using the yocto-bsp Script</ulink>"
                section in the Yocto Project Board Support Package (BSP)
                Developer's Guide and the
                "<link linkend='creating-a-general-layer-using-the-yocto-layer-script'>Creating a General Layer Using the yocto-layer Script</link>"
                section further down in this manual.
            </para>

            <para>
                Follow these general steps to create your layer:
                <orderedlist>
                    <listitem><para><emphasis>Check Existing Layers:</emphasis>
                        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
                        <ulink url='http://layers.openembedded.org/layerindex/layers/'><filename>OpenEmbedded Metadata Index</filename></ulink>
                        for a list of layers from the OpenEmbedded community
                        that can be used in the Yocto Project.
                        </para></listitem>
                    <listitem><para><emphasis>Create a Directory:</emphasis>
                        Create the directory for your layer.
                        While not strictly required, prepend the name of the
                        folder with the string <filename>meta-</filename>.
                        For example:
                        <literallayout class='monospaced'>
     meta-mylayer
     meta-GUI_xyz
     meta-mymachine
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Create a Layer Configuration
                       File:</emphasis>
                       Inside your new layer folder, you need to create a
                       <filename>conf/layer.conf</filename> file.
                       It is easiest to take an existing layer configuration
                       file and copy that to your layer's
                       <filename>conf</filename> directory and then modify the
                       file as needed.</para>
                       <para>The
                       <filename>meta-yocto-bsp/conf/layer.conf</filename> file
                       demonstrates the required syntax:
                       <literallayout class='monospaced'>
     # We have a conf and classes directory, add to BBPATH
     BBPATH .= ":${LAYERDIR}"

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

     BBFILE_COLLECTIONS += "yoctobsp"
     BBFILE_PATTERN_yoctobsp = "^${LAYERDIR}/"
     BBFILE_PRIORITY_yoctobsp = "5"
     LAYERVERSION_yoctobsp = "3"
                        </literallayout></para>
                        <para>Here is an explanation of the example:
                        <itemizedlist>
                            <listitem><para>The configuration and
                                classes directory is appended to
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-BBPATH'><filename>BBPATH</filename></ulink>.
                                <note>
                                    All non-distro layers, which include all BSP
                                    layers, are expected to append the layer
                                    directory to the
                                    <filename>BBPATH</filename>.
                                    On the other hand, distro layers, such as
                                    <filename>meta-poky</filename>, can choose
                                    to enforce their own precedence over
                                    <filename>BBPATH</filename>.
                                    For an example of that syntax, see the
                                    <filename>layer.conf</filename> file for
                                    the <filename>meta-poky</filename> layer.
                                </note></para></listitem>
                            <listitem><para>The recipes for the layers are
                                appended to
                                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILES'>BBFILES</ulink></filename>.
                                </para></listitem>
                            <listitem><para>The
                                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_COLLECTIONS'>BBFILE_COLLECTIONS</ulink></filename>
                                variable is then appended with the layer name.
                                </para></listitem>
                            <listitem><para>The
                                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PATTERN'>BBFILE_PATTERN</ulink></filename>
                                variable is set to a regular expression and is
                                used to match files from
                                <filename>BBFILES</filename> into a particular
                                layer.
                                In this case,
                                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LAYERDIR'>LAYERDIR</ulink></filename>
                                is used to make <filename>BBFILE_PATTERN</filename> match within the
                                layer's path.</para></listitem>
                            <listitem><para>The
                                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PRIORITY'>BBFILE_PRIORITY</ulink></filename>
                                variable then assigns a priority to the layer.
                                Applying priorities is useful in situations
                                where the same recipe might appear in multiple
                                layers and allows you to choose the layer
                                that takes precedence.</para></listitem>
                            <listitem><para>The
                                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LAYERVERSION'>LAYERVERSION</ulink></filename>
                                variable optionally specifies the version of a
                                layer as a single number.</para></listitem>
                        </itemizedlist></para>
                        <para>Note the use of the
                        <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LAYERDIR'>LAYERDIR</ulink></filename>
                        variable, which expands to the directory of the current
                        layer.</para>
                        <para>Through the use of the <filename>BBPATH</filename>
                        variable, BitBake locates class files
                        (<filename>.bbclass</filename>),
                        configuration files, and files that are included
                        with <filename>include</filename> and
                        <filename>require</filename> statements.
                        For these cases, BitBake uses the first file that
                        matches the name found in <filename>BBPATH</filename>.
                        This is similar to the way the <filename>PATH</filename>
                        variable is used for binaries.
                        It is recommended, therefore, that you use unique
                        class and configuration
                        filenames in your custom layer.</para></listitem>
                    <listitem><para><emphasis>Add Content:</emphasis> Depending
                        on the type of layer, add the content.
                        If the layer adds support for a machine, add the machine
                        configuration in a <filename>conf/machine/</filename>
                        file within the layer.
                        If the layer adds distro policy, add the distro
                        configuration in a <filename>conf/distro/</filename>
                        file within the layer.
                        If the layer introduces new recipes, put the recipes
                        you need in <filename>recipes-*</filename>
                        subdirectories within the layer.
                        <note>In order to be compliant with the Yocto Project,
                            a layer must contain a
                            <ulink url='&YOCTO_DOCS_BSP_URL;#bsp-filelayout-readme'>README file.</ulink>
                            </note></para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='best-practices-to-follow-when-creating-layers'>
            <title>Best Practices to Follow When Creating Layers</title>

            <para>
                To create layers that are easier to maintain and that will
                not impact builds for other machines, you should consider the
                information in the following sections.
            </para>

            <section id='avoid-overlaying-entire-recipes'>
                <title>Avoid "Overlaying" Entire Recipes</title>

                <para>
                    Avoid "overlaying" entire recipes from other layers in your
                    configuration.
                    In other words, do not copy an entire recipe into your
                    layer and then modify it.
                    Rather, use an append file (<filename>.bbappend</filename>)
                    to override
                    only those parts of the original recipe you need to modify.
                </para>
            </section>

            <section id='avoid-duplicating-include-files'>
                <title>Avoid Duplicating Include Files</title>

                <para>
                    Avoid duplicating include files.
                    Use append files (<filename>.bbappend</filename>)
                    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
                    <filename>require recipes-core/</filename><replaceable>package</replaceable><filename>/</filename><replaceable>file</replaceable><filename>.inc</filename>
                    instead of <filename>require </filename><replaceable>file</replaceable><filename>.inc</filename>.
                    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 should try to address that
                    deficiency instead of overlaying the include file.
                    For example, you could address this by getting the
                    maintainer of the include file to add a variable or
                    variables to make it easy to override the parts needing
                    to be overridden.
                </para>
            </section>

            <section id='structure-your-layers'>
                <title>Structure Your Layers</title>

                <para>
                    Proper use of overrides within append files and placement
                    of machine-specific files within your layer can ensure that
                    a build is not using the wrong Metadata and negatively
                    impacting a build for a different machine.
                    Following are some examples:
                    <itemizedlist>
                        <listitem><para><emphasis>Modifying Variables to Support
                            a Different Machine:</emphasis>
                            Suppose you have a layer named
                            <filename>meta-one</filename> that adds support
                            for building machine "one".
                            To do so, you use an append file named
                            <filename>base-files.bbappend</filename> and
                            create a dependency on "foo" by altering the
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
                            variable:
                            <literallayout class='monospaced'>
     DEPENDS = "foo"
                            </literallayout>
                            The dependency is created during any build that
                            includes the layer
                            <filename>meta-one</filename>.
                            However, you might not want this dependency
                            for all machines.
                            For example, suppose you are building for
                            machine "two" but your
                            <filename>bblayers.conf</filename> file has the
                            <filename>meta-one</filename> layer included.
                            During the build, the
                            <filename>base-files</filename> for machine
                            "two" will also have the dependency on
                            <filename>foo</filename>.</para>
                            <para>To make sure your changes apply only when
                            building machine "one", use a machine override
                            with the <filename>DEPENDS</filename> statement:
                            <literallayout class='monospaced'>
     DEPENDS_one = "foo"
                            </literallayout>
                            You should follow the same strategy when using
                            <filename>_append</filename> and
                            <filename>_prepend</filename> operations:
                            <literallayout class='monospaced'>
     DEPENDS_append_one = " foo"
     DEPENDS_prepend_one = "foo "
                            </literallayout>
                            As an actual example, here's a line from the recipe
                            for gnutls, which adds dependencies on
                            "argp-standalone" when building with the musl C
                            library:
                            <literallayout class='monospaced'>
     DEPENDS_append_libc-musl = " argp-standalone"
                            </literallayout>
                            <note>
                                Avoiding "+=" and "=+" and using
                                machine-specific
                                <filename>_append</filename>
                                and <filename>_prepend</filename> operations
                                is recommended as well.
                            </note></para></listitem>
                        <listitem><para><emphasis>Place Machine-Specific Files
                            in Machine-Specific Locations:</emphasis>
                            When you have a base recipe, such as
                            <filename>base-files.bb</filename>, that
                            contains a
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                            statement to a file, you can use an append file
                            to cause the build to use your own version of
                            the file.
                            For example, an append file in your layer at
                            <filename>meta-one/recipes-core/base-files/base-files.bbappend</filename>
                            could extend
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink>
                            using
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
                            as follows:
                            <literallayout class='monospaced'>
     FILESEXTRAPATHS_prepend := "${THISDIR}/${BPN}:"
                            </literallayout>
                            The build for machine "one" will pick up your
                            machine-specific file as long as you have the
                            file in
                            <filename>meta-one/recipes-core/base-files/base-files/</filename>.
                            However, if you are building for a different
                            machine and the
                            <filename>bblayers.conf</filename> file includes
                            the <filename>meta-one</filename> layer and
                            the location of your machine-specific file is
                            the first location where that file is found
                            according to <filename>FILESPATH</filename>,
                            builds for all machines will also use that
                            machine-specific file.</para>
                            <para>You can make sure that a machine-specific
                            file is used for a particular machine by putting
                            the file in a subdirectory specific to the
                            machine.
                            For example, rather than placing the file in
                            <filename>meta-one/recipes-core/base-files/base-files/</filename>
                            as shown above, put it in
                            <filename>meta-one/recipes-core/base-files/base-files/one/</filename>.
                            Not only does this make sure the file is used
                            only when building for machine "one", but the
                            build process locates the file more quickly.</para>
                            <para>In summary, you need to place all files
                            referenced from <filename>SRC_URI</filename>
                            in a machine-specific subdirectory within the
                            layer in order to restrict those files to
                            machine-specific builds.</para></listitem>
                    </itemizedlist>
                </para>
            </section>

            <section id='other-recommendations'>
                <title>Other Recommendations</title>

                <para>
                    We also recommend the following:
                    <itemizedlist>
                        <listitem><para>Store custom layers in a Git repository
                            that uses the
                            <filename>meta-<replaceable>layer_name</replaceable></filename> format.
                            </para></listitem>
                        <listitem><para>Clone the repository alongside other
                            <filename>meta</filename> directories in the
                            <link linkend='source-directory'>Source Directory</link>.
                            </para></listitem>
                     </itemizedlist>
                     Following these recommendations keeps your Source Directory and
                     its configuration entirely inside the Yocto Project's core
                     base.
                </para>
            </section>
        </section>

        <section id='enabling-your-layer'>
            <title>Enabling Your Layer</title>

            <para>
                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
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBLAYERS'>BBLAYERS</ulink></filename>
                variable in your <filename>conf/bblayers.conf</filename> file,
                which is found in the
                <link linkend='build-directory'>Build Directory</link>.
                The following example shows how to enable a layer named
                <filename>meta-mylayer</filename>:
                <literallayout class='monospaced'>
     LCONF_VERSION = "6"

     BBPATH = "${TOPDIR}"
     BBFILES ?= ""

     BBLAYERS ?= " \
       $HOME/poky/meta \
       $HOME/poky/meta-poky \
       $HOME/poky/meta-yocto-bsp \
       $HOME/poky/meta-mylayer \
       "
                </literallayout>
            </para>

            <para>
                BitBake parses each <filename>conf/layer.conf</filename> file
                as specified in the <filename>BBLAYERS</filename> variable
                within the <filename>conf/bblayers.conf</filename> file.
                During the processing of each
                <filename>conf/layer.conf</filename> file, BitBake adds the
                recipes, classes and configurations contained within the
                particular layer to the source directory.
            </para>
        </section>

        <section id='using-bbappend-files'>
            <title>Using .bbappend Files</title>

            <para>
                Recipes used to append Metadata to other recipes are called
                BitBake append files.
                BitBake append files use the <filename>.bbappend</filename> file
                type suffix, while the corresponding recipes to which Metadata
                is being appended use the <filename>.bb</filename> file type
                suffix.
            </para>

            <para>
                A <filename>.bbappend</filename> 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 <filename>.bbappend</filename> file resides in your layer,
                while the main <filename>.bb</filename> recipe file to
                which you are appending Metadata resides in a different layer.
            </para>

            <para>
                Append files must have the same root names as their corresponding
                recipes.
                For example, the append file
                <filename>someapp_&DISTRO;.bbappend</filename> must apply to
                <filename>someapp_&DISTRO;.bb</filename>.
                This means the original recipe and append file names are version
                number-specific.
                If the corresponding recipe is renamed to update to a newer
                version, the corresponding <filename>.bbappend</filename> file must
                be renamed (and possibly updated) as well.
                During the build process, BitBake displays an error on starting
                if it detects a <filename>.bbappend</filename> file that does
                not have a corresponding recipe with a matching name.
                See the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BB_DANGLINGAPPENDS_WARNONLY'><filename>BB_DANGLINGAPPENDS_WARNONLY</filename></ulink>
                variable for information on how to handle this error.
            </para>

            <para>
                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.
            </para>

            <para>
                As an example, consider the main formfactor recipe and a
                corresponding formfactor append file both from the
                <link linkend='source-directory'>Source Directory</link>.
                Here is the main formfactor recipe, which is named
                <filename>formfactor_0.0.bb</filename> and located in the
                "meta" layer at
                <filename>meta/recipes-bsp/formfactor</filename>:
                <literallayout class='monospaced'>
     SUMMARY = "Device formfactor information"
     SECTION = "base"
     LICENSE = "MIT"
     LIC_FILES_CHKSUM = "file://${COREBASE}/LICENSE;md5=4d92cd373abda3937c2bc47fbc49d690 \
                    file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420"
     PR = "r45"

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

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

     do_install() {
	     # Install file only if it has 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
     }
                </literallayout>
                In the main recipe, note the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                variable, which tells the OpenEmbedded build system where to
                find files during the build.
            </para>

            <para>
                Following is the append file, which is named
                <filename>formfactor_0.0.bbappend</filename> and is from the
                Raspberry Pi BSP Layer named
                <filename>meta-raspberrypi</filename>.
                The file is in <filename>recipes-bsp/formfactor</filename>:
                <literallayout class='monospaced'>
     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
                </literallayout>
            </para>

            <para>
                By default, the build system uses the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink>
                variable to locate files.
                This append file extends the locations by setting the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
                variable.
                Setting this variable in the <filename>.bbappend</filename>
                file is the most reliable and recommended method for adding
                directories to the search path used by the build system
                to find files.
            </para>

            <para>
                The statement in this example extends the directories to include
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-THISDIR'><filename>THISDIR</filename></ulink><filename>}/${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink><filename>}</filename>,
                which resolves to a directory named
                <filename>formfactor</filename> in the same directory
                in which the append file resides (i.e.
                <filename>meta-raspberrypi/recipes-bsp/formfactor/formfactor</filename>.
                This implies that you must have the supporting directory
                structure set up that will contain any files or patches you
                will be including from the layer.
            </para>

            <para>
                Using the immediate expansion assignment operator
                <filename>:=</filename> is important because of the reference to
                <filename>THISDIR</filename>.
                The trailing colon character is important as it ensures that
                items in the list remain colon-separated.
                <note>
                    <para>
                        BitBake automatically defines the
                        <filename>THISDIR</filename> variable.
                        You should never set this variable yourself.
                        Using "_prepend" as part of the
                        <filename>FILESEXTRAPATHS</filename> ensures your path
                        will be searched prior to other paths in the final
                        list.
                    </para>

                    <para>
                        Also, not all append files add extra files.
                        Many append files simply exist to add build options
                        (e.g. <filename>systemd</filename>).
                        For these cases, your append file would not even
                        use the <filename>FILESEXTRAPATHS</filename> statement.
                    </para>
                </note>
            </para>
        </section>

        <section id='prioritizing-your-layer'>
            <title>Prioritizing Your Layer</title>

            <para>
                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 takes precedence.
                Priority values also affect the order in which multiple
                <filename>.bbappend</filename> 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.
            </para>

            <para>
                To specify the layer's priority manually, use the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PRIORITY'><filename>BBFILE_PRIORITY</filename></ulink>
                variable.
                For example:
                <literallayout class='monospaced'>
     BBFILE_PRIORITY_mylayer = "1"
                </literallayout>
            </para>

            <note>
                <para>It is possible for a recipe with a lower version number
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
                in a layer that has a higher priority to take precedence.</para>
                <para>Also, the layer priority does not currently affect the
                precedence order of <filename>.conf</filename>
                or <filename>.bbclass</filename> files.
                Future versions of BitBake might address this.</para>
            </note>
        </section>

        <section id='managing-layers'>
            <title>Managing Layers</title>

            <para>
                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
                <filename>.bbappend</filename> files and their applicable
                recipes can help to reveal potential problems.
            </para>

            <para>
                Use the following form when running the layer management tool.
                <literallayout class='monospaced'>
     $ bitbake-layers <replaceable>command</replaceable> [<replaceable>arguments</replaceable>]
                </literallayout>
                The following list describes the available commands:
                <itemizedlist>
                    <listitem><para><filename><emphasis>help:</emphasis></filename>
                        Displays general help or help on a specified command.
                        </para></listitem>
                    <listitem><para><filename><emphasis>show-layers:</emphasis></filename>
                        Shows the current configured layers.
                        </para></listitem>
                    <listitem><para><filename><emphasis>show-recipes:</emphasis></filename>
                        Lists available recipes and the layers that provide them.
                        </para></listitem>
                    <listitem><para><filename><emphasis>show-overlayed:</emphasis></filename>
                        Lists overlayed recipes.
                        A recipe is overlayed when a recipe with the same name
                        exists in another layer that has a higher layer
                        priority.
                        </para></listitem>
                    <listitem><para><filename><emphasis>show-appends:</emphasis></filename>
                        Lists <filename>.bbappend</filename> files and the
                        recipe files to which they apply.
                        </para></listitem>
                    <listitem><para><filename><emphasis>show-cross-depends:</emphasis></filename>
                        Lists dependency relationships between recipes that
                        cross layer boundaries.
                        </para></listitem>
                    <listitem><para><filename><emphasis>add-layer:</emphasis></filename>
                        Adds a layer to <filename>bblayers.conf</filename>.
                        </para></listitem>
                    <listitem><para><filename><emphasis>remove-layer:</emphasis></filename>
                        Removes a layer from <filename>bblayers.conf</filename>
                        </para></listitem>
                    <listitem><para><filename><emphasis>flatten:</emphasis></filename>
                        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
                        <filename>.bbappend</filename> files appended to the
                        corresponding recipes.
                        You might have to perform some manual cleanup of the
                        flattened layer as follows:
                        <itemizedlist>
                            <listitem><para>Non-recipe files (such as patches)
                                are overwritten.
                                The flatten command shows a warning for these
                                files.
                                </para></listitem>
                            <listitem><para>Anything beyond the normal layer
                                setup has been added to the
                                <filename>layer.conf</filename> file.
                                Only the lowest priority layer's
                                <filename>layer.conf</filename> is used.
                                </para></listitem>
                            <listitem><para>Overridden and appended items from
                                <filename>.bbappend</filename> files need to be
                                cleaned up.
                                The contents of each
                                <filename>.bbappend</filename> 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 <filename>bitbake-layers</filename>
                                command adds the line
                                <filename>#### bbappended ...</filename> so that
                                you know where the following lines originate:
                                <literallayout class='monospaced'>
     ...
     DESCRIPTION = "A useful utility"
     ...
     EXTRA_OECONF = "--enable-something"
     ...

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

     DESCRIPTION = "Customized utility"
     EXTRA_OECONF += "--enable-somethingelse"
                                </literallayout>
                                Ideally, you would tidy up these utilities as
                                follows:
                                <literallayout class='monospaced'>
     ...
     DESCRIPTION = "Customized utility"
     ...
     EXTRA_OECONF = "--enable-something --enable-somethingelse"
     ...
                                </literallayout></para></listitem>
                        </itemizedlist></para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='creating-a-general-layer-using-the-yocto-layer-script'>
            <title>Creating a General Layer Using the yocto-layer Script</title>

            <para>
                The <filename>yocto-layer</filename> script simplifies
                creating a new general layer.
                <note>
                    For information on BSP layers, see the
                    "<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>"
                    section in the Yocto Project Board Specific (BSP)
                    Developer's Guide.
                </note>
                The default mode of the script's operation is to prompt you for
                information needed to generate the layer:
                <itemizedlist>
                    <listitem><para>The layer priority.
                        </para></listitem>
                    <listitem><para>Whether or not to create a sample recipe.
                        </para></listitem>
                    <listitem><para>Whether or not to create a sample
                        append file.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                Use the <filename>yocto-layer create</filename> sub-command
                to create a new general layer.
                In its simplest form, you can create a layer as follows:
                <literallayout class='monospaced'>
     $ yocto-layer create mylayer
                </literallayout>
                The previous example creates a layer named
                <filename>meta-mylayer</filename> in the current directory.
            </para>

            <para>
                As the <filename>yocto-layer create</filename> command runs,
                default values for the prompts appear in brackets.
                Pressing enter without supplying anything for the prompts
                or pressing enter and providing an invalid response causes the
                script to accept the default value.
                Once the script completes, the new layer
                is created in the current working directory.
                The script names the layer by prepending
                <filename>meta-</filename> to the name you provide.
            </para>

            <para>
                Minimally, the script creates the following within the layer:
                <itemizedlist>
                    <listitem><para><emphasis>The <filename>conf</filename>
                        directory:</emphasis>
                        This directory contains the layer's configuration file.
                        The root name for the file is the same as the root name
                        your provided for the layer (e.g.
                        <filename><replaceable>layer</replaceable>.conf</filename>).
                        </para></listitem>
                    <listitem><para><emphasis>The
                        <filename>COPYING.MIT</filename> file:</emphasis>
                        The copyright and use notice for the software.
                        </para></listitem>
                    <listitem><para><emphasis>The <filename>README</filename>
                        file:</emphasis>
                        A file describing the contents of your new layer.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                If you choose to generate a sample recipe file, the script
                prompts you for the name for the recipe and then creates it
                in <filename><replaceable>layer</replaceable>/recipes-example/example/</filename>.
                The script creates a <filename>.bb</filename> file and a
                directory, which contains a sample
                <filename>helloworld.c</filename> source file, along with
                a sample patch file.
                If you do not provide a recipe name, the script uses
                "example".
            </para>

            <para>
                If you choose to generate a sample append file, the script
                prompts you for the name for the file and then creates it
                in <filename><replaceable>layer</replaceable>/recipes-example-bbappend/example-bbappend/</filename>.
                The script creates a <filename>.bbappend</filename> file and a
                directory, which contains a sample patch file.
                If you do not provide a recipe name, the script uses
                "example".
                The script also prompts you for the version of the append file.
                The version should match the recipe to which the append file
                is associated.
            </para>

            <para>
                The easiest way to see how the <filename>yocto-layer</filename>
                script works is to experiment with the script.
                You can also read the usage information by entering the
                following:
                <literallayout class='monospaced'>
     $ yocto-layer help
                </literallayout>
            </para>

            <para>
                Once you create your general layer, you must add it to your
                <filename>bblayers.conf</filename> file.
                Here is an example where a layer named
                <filename>meta-mylayer</filename> is added:
                <literallayout class='monospaced'>
     BBLAYERS = ?" \
        /usr/local/src/yocto/meta \
        /usr/local/src/yocto/meta-poky \
        /usr/local/src/yocto/meta-yocto-bsp \
        /usr/local/src/yocto/meta-mylayer \
        "
                </literallayout>
                Adding the layer to this file enables the build system to
                locate the layer during the build.
                </para>
        </section>
    </section>

    <section id='usingpoky-extend-customimage'>
        <title>Customizing Images</title>

        <para>
            You can customize images to satisfy particular requirements.
            This section describes several methods and provides guidelines for each.
        </para>

        <section id='usingpoky-extend-customimage-localconf'>
            <title>Customizing Images Using <filename>local.conf</filename></title>

            <para>
                Probably the easiest way to customize an image is to add a
                package by way of the <filename>local.conf</filename>
                configuration 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 are in effect for every
                build and consequently affect all images, which might not
                be what you require.
            </para>

            <para>
                To add a package to your image using the local configuration
                file, use the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'>IMAGE_INSTALL</ulink></filename>
                variable with the <filename>_append</filename> operator:
                <literallayout class='monospaced'>
     IMAGE_INSTALL_append = " strace"
                </literallayout>
                Use of the syntax is important - specifically, the space between
                the quote and the package name, which is
                <filename>strace</filename> in this example.
                This space is required since the <filename>_append</filename>
                operator does not add the space.
            </para>

            <para>
                Furthermore, you must use <filename>_append</filename> instead
                of the <filename>+=</filename> 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
                <filename>.bbclass</filename> files with operators like
                <filename>?=</filename>.
                Using <filename>_append</filename> ensures the operation takes
                affect.
            </para>

            <para>
                As shown in its simplest use,
                <filename>IMAGE_INSTALL_append</filename> affects all images.
                It is possible to extend the syntax so that the variable
                applies to a specific image only.
                Here is an example:
                <literallayout class='monospaced'>
     IMAGE_INSTALL_append_pn-core-image-minimal = " strace"
                </literallayout>
                This example adds <filename>strace</filename> to the
                <filename>core-image-minimal</filename> image only.
            </para>

            <para>
                You can add packages using a similar approach through the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-CORE_IMAGE_EXTRA_INSTALL'>CORE_IMAGE_EXTRA_INSTALL</ulink></filename>
                variable.
                If you use this variable, only
                <filename>core-image-*</filename> images are affected.
            </para>
        </section>

        <section id='usingpoky-extend-customimage-imagefeatures'>
            <title>Customizing Images Using Custom <filename>IMAGE_FEATURES</filename> and
                <filename>EXTRA_IMAGE_FEATURES</filename></title>

            <para>
                Another method for customizing your image is to enable or
                disable high-level image features by using the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
                and <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_IMAGE_FEATURES'><filename>EXTRA_IMAGE_FEATURES</filename></ulink>
                variables.
                Although the functions for both variables are nearly equivalent,
                best practices dictate using <filename>IMAGE_FEATURES</filename>
                from within a recipe and using
                <filename>EXTRA_IMAGE_FEATURES</filename> from within
                your <filename>local.conf</filename> file, which is found in the
                <link linkend='build-directory'>Build Directory</link>.
            </para>

            <para>
                To understand how these features work, the best reference is
                <filename>meta/classes/core-image.bbclass</filename>.
                This class lists out the available
                <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
                of which most map to package groups while some, such as
                <filename>debug-tweaks</filename> and
                <filename>read-only-rootfs</filename>, resolve as general
                configuration settings.
            </para>

            <para>
                In summary, the file looks at the contents of the
                <filename>IMAGE_FEATURES</filename> variable and then maps
                or configures the feature accordingly.
                Based on this information, the build system automatically
                adds the appropriate packages or configurations to the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'><filename>IMAGE_INSTALL</filename></ulink>
                variable.
                Effectively, you are enabling extra features by extending the
                class or creating a custom class for use with specialized image
                <filename>.bb</filename> files.
            </para>

            <para>
                Use the <filename>EXTRA_IMAGE_FEATURES</filename> variable
                from within your local configuration file.
                Using a separate area from which to enable features with
                this variable helps you avoid overwriting the features in the
                image recipe that are enabled with
                <filename>IMAGE_FEATURES</filename>.
                The value of <filename>EXTRA_IMAGE_FEATURES</filename> is added
                to <filename>IMAGE_FEATURES</filename> within
                <filename>meta/conf/bitbake.conf</filename>.
            </para>

            <para>
                To illustrate how you can use these variables to modify your
                image, consider an example that selects the SSH server.
                The Yocto Project ships with two SSH servers you can use
                with 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 <filename>core-image-sato</filename> image
                is configured to use Dropbear.
                The <filename>core-image-full-cmdline</filename> and
                <filename>core-image-lsb</filename> images both
                include OpenSSH.
                The <filename>core-image-minimal</filename> image does not
                contain an SSH server.
            </para>

            <para>
                You can customize your image and change these defaults.
                Edit the <filename>IMAGE_FEATURES</filename> variable
                in your recipe or use the
                <filename>EXTRA_IMAGE_FEATURES</filename> in your
                <filename>local.conf</filename> file so that it configures the
                image you are working with to include
                <filename>ssh-server-dropbear</filename> or
                <filename>ssh-server-openssh</filename>.
            </para>

            <note>
                See the
                "<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>"
                section in the Yocto Project Reference Manual for a complete
                list of image features that ship with the Yocto Project.
            </note>
        </section>

        <section id='usingpoky-extend-customimage-custombb'>
            <title>Customizing Images Using Custom .bb Files</title>

            <para>
                You can also customize an image by creating a custom recipe
                that defines additional software as part of the image.
                The following example shows the form for the two lines you need:
                <literallayout class='monospaced'>
     IMAGE_INSTALL = "packagegroup-core-x11-base package1 package2"

     inherit core-image
                </literallayout>
            </para>

            <para>
                Defining the software using a custom recipe gives you total
                control over the contents of the image.
                It is important to use the correct names of packages in the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'>IMAGE_INSTALL</ulink></filename>
                variable.
                You must use the OpenEmbedded notation and not the Debian notation for the names
                (e.g. <filename>glibc-dev</filename> instead of <filename>libc6-dev</filename>).
            </para>

            <para>
                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 <filename>core-image-sato</filename>
                but add the additional package <filename>strace</filename> to the image,
                copy the <filename>meta/recipes-sato/images/core-image-sato.bb</filename> to a
                new <filename>.bb</filename> and add the following line to the end of the copy:
                <literallayout class='monospaced'>
     IMAGE_INSTALL += "strace"
                </literallayout>
            </para>
        </section>

        <section id='usingpoky-extend-customimage-customtasks'>
            <title>Customizing Images Using Custom Package Groups</title>

            <para>
                For complex custom images, the best approach for customizing
                an image is to create a custom package group recipe that is
                used to build the image or images.
                A good example of a package group recipe is
                <filename>meta/recipes-core/packagegroups/packagegroup-base.bb</filename>.
            </para>

            <para>
                If you examine that recipe, you see that the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'>PACKAGES</ulink></filename>
                variable lists the package group packages to produce.
                The <filename>inherit packagegroup</filename> statement
                sets appropriate default values and automatically adds
                <filename>-dev</filename>, <filename>-dbg</filename>, and
                <filename>-ptest</filename> complementary packages for each
                package specified in the <filename>PACKAGES</filename>
                statement.
                <note>
                    The <filename>inherit packages</filename> should be
                    located near the top of the recipe, certainly before
                    the <filename>PACKAGES</filename> statement.
                </note>
            </para>

            <para>
                For each package you specify in <filename>PACKAGES</filename>,
                you can use
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'>RDEPENDS</ulink></filename>
                and
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'>RRECOMMENDS</ulink></filename>
                entries to provide a list of packages the parent task package
                should contain.
                You can see examples of these further down in the
                <filename>packagegroup-base.bb</filename> recipe.
            </para>

            <para>
                Here is a short, fabricated example showing the same basic
                pieces:
                <literallayout class='monospaced'>
     DESCRIPTION = "My Custom Package Groups"

     inherit packagegroup

     PACKAGES = "\
         packagegroup-custom-apps \
         packagegroup-custom-tools \
         "

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

     RDEPENDS_packagegroup-custom-tools = "\
         oprofile \
         oprofileui-server \
         lttng-tools"

     RRECOMMENDS_packagegroup-custom-tools = "\
         kernel-module-oprofile"
                </literallayout>
            </para>

            <para>
                In the previous example, two package group packages are created with their dependencies and their
                recommended package dependencies listed: <filename>packagegroup-custom-apps</filename>, and
                <filename>packagegroup-custom-tools</filename>.
                To build an image using these package group packages, you need to add
                <filename>packagegroup-custom-apps</filename> and/or
                <filename>packagegroup-custom-tools</filename> to
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'>IMAGE_INSTALL</ulink></filename>.
                For other forms of image dependencies see the other areas of this section.
            </para>
        </section>

        <section id='usingpoky-extend-customimage-image-name'>
            <title>Customizing an Image Hostname</title>

            <para>
                By default, the configured hostname (i.e.
                <filename>/etc/hostname</filename>) in an image is the
                same as the machine name.
                For example, if
                <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
                equals "qemux86", the configured hostname written to
                <filename>/etc/hostname</filename> is "qemux86".
            </para>

            <para>
                You can customize this name by altering the value of the
                "hostname" variable in the
                <filename>base-files</filename> recipe using either
                an append file or a configuration file.
                Use the following in an append file:
                <literallayout class='monospaced'>
     hostname="myhostname"
                </literallayout>
                Use the following in a configuration file:
                <literallayout class='monospaced'>
     hostname_pn-base-files = "myhostname"
                </literallayout>
            </para>

            <para>
                Changing the default value of the variable "hostname" can be
                useful in certain situations.
                For example, suppose you need to do extensive testing on an
                image and you would like to easily identify the image
                under test from existing images with typical default
                hostnames.
                In this situation, you could change the default hostname to
                "testme", which results in all the images using the name
                "testme".
                Once testing is complete and you do not need to rebuild the
                image for test any longer, you can easily reset the default
                hostname.
            </para>

            <para>
                Another point of interest is that if you unset the variable,
                the image will have no default hostname in the filesystem.
                Here is an example that unsets the variable in a
                configuration file:
                <literallayout class='monospaced'>
     hostname_pn-base-files = ""
                </literallayout>
                Having no default hostname in the filesystem is suitable for
                environments that use dynamic hostnames such as virtual
                machines.
            </para>
        </section>
    </section>

    <section id='new-recipe-writing-a-new-recipe'>
        <title>Writing a New Recipe</title>

        <para>
            Recipes (<filename>.bb</filename> files) are fundamental components
            in the Yocto Project environment.
            Each software component built by the OpenEmbedded build system
            requires a recipe to define the component.
            This section describes how to create, write, and test a new
            recipe.
            <note>
                For information on variables that are useful for recipes and
                for information about recipe naming issues, see the
                "<ulink url='&YOCTO_DOCS_REF_URL;#ref-varlocality-recipe-required'>Required</ulink>"
                section of the Yocto Project Reference Manual.
            </note>
        </para>

        <section id='new-recipe-overview'>
            <title>Overview</title>

            <para>
                The following figure shows the basic process for creating a
                new recipe.
                The remainder of the section provides details for the steps.
                <imagedata fileref="figures/recipe-workflow.png" width="6in" depth="7in" align="center" scalefit="1" />
            </para>
        </section>

        <section id='new-recipe-locate-or-automatically-create-a-base-recipe'>
            <title>Locate or Automatically Create a Base Recipe</title>

            <para>
                You can always write a recipe from scratch.
                However, two choices exist that can help you quickly get a
                start on a new recipe:
                <itemizedlist>
                    <listitem><para><emphasis><filename>recipetool</filename>:</emphasis>
                        A tool provided by the Yocto Project that automates
                        creation of a base recipe based on the source
                        files.
                        </para></listitem>
                    <listitem><para><emphasis>Existing Recipes:</emphasis>
                        Location and modification of an existing recipe that is
                        similar in function to the recipe you need.
                        </para></listitem>
                </itemizedlist>
            </para>

            <section id='new-recipe-creating-the-base-recipe-using-recipetool'>
                <title>Creating the Base Recipe Using <filename>recipetool</filename></title>

                <para>
                    <filename>recipetool</filename> automates creation of
                    a base recipe given a set of source code files.
                    As long as you can extract or point to the source files,
                    the tool will construct a recipe and automatically
                    configure all pre-build information into the recipe.
                    For example, suppose you have an application that builds
                    using Autotools.
                    Creating the base recipe using
                    <filename>recipetool</filename> results in a recipe
                    that has the pre-build dependencies, license requirements,
                    and checksums configured.
                </para>

                <para>
                    To run the tool, you just need to be in your
                    <link linkend='build-directory'>Build Directory</link>
                    and have sourced the build environment setup script
                    (i.e.
                    <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>oe-init-build-env</filename></ulink>
                    or
                    <ulink url='&YOCTO_DOCS_REF_URL;#structure-memres-core-script'><filename>oe-init-build-env-memres</filename></ulink>).
                    Here is the basic <filename>recipetool</filename> syntax:
                    <note>
                        Running <filename>recipetool -h</filename> or
                        <filename>recipetool create -h</filename> produces the
                        Python-generated help, which presented differently
                        than what follows here.
                    </note>
                    <literallayout class='monospaced'>
     recipetool -h
     recipetool create [-h]
     recipetool [-d] [-q] [--color auto | always | never ] create -o <replaceable>OUTFILE</replaceable> [-m] [-x <replaceable>EXTERNALSRC</replaceable>] <replaceable>source</replaceable>

          -d       Enables debug output.
          -q       Outputs only errors (quiet mode).
          --color  Colorizes the output automatically, always, or never.
          -h       Displays Python generated syntax for recipetool.
          create   Causes recipetool to create a base recipe.  The create
                   command is further defined with these options:

                   -o <replaceable>OUTFILE</replaceable>      Specifies the full path and filename for the generated
                                   recipe.
                   -m              Causes the recipe to be machine-specific rather than
                                   architecture-specific (default).
                   -x <replaceable>EXTERNALSRC</replaceable>  Fetches and extracts source files from <replaceable>source</replaceable>
                                   and places them in <replaceable>EXTERNALSRC</replaceable>.
                                   <replaceable>source</replaceable> must be a URL.
                   -h              Displays Python-generated syntax for create.
                   <replaceable>source</replaceable>          Specifies the source code on which to base the
                                   recipe.
                    </literallayout>
                </para>

                <para>
                    Running <filename>recipetool create -o</filename>&nbsp;<replaceable>OUTFILE</replaceable>
                    creates the base recipe and locates it properly in the
                    layer that contains your source files.
                    Following are some syntax examples:
                </para>

                <para>
                    Use this syntax to generate a recipe based on <replaceable>source</replaceable>.
                    Once generated, the recipe resides in the existing source
                    code layer:
                    <literallayout class='monospaced'>
     recipetool create -o <replaceable>OUTFILE</replaceable>&nbsp;<replaceable>source</replaceable>
                    </literallayout>
                    Use this syntax to generate a recipe using code that you
                    extract from <replaceable>source</replaceable>.
                    The extracted code is placed in its own layer defined
                    by <replaceable>EXTERNALSRC</replaceable>.
                    <literallayout class='monospaced'>
     recipetool create -o <replaceable>OUTFILE</replaceable> -x <replaceable>EXTERNALSRC</replaceable> <replaceable>source</replaceable>
                    </literallayout>
                    Use this syntax to generate a recipe based on <replaceable>source</replaceable>.
                    The options direct <filename>recipetool</filename> to
                    run in "quiet mode" and to generate debugging information.
                    Once generated, the recipe resides in the existing source
                    code layer:
                    <literallayout class='monospaced'>
     recipetool create -o <replaceable>OUTFILE</replaceable> <replaceable>source</replaceable>
                    </literallayout>
                </para>
            </section>

            <section id='new-recipe-locating-and-using-a-similar-recipe'>
                <title>Locating and Using a Similar Recipe</title>

                <para>
                    Before writing a recipe from scratch, it is often useful to
                    discover whether someone else has already written one that
                    meets (or comes close to meeting) your needs.
                    The Yocto Project and OpenEmbedded communities maintain many
                    recipes that might be candidates for what you are doing.
                    You can find a good central index of these recipes in the
                    <ulink url='http://layers.openembedded.org'>OpenEmbedded metadata index</ulink>.
                </para>

                <para>
                    Working from an existing recipe or a skeleton recipe is the
                    best way to get started.
                    Here are some points on both methods:
                    <itemizedlist>
                        <listitem><para><emphasis>Locate and modify a recipe that
                            is close to what you want to do:</emphasis>
                            This method works when you are familiar with the
                            current recipe space.
                            The method does not work so well for those new to
                            the Yocto Project or writing recipes.</para>
                            <para>Some risks associated with this method are
                            using a recipe that has areas totally unrelated to
                            what you are trying to accomplish with your recipe,
                            not recognizing areas of the recipe that you might
                            have to add from scratch, and so forth.
                            All these risks stem from unfamiliarity with the
                            existing recipe space.</para></listitem>
                        <listitem><para><emphasis>Use and modify the following
                            skeleton recipe:</emphasis>
                            If for some reason you do not want to use
                            <filename>recipetool</filename> and you cannot
                            find an existing recipe that is close to meeting
                            your needs, you can use the following structure to
                            provide the fundamental areas of a new recipe.
                            <literallayout class='monospaced'>
     DESCRIPTION = ""
     HOMEPAGE = ""
     LICENSE = ""
     SECTION = ""
     DEPENDS = ""
     LIC_FILES_CHKSUM = ""

     SRC_URI = ""
                            </literallayout>
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>
        </section>

        <section id='new-recipe-storing-and-naming-the-recipe'>
            <title>Storing and Naming the Recipe</title>

            <para>
                Once you have your base recipe, you should put it in your
                own layer and name it appropriately.
                Locating it correctly ensures that the OpenEmbedded build
                system can find it when you use BitBake to process the
                recipe.
            </para>

            <itemizedlist>
                <listitem><para><emphasis>Storing Your Recipe:</emphasis>
                    The OpenEmbedded build system locates your recipe
                    through the layer's <filename>conf/layer.conf</filename>
                    file and the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILES'><filename>BBFILES</filename></ulink>
                    variable.
                    This variable sets up a path from which the build system can
                    locate recipes.
                    Here is the typical use:
                    <literallayout class='monospaced'>
     BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
                 ${LAYERDIR}/recipes-*/*/*.bbappend"
                    </literallayout>
                    Consequently, you need to be sure you locate your new recipe
                    inside your layer such that it can be found.</para>
                    <para>You can find more information on how layers are
                    structured in the
                    "<link linkend='understanding-and-creating-layers'>Understanding and Creating Layers</link>"
                    section.</para></listitem>
                <listitem><para><emphasis>Naming Your Recipe:</emphasis>
                    When you name your recipe, you need to follow this naming
                    convention:
                    <literallayout class='monospaced'>
     <replaceable>basename</replaceable>_<replaceable>version</replaceable>.bb
                    </literallayout>
                    Use lower-cased characters and do not include the reserved
                    suffixes <filename>-native</filename>,
                    <filename>-cross</filename>, <filename>-initial</filename>,
                    or <filename>-dev</filename> casually (i.e. do not use them
                    as part of your recipe name unless the string applies).
                    Here are some examples:
                    <literallayout class='monospaced'>
     cups_1.7.0.bb
     gawk_4.0.2.bb
     irssi_0.8.16-rc1.bb
                    </literallayout></para></listitem>
            </itemizedlist>
        </section>

        <section id='understanding-recipe-syntax'>
            <title>Understanding Recipe Syntax</title>

            <para>
                Understanding recipe file syntax is important for
                writing recipes.
                The following list overviews the basic items that make up a
                BitBake recipe file.
                For more complete BitBake syntax descriptions, see the
                "<ulink url='&YOCTO_DOCS_BB_URL;#bitbake-user-manual-metadata'>Syntax and Operators</ulink>"
                chapter of the BitBake User Manual.
                <itemizedlist>
                    <listitem><para><emphasis>Variable Assignments and Manipulations:</emphasis>
                        Variable assignments allow a value to be assigned to a
                        variable.
                        The assignment can be static text or might include
                        the contents of other variables.
                        In addition to the assignment, appending and prepending
                        operations are also supported.</para>
                        <para>The following example shows some of the ways
                        you can use variables in recipes:
                        <literallayout class='monospaced'>
     S = "${WORKDIR}/postfix-${PV}"
     CFLAGS += "-DNO_ASM"
     SRC_URI_append = " file://fixup.patch"
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Functions:</emphasis>
                        Functions provide a series of actions to be performed.
                        You usually use functions to override the default
                        implementation of a task function or to complement
                        a default function (i.e. append or prepend to an
                        existing function).
                        Standard functions use <filename>sh</filename> shell
                        syntax, although access to OpenEmbedded variables and
                        internal methods are also available.</para>
                        <para>The following is an example function from the
                        <filename>sed</filename> recipe:
                        <literallayout class='monospaced'>
     do_install () {
         autotools_do_install
         install -d ${D}${base_bindir}
         mv ${D}${bindir}/sed ${D}${base_bindir}/sed
         rmdir ${D}${bindir}/
     }
                        </literallayout>
                        It is also possible to implement new functions that
                        are called between existing tasks as long as the
                        new functions are not replacing or complementing the
                        default functions.
                        You can implement functions in Python
                        instead of shell.
                        Both of these options are not seen in the majority of
                        recipes.</para></listitem>
                    <listitem><para><emphasis>Keywords:</emphasis>
                        BitBake recipes use only a few keywords.
                        You use keywords to include common
                        functions (<filename>inherit</filename>), load parts
                        of a recipe from other files
                        (<filename>include</filename> and
                        <filename>require</filename>) and export variables
                        to the environment (<filename>export</filename>).</para>
                        <para>The following example shows the use of some of
                        these keywords:
                        <literallayout class='monospaced'>
     export POSTCONF = "${STAGING_BINDIR}/postconf"
     inherit autoconf
     require otherfile.inc
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Comments:</emphasis>
                        Any lines that begin with the hash character
                        (<filename>#</filename>) are treated as comment lines
                        and are ignored:
                        <literallayout class='monospaced'>
     # This is a comment
                        </literallayout>
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                This next list summarizes the most important and most commonly
                used parts of the recipe syntax.
                For more information on these parts of the syntax, you can
                reference the
                <ulink url='&YOCTO_DOCS_BB_URL;#bitbake-user-manual-metadata'>Syntax and Operators</ulink>
                chapter in the BitBake User Manual.
                <itemizedlist>
                    <listitem><para><emphasis>Line Continuation: <filename>\</filename></emphasis> -
                        Use the backward slash (<filename>\</filename>)
                        character to split a statement over multiple lines.
                        Place the slash character at the end of the line that
                        is to be continued on the next line:
                        <literallayout class='monospaced'>
     VAR = "A really long \
            line"
                        </literallayout>
                        <note>
                            You cannot have any characters including spaces
                            or tabs after the slash character.
                        </note>
                        </para></listitem>
                    <listitem><para><emphasis>Using Variables: <filename>${...}</filename></emphasis> -
                        Use the <filename>${<replaceable>VARNAME</replaceable>}</filename> syntax to
                        access the contents of a variable:
                        <literallayout class='monospaced'>
     SRC_URI = "${SOURCEFORGE_MIRROR}/libpng/zlib-${PV}.tar.gz"
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Quote All Assignments: <filename>"<replaceable>value</replaceable>"</filename></emphasis> -
                        Use double quotes around the value in all variable
                        assignments.
                        <literallayout class='monospaced'>
     VAR1 = "${OTHERVAR}"
     VAR2 = "The version is ${PV}"
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Conditional Assignment: <filename>?=</filename></emphasis> -
                        Conditional assignment is used to assign a value to
                        a variable, but only when the variable is currently
                        unset.
                        Use the question mark followed by the equal sign
                        (<filename>?=</filename>) to make a "soft" assignment
                        used for conditional assignment.
                        Typically, "soft" assignments are used in the
                        <filename>local.conf</filename> file for variables
                        that are allowed to come through from the external
                        environment.
                        </para>
                        <para>Here is an example where
                        <filename>VAR1</filename> is set to "New value" if
                        it is currently empty.
                        However, if <filename>VAR1</filename> has already been
                        set, it remains unchanged:
                        <literallayout class='monospaced'>
     VAR1 ?= "New value"
                        </literallayout>
                        In this next example, <filename>VAR1</filename>
                        is left with the value "Original value":
                        <literallayout class='monospaced'>
     VAR1 = "Original value"
     VAR1 ?= "New value"
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Appending: <filename>+=</filename></emphasis> -
                        Use the plus character followed by the equals sign
                        (<filename>+=</filename>) to append values to existing
                        variables.
                        <note>
                            This operator adds a space between the existing
                            content of the variable and the new content.
                        </note></para>
                        <para>Here is an example:
                        <literallayout class='monospaced'>
     SRC_URI += "file://fix-makefile.patch"
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Prepending: <filename>=+</filename></emphasis> -
                        Use the equals sign followed by the plus character
                        (<filename>=+</filename>) to prepend values to existing
                        variables.
                        <note>
                            This operator adds a space between the new content
                            and the existing content of the variable.
                        </note></para>
                        <para>Here is an example:
                        <literallayout class='monospaced'>
     VAR =+ "Starts"
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Appending: <filename>_append</filename></emphasis> -
                        Use the <filename>_append</filename> operator to
                        append values to existing variables.
                        This operator does not add any additional space.
                        Also, the operator is applied after all the
                        <filename>+=</filename>, and
                        <filename>=+</filename> operators have been applied and
                        after all <filename>=</filename> assignments have
                        occurred.
                        </para>
                        <para>The following example shows the space being
                        explicitly added to the start to ensure the appended
                        value is not merged with the existing value:
                        <literallayout class='monospaced'>
     SRC_URI_append = " file://fix-makefile.patch"
                        </literallayout>
                        You can also use the <filename>_append</filename>
                        operator with overrides, which results in the actions
                        only being performed for the specified target or
                        machine:
                        <literallayout class='monospaced'>
     SRC_URI_append_sh4 = " file://fix-makefile.patch"
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Prepending: <filename>_prepend</filename></emphasis> -
                        Use the <filename>_prepend</filename> operator to
                        prepend values to existing variables.
                        This operator does not add any additional space.
                        Also, the operator is applied after all the
                        <filename>+=</filename>, and
                        <filename>=+</filename> operators have been applied and
                        after all <filename>=</filename> assignments have
                        occurred.
                        </para>
                        <para>The following example shows the space being
                        explicitly added to the end to ensure the prepended
                        value is not merged with the existing value:
                        <literallayout class='monospaced'>
     CFLAGS_prepend = "-I${S}/myincludes "
                        </literallayout>
                        You can also use the <filename>_prepend</filename>
                        operator with overrides, which results in the actions
                        only being performed for the specified target or
                        machine:
                        <literallayout class='monospaced'>
     CFLAGS_prepend_sh4 = "-I${S}/myincludes "
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Overrides:</emphasis> -
                        You can use overrides to set a value conditionally,
                        typically based on how the recipe is being built.
                        For example, to set the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-KBRANCH'><filename>KBRANCH</filename></ulink>
                        variable's value to "standard/base" for any target
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>,
                        except for qemuarm where it should be set to
                        "standard/arm-versatile-926ejs", you would do the
                        following:
                        <literallayout class='monospaced'>
     KBRANCH = "standard/base"
     KBRANCH_qemuarm  = "standard/arm-versatile-926ejs"
                        </literallayout>
                        Overrides are also used to separate alternate values
                        of a variable in other situations.
                        For example, when setting variables such as
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES</filename></ulink>
                        and
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>
                        that are specific to individual packages produced by
                        a recipe, you should always use an override that
                        specifies the name of the package.
                        </para></listitem>
                    <listitem><para><emphasis>Indentation:</emphasis>
                        Use spaces for indentation rather than than tabs.
                        For shell functions, both currently work.
                        However, it is a policy decision of the Yocto Project
                        to use tabs in shell functions.
                        Realize that some layers have a policy to use spaces
                        for all indentation.
                        </para></listitem>
                    <listitem><para><emphasis>Using Python for Complex Operations: <filename>${@<replaceable>python_code</replaceable>}</filename></emphasis> -
                        For more advanced processing, it is possible to use
                        Python code during variable assignments (e.g.
                        search and replacement on a variable).</para>
                        <para>You indicate Python code using the
                        <filename>${@<replaceable>python_code</replaceable>}</filename>
                        syntax for the variable assignment:
                        <literallayout class='monospaced'>
     SRC_URI = "ftp://ftp.info-zip.org/pub/infozip/src/zip${@d.getVar('PV',1).replace('.', '')}.tgz
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Shell Function Syntax:</emphasis>
                        Write shell functions as if you were writing a shell
                        script when you describe a list of actions to take.
                        You should ensure that your script works with a generic
                        <filename>sh</filename> and that it does not require
                        any <filename>bash</filename> or other shell-specific
                        functionality.
                        The same considerations apply to various system
                        utilities (e.g. <filename>sed</filename>,
                        <filename>grep</filename>, <filename>awk</filename>,
                        and so forth) that you might wish to use.
                        If in doubt, you should check with multiple
                        implementations - including those from BusyBox.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='new-recipe-running-a-build-on-the-recipe'>
            <title>Running a Build on the Recipe</title>

            <para>
                Creating a new recipe is usually an iterative process that
                requires using BitBake to process the recipe multiple times in
                order to progressively discover and add information to the
                recipe file.
            </para>

            <para>
                Assuming you have sourced a build environment setup 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>)
                and you are in the
                <link linkend='build-directory'>Build Directory</link>,
                use BitBake to process your recipe.
                All you need to provide is the
                <filename><replaceable>basename</replaceable></filename> of the recipe as described
                in the previous section:
                <literallayout class='monospaced'>
     $ bitbake <replaceable>basename</replaceable>
                </literallayout>

            </para>

            <para>
                During the build, the OpenEmbedded build system creates a
                temporary work directory for each recipe
                (<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink><filename>}</filename>)
                where it keeps extracted source files, log files, intermediate
                compilation and packaging files, and so forth.
            </para>

            <para>
                The per-recipe temporary work directory is constructed as follows and
                depends on several factors:
                <literallayout class='monospaced'>
     BASE_WORKDIR ?= "${TMPDIR}/work"
     WORKDIR = "${BASE_WORKDIR}/${MULTIMACH_TARGET_SYS}/${PN}/${EXTENDPE}${PV}-${PR}"
                </literallayout>
                As an example, assume a Source Directory top-level folder named
                <filename>poky</filename>, a default Build Directory at
                <filename>poky/build</filename>, and a
                <filename>qemux86-poky-linux</filename> machine target system.
                Furthermore, suppose your recipe is named
                <filename>foo_1.3.0.bb</filename>.
                In this case, the work directory the build system uses to
                build the package would be as follows:
                <literallayout class='monospaced'>
     poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0
                </literallayout>
                Inside this directory you can find sub-directories such as
                <filename>image</filename>, <filename>packages-split</filename>,
                and <filename>temp</filename>.
                After the build, you can examine these to determine how well
                the build went.
                <note>
                    You can find log files for each task in the recipe's
                    <filename>temp</filename> directory (e.g.
                    <filename>poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0/temp</filename>).
                    Log files are named <filename>log.<replaceable>taskname</replaceable></filename>
                    (e.g. <filename>log.do_configure</filename>,
                    <filename>log.do_fetch</filename>, and
                    <filename>log.do_compile</filename>).
                </note>
            </para>

            <para>
                You can find more information about the build process in the
                "<ulink url='&YOCTO_DOCS_REF_URL;#closer-look'>A Closer Look at the Yocto Project Development Environment</ulink>"
                chapter of the Yocto Project Reference Manual.
            </para>

            <para>
                You can also reference the following variables in the
                Yocto Project Reference Manual's glossary for more information:
                <itemizedlist>
                    <listitem><ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>:
                        The top-level build output directory</listitem>
                    <listitem><ulink url='&YOCTO_DOCS_REF_URL;#var-MULTIMACH_TARGET_SYS'><filename>MULTIMACH_TARGET_SYS</filename></ulink>:
                        The target system identifier</listitem>
                    <listitem><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink>:
                        The recipe name</listitem>
                    <listitem><ulink url='&YOCTO_DOCS_REF_URL;#var-EXTENDPE'><filename>EXTENDPE</filename></ulink>:
                        The epoch - (if
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PE'><filename>PE</filename></ulink>
                        is not specified, which is usually the case for most
                        recipes, then <filename>EXTENDPE</filename> is blank)</listitem>
                    <listitem><ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>:
                        The recipe version</listitem>
                    <listitem><ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>:
                        The recipe revision</listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='new-recipe-fetching-code'>
            <title>Fetching Code</title>

            <para>
                The first thing your recipe must do is specify how to fetch
                the source files.
                Fetching is controlled mainly through the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                variable.
                Your recipe must have a <filename>SRC_URI</filename> variable
                that points to where the source is located.
                For a graphical representation of source locations, see the
                "<ulink url='&YOCTO_DOCS_REF_URL;#sources-dev-environment'>Sources</ulink>"
                section in the Yocto Project Reference Manual.
            </para>

            <para>
                The
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-fetch'><filename>do_fetch</filename></ulink>
                task uses the prefix of each entry in the
                <filename>SRC_URI</filename> variable value to determine which
                fetcher to use to get your source files.
                It is the <filename>SRC_URI</filename> variable that triggers
                the fetcher.
                The
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-patch'><filename>do_patch</filename></ulink>
                task uses the variable after source is fetched to apply
                patches.
                The OpenEmbedded build system uses
                <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESOVERRIDES'><filename>FILESOVERRIDES</filename></ulink>
                for scanning directory locations for local files in
                <filename>SRC_URI</filename>.
            </para>

            <para>
                The <filename>SRC_URI</filename> variable in your recipe must
                define each unique location for your source files.
                It is good practice to not hard-code pathnames in an URL used
                in <filename>SRC_URI</filename>.
                Rather than hard-code these paths, use
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink><filename>}</filename>,
                which causes the fetch process to use the version specified in
                the recipe filename.
                Specifying the version in this manner means that upgrading the
                recipe to a future version is as simple as renaming the recipe
                to match the new version.
            </para>

            <para>
                Here is a simple example from the
                <filename>meta/recipes-devtools/cdrtools/cdrtools-native_3.01a20.bb</filename>
                recipe where the source comes from a single tarball.
                Notice the use of the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
                variable:
                <literallayout class='monospaced'>
     SRC_URI = "ftp://ftp.berlios.de/pub/cdrecord/alpha/cdrtools-${PV}.tar.bz2"
                </literallayout>
            </para>

            <para>
                Files mentioned in <filename>SRC_URI</filename> whose names end
                in a typical archive extension (e.g. <filename>.tar</filename>,
                <filename>.tar.gz</filename>, <filename>.tar.bz2</filename>,
                <filename>.zip</filename>, and so forth), are automatically
                extracted during the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-unpack'><filename>do_unpack</filename></ulink>
                task.
                For another example that specifies these types of files, see
                the
                "<link linkend='new-recipe-autotooled-package'>Autotooled Package</link>"
                section.
            </para>

            <para>
                Another way of specifying source is from an SCM.
                For Git repositories, you must specify
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRCREV'><filename>SRCREV</filename></ulink>
                and you should specify
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
                to include the revision with
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRCPV'><filename>SRCPV</filename></ulink>.
                Here is an example from the recipe
                <filename>meta/recipes-kernel/blktrace/blktrace_git.bb</filename>:
                <literallayout class='monospaced'>
     SRCREV = "d6918c8832793b4205ed3bfede78c2f915c23385"

     PR = "r6"
     PV = "1.0.5+git${SRCPV}"

     SRC_URI = "git://git.kernel.dk/blktrace.git \
                file://ldflags.patch"
                </literallayout>
            </para>

            <para>
                If your <filename>SRC_URI</filename> statement includes
                URLs pointing to individual files fetched from a remote server
                other than a version control system, BitBake attempts to
                verify the files against checksums defined in your recipe to
                ensure they have not been tampered with or otherwise modified
                since the recipe was written.
                Two checksums are used:
                <filename>SRC_URI[md5sum]</filename> and
                <filename>SRC_URI[sha256sum]</filename>.
            </para>

            <para>
                If your <filename>SRC_URI</filename> variable points to
                more than a single URL (excluding SCM URLs), you need to
                provide the <filename>md5</filename> and
                <filename>sha256</filename> checksums for each URL.
                For these cases, you provide a name for each URL as part of
                the <filename>SRC_URI</filename> and then reference that name
                in the subsequent checksum statements.
                Here is an example:
                <literallayout class='monospaced'>
     SRC_URI = "${DEBIAN_MIRROR}/main/a/apmd/apmd_3.2.2.orig.tar.gz;name=tarball \
                ${DEBIAN_MIRROR}/main/a/apmd/apmd_${PV}.diff.gz;name=patch

     SRC_URI[tarball.md5sum] = "b1e6309e8331e0f4e6efd311c2d97fa8"
     SRC_URI[tarball.sha256sum] = "7f7d9f60b7766b852881d40b8ff91d8e39fccb0d1d913102a5c75a2dbb52332d"

     SRC_URI[patch.md5sum] = "57e1b689264ea80f78353519eece0c92"
     SRC_URI[patch.sha256sum] = "7905ff96be93d725544d0040e425c42f9c05580db3c272f11cff75b9aa89d430"
                </literallayout>
            </para>

            <para>
                Proper values for <filename>md5</filename> and
                <filename>sha256</filename> checksums might be available
                with other signatures on the download page for the upstream
                source (e.g. <filename>md5</filename>,
                <filename>sha1</filename>, <filename>sha256</filename>,
                <filename>GPG</filename>, and so forth).
                Because the OpenEmbedded build system only deals with
                <filename>sha256sum</filename> and <filename>md5sum</filename>,
                you should verify all the signatures you find by hand.
            </para>

            <para>
                If no <filename>SRC_URI</filename> checksums are specified
                when you attempt to build the recipe, or you provide an
                incorrect checksum, the build will produce an error for each
                missing or incorrect checksum.
                As part of the error message, the build system provides
                the checksum string corresponding to the fetched file.
                Once you have the correct checksums, you can copy and paste
                them into your recipe and then run the build again to continue.
                <note>
                    As mentioned, if the upstream source provides signatures
                    for verifying the downloaded source code, you should
                    verify those manually before setting the checksum values
                    in the recipe and continuing with the build.
                </note>
            </para>

            <para>
                This final example is a bit more complicated and is from the
                <filename>meta/recipes-sato/rxvt-unicode/rxvt-unicode_9.20.bb</filename>
                recipe.
                The example's <filename>SRC_URI</filename> statement identifies
                multiple files as the source files for the recipe: a tarball, a
                patch file, a desktop file, and an icon.
                <literallayout class='monospaced'>
     SRC_URI = "http://dist.schmorp.de/rxvt-unicode/Attic/rxvt-unicode-${PV}.tar.bz2 \
                file://xwc.patch \
                file://rxvt.desktop \
                file://rxvt.png"
                </literallayout>
            </para>

            <para>
                When you specify local files using the
                <filename>file://</filename> URI protocol, the build system
                fetches files from the local machine.
                The path is relative to the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink>
                variable and searches specific directories in a certain order:
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BP'><filename>BP</filename></ulink><filename>}</filename>,
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BPN'><filename>BPN</filename></ulink><filename>}</filename>,
                and <filename>files</filename>.
                The directories are assumed to be subdirectories of the
                directory in which the recipe or append file resides.
                For another example that specifies these types of files, see the
                "<link linkend='new-recipe-single-c-file-package-hello-world'>Single .c File Package (Hello World!)</link>"
                section.
            </para>

            <para>
                The previous example also specifies a patch file.
                Patch files are files whose names usually end in
                <filename>.patch</filename> or <filename>.diff</filename> but
                can end with compressed suffixes such as
                <filename>diff.gz</filename> and
                <filename>patch.bz2</filename>, for example.
                The build system automatically applies patches as described
                in the
                "<link linkend='new-recipe-patching-code'>Patching Code</link>" section.
            </para>
        </section>

        <section id='new-recipe-unpacking-code'>
            <title>Unpacking Code</title>

            <para>
                During the build, the
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-unpack'><filename>do_unpack</filename></ulink>
                task unpacks the source with
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink><filename>}</filename>
                pointing to where it is unpacked.
            </para>

            <para>
                If you are fetching your source files from an upstream source
                archived tarball and the tarball's internal structure matches
                the common convention of a top-level subdirectory named
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BPN'><filename>BPN</filename></ulink><filename>}-${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink><filename>}</filename>,
                then you do not need to set <filename>S</filename>.
                However, if <filename>SRC_URI</filename> specifies to fetch
                source from an archive that does not use this convention,
                or from an SCM like Git or Subversion, your recipe needs to
                define <filename>S</filename>.
            </para>

            <para>
                If processing your recipe using BitBake successfully unpacks
                the source files, you need to be sure that the directory
                pointed to by <filename>${S}</filename> matches the structure
                of the source.
            </para>
        </section>

        <section id='new-recipe-patching-code'>
            <title>Patching Code</title>

            <para>
                Sometimes it is necessary to patch code after it has been
                fetched.
                Any files mentioned in <filename>SRC_URI</filename> whose
                names end in <filename>.patch</filename> or
                <filename>.diff</filename> or compressed versions of these
                suffixes (e.g. <filename>diff.gz</filename> are treated as
                patches.
                The
                <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-patch'><filename>do_patch</filename></ulink>
                task automatically applies these patches.
            </para>

            <para>
                The build system should be able to apply patches with the "-p1"
                option (i.e. one directory level in the path will be stripped
                off).
                If your patch needs to have more directory levels stripped off,
                specify the number of levels using the "striplevel" option in
                the <filename>SRC_URI</filename> entry for the patch.
                Alternatively, if your patch needs to be applied in a specific
                subdirectory that is not specified in the patch file, use the
                "patchdir" option in the entry.
            </para>

            <para>
                As with all local files referenced in
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                using <filename>file://</filename>, you should place
                patch files in a directory next to the recipe either
                named the same as the base name of the recipe
                (<ulink url='&YOCTO_DOCS_REF_URL;#var-BP'><filename>BP</filename></ulink>
                and
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BPN'><filename>BPN</filename></ulink>)
                or "files".
            </para>
        </section>

        <section id='new-recipe-licensing'>
            <title>Licensing</title>

            <para>
                Your recipe needs to have both the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE'><filename>LICENSE</filename></ulink>
                and
                <ulink url='&YOCTO_DOCS_REF_URL;#var-LIC_FILES_CHKSUM'><filename>LIC_FILES_CHKSUM</filename></ulink>
                variables:
                <itemizedlist>
                    <listitem><para><emphasis><filename>LICENSE</filename>:</emphasis>
                        This variable specifies the license for the software.
                        If you do not know the license under which the software
                        you are building is distributed, you should go to the
                        source code and look for that information.
                        Typical files containing this information include
                        <filename>COPYING</filename>,
                        <filename>LICENSE</filename>, and
                        <filename>README</filename> files.
                        You could also find the information near the top of
                        a source file.
                        For example, given a piece of software licensed under
                        the GNU General Public License version 2, you would
                        set <filename>LICENSE</filename> as follows:
                        <literallayout class='monospaced'>
     LICENSE = "GPLv2"
                        </literallayout></para>
                        <para>The licenses you specify within
                        <filename>LICENSE</filename> can have any name as long
                        as you do not use spaces, since spaces are used as
                        separators between license names.
                        For standard licenses, use the names of the files in
                        <filename>meta/files/common-licenses/</filename>
                        or the <filename>SPDXLICENSEMAP</filename> flag names
                        defined in <filename>meta/conf/licenses.conf</filename>.
                        </para></listitem>
                    <listitem><para><emphasis><filename>LIC_FILES_CHKSUM</filename>:</emphasis>
                        The OpenEmbedded build system uses this variable to
                        make sure the license text has not changed.
                        If it has, the build produces an error and it affords
                        you the chance to figure it out and correct the problem.
                        </para>
                        <para>You need to specify all applicable licensing
                        files for the software.
                        At the end of the configuration step, the build process
                        will compare the checksums of the files to be sure
                        the text has not changed.
                        Any differences result in an error with the message
                        containing the current checksum.
                        For more explanation and examples of how to set the
                        <filename>LIC_FILES_CHKSUM</filename> variable, see the
                        "<ulink url='&YOCTO_DOCS_REF_URL;#usingpoky-configuring-LIC_FILES_CHKSUM'>Tracking License Changes</ulink>"
                        section in the Yocto Project Reference Manual.</para>
                        <para>To determine the correct checksum string, you
                        can list the appropriate files in the
                        <filename>LIC_FILES_CHKSUM</filename> variable with
                        incorrect md5 strings, attempt to build the software,
                        and then note the resulting error messages that will
                        report the correct md5 strings.
                        See the
                        "<link linkend='new-recipe-fetching-code'>Fetching Code</link>"
                        section for additional information.
                    </para>

                    <para>
                        Here is an example that assumes the software has a
                        <filename>COPYING</filename> file:
                        <literallayout class='monospaced'>
     LIC_FILES_CHKSUM = "file://COPYING;md5=xxx"
                        </literallayout>
                        When you try to build the software, the build system
                        will produce an error and give you the correct string
                        that you can substitute into the recipe file for a
                        subsequent build.
                        </para></listitem>
                </itemizedlist>
            </para>

<!--

            <para>
                For trying this out I created a new recipe named
                <filename>htop_1.0.2.bb</filename> and put it in
                <filename>poky/meta/recipes-extended/htop</filename>.
                There are two license type statements in my very simple
                recipe:
                <literallayout class='monospaced'>
     LICENSE = ""

     LIC_FILES_CHKSUM = ""

     SRC_URI[md5sum] = ""
     SRC_URI[sha256sum] = ""
                </literallayout>
                Evidently, you need to run a <filename>bitbake -c cleanall htop</filename>.
                Next, you delete or comment out the two <filename>SRC_URI</filename>
                lines at the end and then attempt to build the software with
                <filename>bitbake htop</filename>.
                Doing so causes BitBake to report some errors and and give
                you the actual strings you need for the last two
                <filename>SRC_URI</filename> lines.
                Prior to this, you have to dig around in the home page of the
                source for <filename>htop</filename> and determine that the
                software is released under GPLv2.
                You can provide that in the <filename>LICENSE</filename>
                statement.
                Now you edit your recipe to have those two strings for
                the <filename>SRC_URI</filename> statements:
                <literallayout class='monospaced'>
     LICENSE = "GPLv2"

     LIC_FILES_CHKSUM = ""

     SRC_URI = "${SOURCEFORGE_MIRROR}/htop/htop-${PV}.tar.gz"
     SRC_URI[md5sum] = "0d01cca8df3349c74569cefebbd9919e"
     SRC_URI[sha256sum] = "ee60657b044ece0df096c053060df7abf3cce3a568ab34d260049e6a37ccd8a1"
                </literallayout>
                At this point, you can build the software again using the
                <filename>bitbake htop</filename> command.
                There is just a set of errors now associated with the
                empty <filename>LIC_FILES_CHKSUM</filename> variable now.
            </para>
-->

        </section>

        <section id='new-recipe-configuring-the-recipe'>
            <title>Configuring the Recipe</title>

            <para>
                Most software provides some means of setting build-time
                configuration options before compilation.
                Typically, setting these options is accomplished by running a
                configure script with some options, or by modifying a build
                configuration file.
                <note>
                    As of Yocto Project Release 7.1, some of the core recipes
                    that package binary configuration scripts now disable the
                    scripts due to the scripts previously requiring error-prone
                    path substitution.
                    The OpenEmbedded build system uses
                    <filename>pkg-config</filename> now, which is much more
                    robust.
                    You can find a list of the <filename>*-config</filename>
                    scripts that are disabled list in the
                    "<ulink url='&YOCTO_DOCS_REF_URL;#migration-1.7-binary-configuration-scripts-disabled'>Binary Configuration Scripts Disabled</ulink>"
                    section in the Yocto Project Reference Manual.
                </note>
            </para>

            <para>
                A major part of build-time configuration is about checking for
                build-time dependencies and possibly enabling optional
                functionality as a result.
                You need to specify any build-time dependencies for the
                software you are building in your recipe's
                <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
                value, in terms of other recipes that satisfy those
                dependencies.
                You can often find build-time or runtime
                dependencies described in the software's documentation.
            </para>

            <para>
                The following list provides configuration items of note based
                on how your software is built:
                <itemizedlist>
                    <listitem><para><emphasis>Autotools:</emphasis>
                        If your source files have a
                        <filename>configure.ac</filename> file, then your
                        software is built using Autotools.
                        If this is the case, you just need to worry about
                        modifying the configuration.</para>
                        <para>When using Autotools, your recipe needs to inherit
                        the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-autotools'><filename>autotools</filename></ulink>
                        class and your recipe does not have to contain a
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-configure'><filename>do_configure</filename></ulink>
                        task.
                        However, you might still want to make some adjustments.
                        For example, you can set
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OECONF'><filename>EXTRA_OECONF</filename></ulink>
                        to pass any needed configure options that are specific
                        to the recipe.</para></listitem>
                    <listitem><para><emphasis>CMake:</emphasis>
                        If your source files have a
                        <filename>CMakeLists.txt</filename> file, then your
                        software is built using CMake.
                        If this is the case, you just need to worry about
                        modifying the configuration.</para>
                        <para>When you use CMake, your recipe needs to inherit
                        the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-cmake'><filename>cmake</filename></ulink>
                        class and your recipe does not have to contain a
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-configure'><filename>do_configure</filename></ulink>
                        task.
                        You can make some adjustments by setting
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OECMAKE'><filename>EXTRA_OECMAKE</filename></ulink>
                        to pass any needed configure options that are specific
                        to the recipe.</para></listitem>
                    <listitem><para><emphasis>Other:</emphasis>
                        If your source files do not have a
                        <filename>configure.ac</filename> or
                        <filename>CMakeLists.txt</filename> file, then your
                        software is built using some method other than Autotools
                        or CMake.
                        If this is the case, you normally need to provide a
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-configure'><filename>do_configure</filename></ulink>
                        task in your recipe
                        unless, of course, there is nothing to configure.
                        </para>
                        <para>Even if your software is not being built by
                        Autotools or CMake, you still might not need to deal
                        with any configuration issues.
                        You need to determine if configuration is even a required step.
                        You might need to modify a Makefile or some configuration file
                        used for the build to specify necessary build options.
                        Or, perhaps you might need to run a provided, custom
                        configure script with the appropriate options.</para>
                        <para>For the case involving a custom configure
                        script, you would run
                        <filename>./configure --help</filename> and look for
                        the options you need to set.</para></listitem>
                </itemizedlist>
            </para>

            <para>
                Once configuration succeeds, it is always good practice to
                look at the <filename>log.do_configure</filename> file to
                ensure that the appropriate options have been enabled and no
                additional build-time dependencies need to be added to
                <filename>DEPENDS</filename>.
                For example, if the configure script reports that it found
                something not mentioned in <filename>DEPENDS</filename>, or
                that it did not find something that it needed for some
                desired optional functionality, then you would need to add
                those to <filename>DEPENDS</filename>.
                Looking at the log might also reveal items being checked for,
                enabled, or both that you do not want, or items not being found
                that are in <filename>DEPENDS</filename>, in which case
                you would need to look at passing extra options to the
                configure script as needed.
                For reference information on configure options specific to the
                software you are building, you can consult the output of the
                <filename>./configure --help</filename> command within
                <filename>${S}</filename> or consult the software's upstream
                documentation.
            </para>
        </section>

        <section id='new-recipe-compilation'>
            <title>Compilation</title>

            <para>
                During a build, the <filename>do_compile</filename> task
                happens after source is fetched, unpacked, and configured.
                If the recipe passes through <filename>do_compile</filename>
                successfully, nothing needs to be done.
            </para>

            <para>
                However, if the compile step fails, you need to diagnose the
                failure.
                Here are some common issues that cause failures.
                <note>
                    For cases where improper paths are detected for
                    configuration files or for when libraries/headers cannot
                    be found, be sure you are using the more robust
                    <filename>pkg-config</filename>.
                    See the note in section
                    "<link linkend='new-recipe-configuring-the-recipe'>Configuring the Recipe</link>"
                    for additional information.
                </note>
                <itemizedlist>
                    <listitem><para><emphasis>Parallel build failures:</emphasis>
                        These failures manifest themselves as intermittent
                        errors, or errors reporting that a file or directory
                        that should be created by some other part of the build
                        process could not be found.
                        This type of failure can occur even if, upon inspection,
                        the file or directory does exist after the build has
                        failed, because that part of the build process happened
                        in the wrong order.</para>
                        <para>To fix the problem, you need to either satisfy
                        the missing dependency in the Makefile or whatever
                        script produced the Makefile, or (as a workaround)
                        set
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PARALLEL_MAKE'><filename>PARALLEL_MAKE</filename></ulink>
                        to an empty string:
                        <literallayout class='monospaced'>
     PARALLEL_MAKE = ""
                        </literallayout></para>
                        <para>
                            For information on parallel Makefile issues, see the
                            "<link linkend='debugging-parallel-make-races'>Debugging Parallel Make Races</link>"
                            section.
                            </para></listitem>
                    <listitem><para><emphasis>Improper host path usage:</emphasis>
                        This failure applies to recipes building for the target
                        or <filename>nativesdk</filename> only.
                        The failure occurs when the compilation process uses
                        improper headers, libraries, or other files from the
                        host system when cross-compiling for the target.
                        </para>
                        <para>To fix the problem, examine the
                        <filename>log.do_compile</filename> file to identify
                        the host paths being used (e.g.
                        <filename>/usr/include</filename>,
                        <filename>/usr/lib</filename>, and so forth) and then
                        either add configure options, apply a patch, or do both.
                        </para></listitem>
                    <listitem><para><emphasis>Failure to find required
                        libraries/headers:</emphasis>
                        If a build-time dependency is missing because it has
                        not been declared in
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>,
                        or because the dependency exists but the path used by
                        the build process to find the file is incorrect and the
                        configure step did not detect it, the compilation
                        process could fail.
                        For either of these failures, the compilation process
                        notes that files could not be found.
                        In these cases, you need to go back and add additional
                        options to the configure script as well as possibly
                        add additional build-time dependencies to
                        <filename>DEPENDS</filename>.</para>
                        <para>Occasionally, it is necessary to apply a patch
                        to the source to ensure the correct paths are used.
                        If you need to specify paths to find files staged
                        into the sysroot from other recipes, use the variables
                        that the OpenEmbedded build system provides
                        (e.g.
                        <filename>STAGING_BINDIR</filename>,
                        <filename>STAGING_INCDIR</filename>,
                        <filename>STAGING_DATADIR</filename>, and so forth).
<!--
                        (e.g.
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-STAGING_BINDIR'><filename>STAGING_BINDIR</filename></ulink>,
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-STAGING_INCDIR'><filename>STAGING_INCDIR</filename></ulink>,
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-STAGING_DATADIR'><filename>STAGING_DATADIR</filename></ulink>,
                        and so forth).
-->
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='new-recipe-installing'>
            <title>Installing</title>

            <para>
                During <filename>do_install</filename>, the task copies the
                built files along with their hierarchy to locations that
                would mirror their locations on the target device.
                The installation process copies files from the
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink><filename>}</filename>,
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-B'><filename>B</filename></ulink><filename>}</filename>,
                and
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink><filename>}</filename>
                directories to the
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink><filename>}</filename>
                directory to create the structure as it should appear on the
                target system.
            </para>

            <para>
                How your software is built affects what you must do to be
                sure your software is installed correctly.
                The following list describes what you must do for installation
                depending on the type of build system used by the software
                being built:
                <itemizedlist>
                    <listitem><para><emphasis>Autotools and CMake:</emphasis>
                        If the software your recipe is building uses Autotools
                        or CMake, the OpenEmbedded build
                        system understands how to install the software.
                        Consequently, you do not have to have a
                        <filename>do_install</filename> task as part of your
                        recipe.
                        You just need to make sure the install portion of the
                        build completes with no issues.
                        However, if you wish to install additional files not
                        already being installed by
                        <filename>make install</filename>, you should do this
                        using a <filename>do_install_append</filename> function
                        using the install command as described in
                        the "Manual" bulleted item later in this list.
                        </para></listitem>
                    <listitem><para><emphasis>Other (using
                        <filename>make install</filename>):</emphasis>
                        You need to define a
                        <filename>do_install</filename> function in your
                        recipe.
                        The function should call
                        <filename>oe_runmake install</filename> and will likely
                        need to pass in the destination directory as well.
                        How you pass that path is dependent on how the
                        <filename>Makefile</filename> being run is written
                        (e.g. <filename>DESTDIR=${D}</filename>,
                        <filename>PREFIX=${D}</filename>,
                        <filename>INSTALLROOT=${D}</filename>, and so forth).
                        </para>
                        <para>For an example recipe using
                        <filename>make install</filename>, see the
                        "<link linkend='new-recipe-makefile-based-package'>Makefile-Based Package</link>"
                        section.</para></listitem>
                    <listitem><para><emphasis>Manual:</emphasis>
                        You need to define a
                        <filename>do_install</filename> function in your
                        recipe.
                        The function must first use
                        <filename>install -d</filename> to create the
                        directories under
                        <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink><filename>}</filename>.
                        Once the directories exist, your function can use
                        <filename>install</filename> to manually install the
                        built software into the directories.</para>
                        <para>You can find more information on
                        <filename>install</filename> at
                        <ulink url='http://www.gnu.org/software/coreutils/manual/html_node/install-invocation.html'></ulink>.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                For the scenarios that do not use Autotools or
                CMake, you need to track the installation
                and diagnose and fix any issues until everything installs
                correctly.
                You need to look in the default location of
                <filename>${D}</filename>, which is
                <filename>${WORKDIR}/image</filename>, to be sure your
                files have been installed correctly.
            </para>

            <note><title>Notes</title>
                <itemizedlist>
                    <listitem><para>
                        During the installation process, you might need to
                        modify some of the installed files to suit the target
                        layout.
                        For example, you might need to replace hard-coded paths
                        in an initscript with values of variables provided by
                        the build system, such as replacing
                        <filename>/usr/bin/</filename> with
                        <filename>${bindir}</filename>.
                        If you do perform such modifications during
                        <filename>do_install</filename>, be sure to modify the
                        destination file after copying rather than before
                        copying.
                        Modifying after copying ensures that the build system
                        can re-execute <filename>do_install</filename> if
                        needed.
                        </para></listitem>
                    <listitem><para>
                        <filename>oe_runmake install</filename>, which can be
                        run directly or can be run indirectly by the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-autotools'><filename>autotools</filename></ulink>
                        and
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-cmake'><filename>cmake</filename></ulink>
                        classes, runs <filename>make install</filename> in
                        parallel.
                        Sometimes, a Makefile can have missing dependencies
                        between targets that can result in race conditions.
                        If you experience intermittent failures during
                        <filename>do_install</filename>, you might be able to
                        work around them by disabling parallel Makefile
                        installs by adding the following to the recipe:
                        <literallayout class='monospaced'>
     PARALLEL_MAKEINST = ""
                        </literallayout>
                        See
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PARALLEL_MAKEINST'><filename>PARALLEL_MAKEINST</filename></ulink>
                        for additional information.
                        </para></listitem>
                </itemizedlist>
            </note>
        </section>

        <section id='new-recipe-enabling-system-services'>
            <title>Enabling System Services</title>

            <para>
                If you want to install a service, which is a process that
                usually starts on boot and runs in the background, then
                you must include some additional definitions in your recipe.
            </para>

            <para>
                If you are adding services and the service initialization
                script or the service file itself is not installed, you must
                provide for that installation in your recipe using a
                <filename>do_install_append</filename> function.
                If your recipe already has a <filename>do_install</filename>
                function, update the function near its end rather than
                adding an additional <filename>do_install_append</filename>
                function.
            </para>

            <para>
                When you create the installation for your services, you need
                to accomplish what is normally done by
                <filename>make install</filename>.
                In other words, make sure your installation arranges the output
                similar to how it is arranged on the target system.
            </para>

            <para>
                The OpenEmbedded build system provides support for starting
                services two different ways:
                <itemizedlist>
                    <listitem><para><emphasis>SysVinit:</emphasis>
                        SysVinit is a system and service manager that
                        manages the init system used to control the very basic
                        functions of your system.
                        The init program is the first program
                        started by the Linux kernel when the system boots.
                        Init then controls the startup, running and shutdown
                        of all other programs.</para>
                        <para>To enable a service using SysVinit, your recipe
                        needs to inherit the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-update-rc.d'><filename>update-rc.d</filename></ulink>
                        class.
                        The class helps facilitate safely installing the
                        package on the target.</para>
                        <para>You will need to set the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-INITSCRIPT_PACKAGES'><filename>INITSCRIPT_PACKAGES</filename></ulink>,
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-INITSCRIPT_NAME'><filename>INITSCRIPT_NAME</filename></ulink>,
                        and
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-INITSCRIPT_PARAMS'><filename>INITSCRIPT_PARAMS</filename></ulink>
                        variables within your recipe.</para></listitem>
                    <listitem><para><emphasis>systemd:</emphasis>
                        System Management Daemon (systemd) was designed to
                        replace SysVinit and to provide
                        enhanced management of services.
                        For more information on systemd, see the systemd
                        homepage at
                        <ulink url='http://freedesktop.org/wiki/Software/systemd/'></ulink>.
                        </para>
                        <para>To enable a service using systemd, your recipe
                        needs to inherit the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-systemd'><filename>systemd</filename></ulink>
                        class.
                        See the <filename>systemd.bbclass</filename> file
                        located in your
                        <link linkend='source-directory'>Source Directory</link>.
                        section for more information.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='new-recipe-packaging'>
            <title>Packaging</title>

            <para>
                Successful packaging is a combination of automated processes
                performed by the OpenEmbedded build system and some
                specific steps you need to take.
                The following list describes the process:
                <itemizedlist>
                    <listitem><para><emphasis>Splitting Files</emphasis>:
                        The <filename>do_package</filename> task splits the
                        files produced by the recipe into logical components.
                        Even software that produces a single binary might
                        still have debug symbols, documentation, and other
                        logical components that should be split out.
                        The <filename>do_package</filename> task ensures
                        that files are split up and packaged correctly.
                        </para></listitem>
                    <listitem><para><emphasis>Running QA Checks</emphasis>:
                        The
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-insane'><filename>insane</filename></ulink>
                        class adds a step to
                        the package generation process so that output quality
                        assurance checks are generated by the OpenEmbedded
                        build system.
                        This step performs a range of checks to be sure the
                        build's output is free of common problems that show
                        up during runtime.
                        For information on these checks, see the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-insane'><filename>insane</filename></ulink>
                        class and the
                        "<ulink url='&YOCTO_DOCS_REF_URL;#ref-qa-checks'>QA Error and Warning Messages</ulink>"
                        chapter in the Yocto Project Reference Manual.
                        </para></listitem>
                    <listitem><para><emphasis>Hand-Checking Your Packages</emphasis>:
                        After you build your software, you need to be sure
                        your packages are correct.
                        Examine the
                        <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink><filename>}/packages-split</filename>
                        directory and make sure files are where you expect
                        them to be.
                        If you discover problems, you can set
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>,
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES</filename></ulink>,
                        <filename>do_install(_append)</filename>, and so forth as
                        needed.
                        </para></listitem>
                    <listitem><para><emphasis>Splitting an Application into Multiple Packages</emphasis>:
                        If you need to split an application into several
                        packages, see the
                        "<link linkend='splitting-an-application-into-multiple-packages'>Splitting an Application into Multiple Packages</link>"
                        section for an example.
                        </para></listitem>
                    <listitem><para><emphasis>Installing a Post-Installation Script</emphasis>:
                        For an example showing how to install a
                        post-installation script, see the
                        "<link linkend='new-recipe-post-installation-scripts'>Post-Installation Scripts</link>"
                        section.
                        </para></listitem>
                    <listitem><para><emphasis>Marking Package Architecture</emphasis>:
                        Depending on what your recipe is building and how it
                        is configured, it might be important to mark the
                        packages produced as being specific to a particular
                        machine, or to mark them as not being specific to
                        a particular machine or architecture at all.</para>
                        <para>By default, packages apply to any machine with the
                        same architecture as the target machine.
                        When a recipe produces packages that are
                        machine-specific (e.g. the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
                        value is passed into the configure script or a patch
                        is applied only for a particular machine), you should
                        mark them as such by adding the following to the
                        recipe:
                        <literallayout class='monospaced'>
     PACKAGE_ARCH = "${MACHINE_ARCH}"
                        </literallayout></para>
                        <para>On the other hand, if the recipe produces packages
                        that do not contain anything specific to the target
                        machine or architecture at all (e.g. recipes
                        that simply package script files or configuration
                        files), you should use the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-allarch'><filename>allarch</filename></ulink>
                        class to do this for you by adding this to your
                        recipe:
                        <literallayout class='monospaced'>
     inherit allarch
                        </literallayout>
                        Ensuring that the package architecture is correct is
                        not critical while you are doing the first few builds
                        of your recipe.
                        However, it is important in order
                        to ensure that your recipe rebuilds (or does not
                        rebuild) appropriately in response to changes in
                        configuration, and to ensure that you get the
                        appropriate packages installed on the target machine,
                        particularly if you run separate builds for more
                        than one target machine.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='properly-versioning-pre-release-recipes'>
            <title>Properly Versioning Pre-Release Recipes</title>

            <para>
                Sometimes the name of a recipe can lead to versioning
                problems when the recipe is upgraded to a final release.
                For example, consider the
                <filename>irssi_0.8.16-rc1.bb</filename> recipe file in
                the list of example recipes in the
                "<link linkend='new-recipe-storing-and-naming-the-recipe'>Storing and Naming the Recipe</link>"
                section.
                This recipe is at a release candidate stage (i.e.
                "rc1").
                When the recipe is released, the recipe filename becomes
                <filename>irssi_0.8.16.bb</filename>.
                The version change from <filename>0.8.16-rc1</filename>
                to <filename>0.8.16</filename> is seen as a decrease by the
                build system and package managers, so the resulting packages
                will not correctly trigger an upgrade.
            </para>

            <para>
                In order to ensure the versions compare properly, the
                recommended convention is to set
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
                within the recipe to
                "<replaceable>previous_version</replaceable>+<replaceable>current_version</replaceable>".
                You can use an additional variable so that you can use the
                current version elsewhere.
                Here is an example:
                <literallayout class='monospaced'>
     REALPV = "0.8.16-rc1"
     PV = "0.8.15+${REALPV}"
                </literallayout>
            </para>
        </section>

        <section id='new-recipe-post-installation-scripts'>
            <title>Post-Installation Scripts</title>

            <para>
                Post-installation scripts run immediately after installing
                a package on the target or during image creation when a
                package is included in an image.
                To add a post-installation script to a package, add a
                <filename>pkg_postinst_PACKAGENAME()</filename> function to
                the recipe file (<filename>.bb</filename>) and replace
                <filename>PACKAGENAME</filename> with the name of the package
                you want to attach to the <filename>postinst</filename>
                script.
                To apply the post-installation script to the main package
                for the recipe, which is usually what is required, specify
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink><filename>}</filename>
                in place of <filename>PACKAGENAME</filename>.
            </para>

            <para>
                A post-installation function has the following structure:
                <literallayout class='monospaced'>
     pkg_postinst_PACKAGENAME() {
     # Commands to carry out
     }
                </literallayout>
            </para>

            <para>
                The script defined in the post-installation function is
                called when the root filesystem is created.
                If the script succeeds, the package is marked as installed.
                If the script fails, the package is marked as unpacked and
                the script is executed when the image boots again.
            </para>

            <para>
                Sometimes it is necessary for the execution of a
                post-installation script to be delayed until the first boot.
                For example, the script might need to be executed on the
                device itself.
                To delay script execution until boot time, use the following
                structure in the post-installation script:
                <literallayout class='monospaced'>
     pkg_postinst_PACKAGENAME() {
     if [ x"$D" = "x" ]; then
          # Actions to carry out on the device go here
     else
          exit 1
     fi
     }
                </literallayout>
            </para>

            <para>
                The previous example delays execution until the image boots
                again because the environment variable <filename>D</filename>
                points to the directory containing the image when
                the root filesystem is created at build time but is unset
                when executed on the first boot.
            </para>

            <note>
                Equivalent support for pre-install, pre-uninstall, and
                post-uninstall scripts exist by way of
                <filename>pkg_preinst</filename>,
                <filename>pkg_prerm</filename>, and
                <filename>pkg_postrm</filename>, respectively.
                These scrips work in exactly the same way as does
                <filename>pkg_postinst</filename> with the exception that they
                run at different times.
                Also, because of when they run, they are not applicable to
                being run at image creation time like
                <filename>pkg_postinst</filename>.
            </note>
        </section>

        <section id='new-recipe-testing'>
            <title>Testing</title>

            <para>
                The final step for completing your recipe is to be sure that
                the software you built runs correctly.
                To accomplish runtime testing, add the build's output
                packages to your image and test them on the target.
            </para>

            <para>
                For information on how to customize your image by adding
                specific packages, see the
                "<link linkend='usingpoky-extend-customimage'>Customizing Images</link>"
                section.
            </para>
        </section>

        <section id='new-recipe-testing-examples'>
            <title>Examples</title>

            <para>
                To help summarize how to write a recipe, this section provides
                some examples given various scenarios:
                <itemizedlist>
                    <listitem><para>Recipes that use local files</para></listitem>
                    <listitem><para>Using an Autotooled package</para></listitem>
                    <listitem><para>Using a Makefile-based package</para></listitem>
                    <listitem><para>Splitting an application into multiple packages</para></listitem>
                    <listitem><para>Adding binaries to an image</para></listitem>
                </itemizedlist>
            </para>

            <section id='new-recipe-single-c-file-package-hello-world'>
                <title>Single .c File Package (Hello World!)</title>

                <para>
                    Building an application from a single file that is stored
                    locally (e.g. under <filename>files</filename>) requires
                    a recipe that has the file listed in the
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>
                    variable.
                    Additionally, you need to manually write the
                    <filename>do_compile</filename> and
                    <filename>do_install</filename> tasks.
                    The <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'>S</ulink></filename>
                    variable defines the directory containing the source code,
                    which is set to
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>
                    in this case - the directory BitBake uses for the build.
                    <literallayout class='monospaced'>
     SUMMARY = "Simple helloworld application"
     SECTION = "examples"
     LICENSE = "MIT"
     LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/MIT;md5=0835ade698e0bcf8506ecda2f7b4f302"

     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}
     }
                    </literallayout>
                </para>

                <para>
                    By default, the <filename>helloworld</filename>,
                    <filename>helloworld-dbg</filename>, and
                    <filename>helloworld-dev</filename> packages are built.
                    For information on how to customize the packaging process,
                    see the
                    "<link linkend='splitting-an-application-into-multiple-packages'>Splitting an Application into Multiple Packages</link>"
                    section.
                </para>
            </section>

            <section id='new-recipe-autotooled-package'>
                <title>Autotooled Package</title>
                <para>
                    Applications that use Autotools such as <filename>autoconf</filename> and
                    <filename>automake</filename> require a recipe that has a source archive listed in
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename> and
                    also inherit the
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-autotools'><filename>autotools</filename></ulink>
                    class, 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: (<filename>hello_2.3.bb</filename>)
                    <literallayout class='monospaced'>
     SUMMARY = "GNU Helloworld application"
     SECTION = "examples"
     LICENSE = "GPLv2+"
     LIC_FILES_CHKSUM = "file://COPYING;md5=751419260aa954499f7abaabaa882bbe"

     SRC_URI = "${GNU_MIRROR}/hello/hello-${PV}.tar.gz"

     inherit autotools gettext
                     </literallayout>
                </para>

                <para>
                    The variable
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LIC_FILES_CHKSUM'>LIC_FILES_CHKSUM</ulink></filename>
                    is used to track source license changes as described in the
                    "<ulink url='&YOCTO_DOCS_REF_URL;#usingpoky-configuring-LIC_FILES_CHKSUM'>Tracking License Changes</ulink>" section.
                    You can quickly create Autotool-based recipes in a manner similar to the previous example.
                </para>
            </section>

            <section id='new-recipe-makefile-based-package'>
                <title>Makefile-Based Package</title>

                <para>
                    Applications that use GNU <filename>make</filename> also require a recipe that has
                    the source archive listed in
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>.
                    You do not need to add a <filename>do_compile</filename> step since by default BitBake
                    starts the <filename>make</filename> command to compile the application.
                    If you need additional <filename>make</filename> options, you should store them in the
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OEMAKE'>EXTRA_OEMAKE</ulink></filename>
                    variable.
                    BitBake passes these options into the GNU <filename>make</filename> invocation.
                    Note that a <filename>do_install</filename> task is still required.
                    Otherwise, BitBake runs an empty <filename>do_install</filename> task by default.
                </para>

               <para>
                    Some applications might require extra parameters to be passed to the compiler.
                    For example, the application might need an additional header path.
                    You can accomplish this by adding to the
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-CFLAGS'>CFLAGS</ulink></filename> variable.
                    The following example shows this:
                    <literallayout class='monospaced'>
     CFLAGS_prepend = "-I ${S}/include "
                    </literallayout>
                </para>

                <para>
                In the following example, <filename>mtd-utils</filename> is a makefile-based package:
                    <literallayout class='monospaced'>
     SUMMARY = "Tools for managing memory technology devices"
     SECTION = "base"
     DEPENDS = "zlib lzo e2fsprogs util-linux"
     HOMEPAGE = "http://www.linux-mtd.infradead.org/"
     LICENSE = "GPLv2+"
     LIC_FILES_CHKSUM = "file://COPYING;md5=0636e73ff0215e8d672dc4c32c317bb3 \
                         file://include/common.h;beginline=1;endline=17;md5=ba05b07912a44ea2bf81ce409380049c"

     # Use the latest version at 26 Oct, 2013
     SRCREV = "9f107132a6a073cce37434ca9cda6917dd8d866b"
     SRC_URI = "git://git.infradead.org/mtd-utils.git \
                     file://add-exclusion-to-mkfs-jffs2-git-2.patch \
     "

     PV = "1.5.1+git${SRCPV}"

     S = "${WORKDIR}/git"

     EXTRA_OEMAKE = "'CC=${CC}' 'RANLIB=${RANLIB}' 'AR=${AR}' 'CFLAGS=${CFLAGS} -I${S}/include -DWITHOUT_XATTR' 'BUILDDIR=${S}'"

     do_install () {
             oe_runmake install DESTDIR=${D} SBINDIR=${sbindir} MANDIR=${mandir} INCLUDEDIR=${includedir}
     }

     PACKAGES =+ "mtd-utils-jffs2 mtd-utils-ubifs mtd-utils-misc"

     FILES_mtd-utils-jffs2 = "${sbindir}/mkfs.jffs2 ${sbindir}/jffs2dump ${sbindir}/jffs2reader ${sbindir}/sumtool"
     FILES_mtd-utils-ubifs = "${sbindir}/mkfs.ubifs ${sbindir}/ubi*"
     FILES_mtd-utils-misc = "${sbindir}/nftl* ${sbindir}/ftl* ${sbindir}/rfd* ${sbindir}/doc* ${sbindir}/serve_image ${sbindir}/recv_image"

     PARALLEL_MAKE = ""

     BBCLASSEXTEND = "native"
                    </literallayout>
                </para>
            </section>

            <section id='splitting-an-application-into-multiple-packages'>
                <title>Splitting an Application into Multiple Packages</title>

                <para>
                    You can use the variables
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'>PACKAGES</ulink></filename> and
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'>FILES</ulink></filename>
                    to split an application into multiple packages.
                </para>

                <para>
                    Following is an example that uses the <filename>libxpm</filename> recipe.
                    By default, this recipe generates a single package that contains the library along
                    with a few binaries.
                    You can modify the recipe to split the binaries into separate packages:
                    <literallayout class='monospaced'>
     require xorg-lib-common.inc

     SUMMARY = "Xpm: X Pixmap extension library"
     LICENSE = "BSD"
     LIC_FILES_CHKSUM = "file://COPYING;md5=51f4270b012ecd4ab1a164f5f4ed6cf7"
     DEPENDS += "libxext libsm libxt"
     PE = "1"

     XORG_PN = "libXpm"

     PACKAGES =+ "sxpm cxpm"
     FILES_cxpm = "${bindir}/cxpm"
     FILES_sxpm = "${bindir}/sxpm"
                    </literallayout>
                </para>

                <para>
                    In the previous example, we want to ship the <filename>sxpm</filename>
                    and <filename>cxpm</filename> binaries in separate packages.
                    Since <filename>bindir</filename> would be packaged into the main
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'>PN</ulink></filename>
                    package by default, we prepend the <filename>PACKAGES</filename>
                    variable so additional package names are added to the start of list.
                    This results in the extra <filename>FILES_*</filename>
                    variables then containing information that define which files and
                    directories go into which packages.
                    Files included by earlier packages are skipped by latter packages.
                    Thus, the main <filename>PN</filename> package
                    does not include the above listed files.
                </para>
            </section>

            <section id='packaging-externally-produced-binaries'>
                <title>Packaging Externally Produced Binaries</title>

                <para>
                    Sometimes, you need to add pre-compiled binaries to an
                    image.
                    For example, suppose that binaries for proprietary code
                    exist, which are created by a particular division of a
                    company.
                    Your part of the company needs to use those binaries as
                    part of an image that you are building using the
                    OpenEmbedded build system.
                    Since you only have the binaries and not the source code,
                    you cannot use a typical recipe that expects to fetch the
                    source specified in
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                    and then compile it.
                </para>

                <para>
                    One method is to package the binaries and then install them
                    as part of the image.
                    Generally, it is not a good idea to package binaries
                    since, among other things, it can hinder the ability to
                    reproduce builds and could lead to compatibility problems
                    with ABI in the future.
                    However, sometimes you have no choice.
                </para>

                <para>
                    The easiest solution is to create a recipe that uses
                    the
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-bin-package'><filename>bin_package</filename></ulink>
                    class and to be sure that you are using default locations
                    for build artifacts.
                    In most cases, the <filename>bin_package</filename> class
                    handles "skipping" the configure and compile steps as well
                    as sets things up to grab packages from the appropriate
                    area.
                    In particular, this class sets <filename>noexec</filename>
                    on both the
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-configure'><filename>do_configure</filename></ulink>
                    and
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-compile'><filename>do_compile</filename></ulink>
                    tasks, sets
                    <filename>FILES_${PN}</filename> to "/" so that it picks
                    up all files, and sets up a
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink>
                    task, which effectively copies all files from
                    <filename>${S}</filename> to <filename>${D}</filename>.
                    The <filename>bin_package</filename> class works well when
                    the files extracted into <filename>${S}</filename> are
                    already laid out in the way they should be laid out
                    on the target.
                    For more information on these variables, see the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink>,
                    and
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink>
                    variables in the Yocto Project Reference Manual's variable
                    glossary.
                </para>

                <para>
                    If you can't use the <filename>bin_package</filename>
                    class, you need to be sure you are doing the following:
                    <itemizedlist>
                        <listitem><para>Create a recipe where the
                            <filename>do_configure</filename> and
                            <filename>do_compile</filename> tasks do nothing:
                            <literallayout class='monospaced'>
     do_configure[noexec] = "1"
     do_compile[noexec] = "1"
                            </literallayout>
                            Alternatively, you can make these tasks an empty
                            function.
                            </para></listitem>
                        <listitem><para>Make sure your
                            <filename>do_install</filename> task installs the
                            binaries appropriately.
                            </para></listitem>
                        <listitem><para>Ensure that you set up
                            <filename>FILES</filename> (usually
                            <filename>FILES_${PN}</filename>) to point to the
                            files you have installed, which of course depends
                            on where you have installed them and whether
                            those files are in different locations than the
                            defaults.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>
        </section>
    </section>

    <section id="platdev-newmachine">
        <title>Adding a New Machine</title>

        <para>
            Adding a new machine to the Yocto Project is a straightforward
            process.
            This section describes how to add machines that are similar
            to those that the Yocto Project already supports.
            <note>
                Although well within the capabilities of the Yocto Project,
                adding a totally new architecture might require
                changes to <filename>gcc/glibc</filename> and to the site
                information, which is beyond the scope of this manual.
            </note>
        </para>

        <para>
            For a complete example that shows how to add a new machine,
            see the
            "<ulink url='&YOCTO_DOCS_BSP_URL;#creating-a-new-bsp-layer-using-the-yocto-bsp-script'>Creating a New BSP Layer Using the yocto-bsp Script</ulink>"
            section in the Yocto Project Board Support Package (BSP) Developer's Guide.
        </para>

        <section id="platdev-newmachine-conffile">
            <title>Adding the Machine Configuration File</title>

            <para>
                To add a new machine, you need to add a new machine
                configuration file to the layer's
                <filename>conf/machine</filename> directory.
                This configuration file provides details about the device
                you are adding.
            </para>

            <para>
                The OpenEmbedded build system uses the root name of the
                machine configuration file to reference the new machine.
                For example, given a machine configuration file named
                <filename>crownbay.conf</filename>, the build system
                recognizes the machine as "crownbay".
            </para>

            <para>
                The most important variables you must set in your machine
                configuration file or include from a lower-level configuration
                file are as follows:
                <itemizedlist>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-TARGET_ARCH'>TARGET_ARCH</ulink></filename>
                        (e.g. "arm")</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PREFERRED_PROVIDER'>PREFERRED_PROVIDER</ulink>_virtual/kernel</filename>
                        </para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_FEATURES'>MACHINE_FEATURES</ulink></filename>
                        (e.g. "apm screen wifi")</para></listitem>
                </itemizedlist>
            </para>

            <para>
                You might also need these variables:
                <itemizedlist>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SERIAL_CONSOLES'>SERIAL_CONSOLES</ulink></filename>
                        (e.g. "115200;ttyS0 115200;ttyS1")</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_IMAGETYPE'>KERNEL_IMAGETYPE</ulink></filename>
                        (e.g. "zImage")</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FSTYPES'>IMAGE_FSTYPES</ulink></filename>
                        (e.g. "tar.gz jffs2")</para></listitem>
                </itemizedlist>
            </para>

            <para>
                You can find full details on these variables in the reference
                section.
                You can leverage existing machine <filename>.conf</filename>
                files from <filename>meta-yocto-bsp/conf/machine/</filename>.
            </para>
        </section>

        <section id="platdev-newmachine-kernel">
            <title>Adding a Kernel for the Machine</title>

            <para>
                The OpenEmbedded build system needs to be able to build a kernel
                for the machine.
                You need to either create a new kernel recipe for this machine,
                or extend an existing kernel recipe.
                You can find several kernel recipe examples in the
                Source Directory at
                <filename>meta/recipes-kernel/linux</filename>
                that you can use as references.
            </para>

            <para>
                If you are creating a new kernel recipe, normal recipe-writing
                rules apply for setting up a
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>.
                Thus, you need to specify any necessary patches and set
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'>S</ulink></filename>
                to point at the source code.
                You need to create a <filename>do_configure</filename> task that
                configures the unpacked kernel with a
                <filename>defconfig</filename> file.
                You can do this by using a <filename>make defconfig</filename>
                command or, more commonly, by copying in a suitable
                <filename>defconfig</filename> file and then running
                <filename>make oldconfig</filename>.
                By making use of <filename>inherit kernel</filename> and
                potentially some of the <filename>linux-*.inc</filename> files,
                most other functionality is centralized and the defaults of the
                class normally work well.
            </para>

            <para>
                If you are extending an existing kernel recipe, it is usually
                a matter of adding a suitable <filename>defconfig</filename>
                file.
                The file needs to be added into a location similar to
                <filename>defconfig</filename> files used for other machines
                in a given kernel recipe.
                A possible way to do this is by listing the file in the
                <filename>SRC_URI</filename> and adding the machine to the
                expression in
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-COMPATIBLE_MACHINE'>COMPATIBLE_MACHINE</ulink></filename>:
                <literallayout class='monospaced'>
     COMPATIBLE_MACHINE = '(qemux86|qemumips)'
                </literallayout>
                For more information on <filename>defconfig</filename> files,
                see the
                "<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#changing-the-configuration'>Changing the Configuration</ulink>"
                section in the Yocto Project Linux Kernel Development Manual.
            </para>
        </section>

        <section id="platdev-newmachine-formfactor">
            <title>Adding a Formfactor Configuration File</title>

            <para>
                A formfactor configuration file provides information about the
                target hardware for which the image is being built and information that
                the build system cannot obtain from other sources such as the kernel.
                Some examples of information contained in a formfactor configuration file include
                framebuffer orientation, whether or not the system has a keyboard,
                the positioning of the keyboard in relation to the screen, and
                the screen resolution.
            </para>

            <para>
                The build system uses reasonable defaults in most cases.
                However, if customization is
                necessary, you need to create a <filename>machconfig</filename> file
                in the <filename>meta/recipes-bsp/formfactor/files</filename>
                directory.
                This directory contains directories for specific machines such as
                <filename>qemuarm</filename> and <filename>qemux86</filename>.
                For information about the settings available and the defaults, see the
                <filename>meta/recipes-bsp/formfactor/files/config</filename> file found in the
                same area.
            </para>

            <para>
                Following is an example for "qemuarm" machine:
                <literallayout class='monospaced'>
     HAVE_TOUCHSCREEN=1
     HAVE_KEYBOARD=1

     DISPLAY_CAN_ROTATE=0
     DISPLAY_ORIENTATION=0
     #DISPLAY_WIDTH_PIXELS=640
     #DISPLAY_HEIGHT_PIXELS=480
     #DISPLAY_BPP=16
     DISPLAY_DPI=150
     DISPLAY_SUBPIXEL_ORDER=vrgb
                </literallayout>
            </para>
        </section>
    </section>

    <section id="platdev-working-with-libraries">
        <title>Working With Libraries</title>

        <para>
            Libraries are an integral part of your system.
            This section describes some common practices you might find
            helpful when working with libraries to build your system:
            <itemizedlist>
                <listitem><para><link linkend='including-static-library-files'>How to include static library files</link>
                    </para></listitem>
                <listitem><para><link linkend='combining-multiple-versions-library-files-into-one-image'>How to use the Multilib feature to combine multiple versions of library files into a single image</link>
                    </para></listitem>
                <listitem><para><link linkend='installing-multiple-versions-of-the-same-library'>How to install multiple versions of the same library in parallel on the same system</link>
                    </para></listitem>
            </itemizedlist>
        </para>

        <section id='including-static-library-files'>
            <title>Including Static Library Files</title>

            <para>
                If you are building a library and the library offers static linking, you can control
                which static library files (<filename>*.a</filename> files) get included in the
                built library.
            </para>

            <para>
                The <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>
                and <ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES_*</filename></ulink>
                variables in the
                <filename>meta/conf/bitbake.conf</filename> configuration file define how files installed
                by the <filename>do_install</filename> task are packaged.
                By default, the <filename>PACKAGES</filename> variable includes
                <filename>${PN}-staticdev</filename>, which represents all static library files.
                <note>
                    Some previously released versions of the Yocto Project
                    defined the static library files through
                    <filename>${PN}-dev</filename>.
                </note>
                Following is part of the BitBake configuration file, where
                you can see how the static library files are defined:
                <literallayout class='monospaced'>
     PACKAGE_BEFORE_PN ?= ""
     PACKAGES = "${PN}-dbg ${PN}-staticdev ${PN}-dev ${PN}-doc ${PN}-locale ${PACKAGE_BEFORE_PN} ${PN}"
     PACKAGES_DYNAMIC = "^${PN}-locale-.*"
     FILES = ""

     FILES_${PN} = "${bindir}/* ${sbindir}/* ${libexecdir}/* ${libdir}/lib*${SOLIBS} \
                 ${sysconfdir} ${sharedstatedir} ${localstatedir} \
                 ${base_bindir}/* ${base_sbindir}/* \
                 ${base_libdir}/*${SOLIBS} \
                 ${base_prefix}/lib/udev/rules.d ${prefix}/lib/udev/rules.d \
                 ${datadir}/${BPN} ${libdir}/${BPN}/* \
                 ${datadir}/pixmaps ${datadir}/applications \
                 ${datadir}/idl ${datadir}/omf ${datadir}/sounds \
                 ${libdir}/bonobo/servers"

     FILES_${PN}-bin = "${bindir}/* ${sbindir}/*"

     FILES_${PN}-doc = "${docdir} ${mandir} ${infodir} ${datadir}/gtk-doc \
                 ${datadir}/gnome/help"
     SECTION_${PN}-doc = "doc"

     FILES_SOLIBSDEV ?= "${base_libdir}/lib*${SOLIBSDEV} ${libdir}/lib*${SOLIBSDEV}"
     FILES_${PN}-dev = "${includedir} ${FILES_SOLIBSDEV} ${libdir}/*.la \
                     ${libdir}/*.o ${libdir}/pkgconfig ${datadir}/pkgconfig \
                     ${datadir}/aclocal ${base_libdir}/*.o \
                     ${libdir}/${BPN}/*.la ${base_libdir}/*.la"
     SECTION_${PN}-dev = "devel"
     ALLOW_EMPTY_${PN}-dev = "1"
     RDEPENDS_${PN}-dev = "${PN} (= ${EXTENDPKGV})"

     FILES_${PN}-staticdev = "${libdir}/*.a ${base_libdir}/*.a ${libdir}/${BPN}/*.a"
     SECTION_${PN}-staticdev = "devel"
     RDEPENDS_${PN}-staticdev = "${PN}-dev (= ${EXTENDPKGV})"
                </literallayout>
            </para>
        </section>

        <section id="combining-multiple-versions-library-files-into-one-image">
            <title>Combining Multiple Versions of Library Files into One Image</title>

            <para>
                The build system offers the ability to build libraries with different
                target optimizations or architecture formats and combine these together
                into one system image.
                You can link different binaries in the image
                against the different libraries as needed for specific use cases.
                This feature is called "Multilib."
            </para>

            <para>
                An example would be where you have most of a system compiled in 32-bit
                mode using 32-bit libraries, but you have something large, like a database
                engine, that needs to be a 64-bit application and uses 64-bit libraries.
                Multilib allows you to get the best of both 32-bit and 64-bit libraries.
            </para>

            <para>
                While the Multilib feature is most commonly used for 32 and 64-bit differences,
                the approach the build system uses facilitates different target optimizations.
                You could compile some binaries to use one set of libraries and other binaries
                to use a different set of libraries.
                The libraries could differ in architecture, compiler options, or other
                optimizations.
            </para>

            <para>
                Several examples exist in the
                <filename>meta-skeleton</filename> layer found in the
               <link linkend='source-directory'>Source Directory</link>:
                <itemizedlist>
                    <listitem><para><filename>conf/multilib-example.conf</filename>
                        configuration file</para></listitem>
                    <listitem><para><filename>conf/multilib-example2.conf</filename>
                        configuration file</para></listitem>
                    <listitem><para><filename>recipes-multilib/images/core-image-multilib-example.bb</filename>
                        recipe</para></listitem>
                </itemizedlist>
            </para>

            <section id='preparing-to-use-multilib'>
                <title>Preparing to Use Multilib</title>

                <para>
                    User-specific requirements drive the Multilib feature.
                    Consequently, there is no one "out-of-the-box" configuration that likely
                    exists to meet your needs.
                </para>

                <para>
                    In order to enable Multilib, you first need to ensure your recipe is
                    extended to support multiple libraries.
                    Many standard recipes are already extended and support multiple libraries.
                    You can check in the <filename>meta/conf/multilib.conf</filename>
                    configuration file in the
                    <link linkend='source-directory'>Source Directory</link> to see how this is
                    done using the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-BBCLASSEXTEND'><filename>BBCLASSEXTEND</filename></ulink>
                    variable.
                    Eventually, all recipes will be covered and this list will
                    not be needed.
                </para>

                <para>
                    For the most part, the Multilib class extension works automatically to
                    extend the package name from <filename>${PN}</filename> to
                    <filename>${MLPREFIX}${PN}</filename>, where <filename>MLPREFIX</filename>
                    is the particular multilib (e.g. "lib32-" or "lib64-").
                    Standard variables such as
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-RPROVIDES'><filename>RPROVIDES</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'><filename>RRECOMMENDS</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>, and
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES_DYNAMIC'><filename>PACKAGES_DYNAMIC</filename></ulink>
                    are automatically extended by the system.
                    If you are extending any manual code in the recipe, you can use the
                    <filename>${MLPREFIX}</filename> variable to ensure those names are extended
                    correctly.
                    This automatic extension code resides in <filename>multilib.bbclass</filename>.
                </para>
            </section>

            <section id='using-multilib'>
                <title>Using Multilib</title>

                <para>
                    After you have set up the recipes, you need to define the actual
                    combination of multiple libraries you want to build.
                    You accomplish this through your <filename>local.conf</filename>
                    configuration file in the
                    <link linkend='build-directory'>Build Directory</link>.
                    An example configuration would be as follows:
                    <literallayout class='monospaced'>
     MACHINE = "qemux86-64"
     require conf/multilib.conf
     MULTILIBS = "multilib:lib32"
     DEFAULTTUNE_virtclass-multilib-lib32 = "x86"
     IMAGE_INSTALL_append = " lib32-glib-2.0"
                    </literallayout>
                    This example enables an
                    additional library named <filename>lib32</filename> alongside the
                    normal target packages.
                    When combining these "lib32" alternatives, the example uses "x86" for tuning.
                    For information on this particular tuning, see
                    <filename>meta/conf/machine/include/ia32/arch-ia32.inc</filename>.
                </para>

                <para>
                    The example then includes <filename>lib32-glib-2.0</filename>
                    in all the images, which illustrates one method of including a
                    multiple library dependency.
                    You can use a normal image build to include this dependency,
                    for example:
                    <literallayout class='monospaced'>
     $ bitbake core-image-sato
                    </literallayout>
                    You can also build Multilib packages specifically with a command like this:
                    <literallayout class='monospaced'>
     $ bitbake lib32-glib-2.0
                    </literallayout>
                </para>
            </section>

            <section id='additional-implementation-details'>
                <title>Additional Implementation Details</title>

                <para>
                    Generic implementation details as well as details that are
                    specific to package management systems exist.
                    Following are implementation details that exist regardless
                    of the package management system:
                    <itemizedlist>
                        <listitem><para>The typical convention used for the
                            class extension code as used by
                            Multilib assumes that all package names specified
                            in
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>
                            that contain <filename>${PN}</filename> have
                            <filename>${PN}</filename> at the start of the name.
                            When that convention is not followed and
                            <filename>${PN}</filename> appears at
                            the middle or the end of a name, problems occur.
                            </para></listitem>
                        <listitem><para>The
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-TARGET_VENDOR'><filename>TARGET_VENDOR</filename></ulink>
                            value under Multilib will be extended to
                            "-<replaceable>vendor</replaceable>ml<replaceable>multilib</replaceable>"
                            (e.g. "-pokymllib32" for a "lib32" Multilib with
                            Poky).
                            The reason for this slightly unwieldy contraction
                            is that any "-" characters in the vendor
                            string presently break Autoconf's
                            <filename>config.sub</filename>, and
                            other separators are problematic for different
                            reasons.
                            </para></listitem>
                    </itemizedlist>
                </para>
'
                <para>
                    For the RPM Package Management System, the following implementation details
                    exist:
                    <itemizedlist>
                        <listitem><para>A unique architecture is defined for the Multilib packages,
                            along with creating a unique deploy folder under
                            <filename>tmp/deploy/rpm</filename> in the
                            <link linkend='build-directory'>Build Directory</link>.
                            For example, consider <filename>lib32</filename> in a
                            <filename>qemux86-64</filename> image.
                            The possible architectures in the system are "all", "qemux86_64",
                            "lib32_qemux86_64", and "lib32_x86".</para></listitem>
                        <listitem><para>The <filename>${MLPREFIX}</filename> variable is stripped from
                            <filename>${PN}</filename> during RPM packaging.
                            The naming for a normal RPM package and a Multilib RPM package in a
                            <filename>qemux86-64</filename> system resolves to something similar to
                            <filename>bash-4.1-r2.x86_64.rpm</filename> and
                            <filename>bash-4.1.r2.lib32_x86.rpm</filename>, respectively.
                            </para></listitem>
                        <listitem><para>When installing a Multilib image, the RPM backend first
                            installs the base image and then installs the Multilib libraries.
                            </para></listitem>
                        <listitem><para>The build system relies on RPM to resolve the identical files in the
                            two (or more) Multilib packages.</para></listitem>
                    </itemizedlist>
                </para>

                <para>
                    For the IPK Package Management System, the following implementation details exist:
                    <itemizedlist>
                        <listitem><para>The <filename>${MLPREFIX}</filename> is not stripped from
                            <filename>${PN}</filename> during IPK packaging.
                            The naming for a normal RPM package and a Multilib IPK package in a
                            <filename>qemux86-64</filename> system resolves to something like
                            <filename>bash_4.1-r2.x86_64.ipk</filename> and
                            <filename>lib32-bash_4.1-rw_x86.ipk</filename>, respectively.
                            </para></listitem>
                        <listitem><para>The IPK deploy folder is not modified with
                            <filename>${MLPREFIX}</filename> because packages with and without
                            the Multilib feature can exist in the same folder due to the
                            <filename>${PN}</filename> differences.</para></listitem>
                        <listitem><para>IPK defines a sanity check for Multilib installation
                            using certain rules for file comparison, overridden, etc.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>
        </section>

        <section id='installing-multiple-versions-of-the-same-library'>
            <title>Installing Multiple Versions of the Same Library</title>

            <para>
                Situations can exist where you need to install and use
                multiple versions of the same library on the same system
                at the same time.
                These situations almost always exist when a library API
                changes and you have multiple pieces of software that
                depend on the separate versions of the library.
                To accommodate these situations, you can install multiple
                versions of the same library in parallel on the same system.
            </para>

            <para>
                The process is straightforward as long as the libraries use
                proper versioning.
                With properly versioned libraries, all you need to do to
                individually specify the libraries is create separate,
                appropriately named recipes where the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink> part of the
                name includes a portion that differentiates each library version
                (e.g.the major part of the version number).
                Thus, instead of having a single recipe that loads one version
                of a library (e.g. <filename>clutter</filename>), you provide
                multiple recipes that result in different versions
                of the libraries you want.
                As an example, the following two recipes would allow the
                two separate versions of the <filename>clutter</filename>
                library to co-exist on the same system:
                <literallayout class='monospaced'>
     clutter-1.6_1.6.20.bb
     clutter-1.8_1.8.4.bb
                </literallayout>
                Additionally, if you have other recipes that depend on a given
                library, you need to use the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
                variable to create the dependency.
                Continuing with the same example, if you want to have a recipe
                depend on the 1.8 version of the <filename>clutter</filename>
                library, use the following in your recipe:
                <literallayout class='monospaced'>
     DEPENDS = "clutter-1.8"
                </literallayout>
            </para>
        </section>
    </section>

    <section id='enabling-gobject-introspection-support'>
        <title>Enabling GObject Introspection Support</title>

        <para>
            <ulink url='https://wiki.gnome.org/Projects/GObjectIntrospection'>GObject introspection</ulink>
            is the standard mechanism for accessing GObject-based software
            from runtime environments.
            GObject is a feature of the GLib library that provides an object
            framework for the GNOME desktop and related software.
            GObject Introspection adds information to GObject that allows
            objects created within it to be represented across different
            programming languages.
            If you want to construct GStreamer pipelines using Python, or
            control UPnP infrastructure using Javascript and GUPnP,
            GObject introspection is the only way to do it.
        </para>

        <para>
            This section describes the Yocto Project support for generating
            and packaging GObject introspection data.
            GObject introspection data is a description of the
            API provided by libraries built on top of GLib framework,
            and, in particular, that framework's GObject mechanism.
            GObject Introspection Repository (GIR) files go to
            <filename>-dev</filename> packages,
            <filename>typelib</filename> files go to main packages as they
            are packaged together with libraries that are introspected.
        </para>

        <para>
            The data is generated when building such a library, by linking
            the library with a small executable binary that asks the library
            to describe itself, and then executing the binary and
            processing its output.
        </para>

        <para>
            Generating this data in a cross-compilation environment
            is difficult because the library is produced for the target
            architecture, but its code needs to be executed on the build host.
            This problem is solved with the OpenEmbedded build system by
            running the code through QEMU, which allows precisely that.
            Unfortunately, QEMU does not always work perfectly as mentioned
            in the xxx section.
        </para>

        <section id='enabling-the-generation-of-introspection-data'>
            <title>Enabling the Generation of Introspection Data</title>

            <para>
                Enabling the generation of introspection data (GIR files)
                in your library package involves the following:
                <orderedlist>
                    <listitem><para>
                        Inherit the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-gobject-introspection'><filename>gobject-introspection</filename></ulink>
                        class.
                        </para></listitem>
                    <listitem><para>
                        Make sure introspection is not disabled anywhere in
                        the recipe or from anything the recipe includes.
                        Also, make sure that "gobject-introspection-data" is
                        not in
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES_BACKFILL_CONSIDERED'><filename>DISTRO_FEATURES_BACKFILL_CONSIDERED</filename></ulink>
                        and that "qemu-usermode" is not in
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_FEATURES_BACKFILL_CONSIDERED'><filename>MACHINE_FEATURES_BACKFILL_CONSIDERED</filename></ulink>.
                        If either of these conditions exist, nothing will
                        happen.
                        </para></listitem>
                    <listitem><para>
                        Try to build the recipe.
                        If you encounter build errors that look like
                        something is unable to find
                        <filename>.so</filename> libraries, check where these
                        libraries are located in the source tree and add
                        the following to the recipe:
                        <literallayout class='monospaced'>
     GIR_EXTRA_LIBS_PATH = "${B}/<replaceable>something</replaceable>/.libs"
                        </literallayout>
                        <note>
                            See recipes in the <filename>oe-core</filename>
                            repository that use that
                            <filename>GIR_EXTRA_LIBS_PATH</filename> variable
                            as an example.
                        </note>
                        </para></listitem>
                    <listitem><para>
                        Look for any other errors, which probably mean that
                        introspection support in a package is not entirely
                        standard, and thus breaks down in a cross-compilation
                        environment.
                        For such cases, custom-made fixes are needed.
                        A good place to ask and receive help in these cases
                        is the
                        <ulink url='&YOCTO_DOCS_REF_URL;#resources-mailinglist'>Yocto Project mailing lists</ulink>.
                        </para></listitem>
                </orderedlist>
                <note>
                    Using a library that no longer builds against the latest
                    Yocto Project release and prints introspection related
                    errors is a good candidate for the previous procedure.
                </note>
            </para>
        </section>

        <section id='disabling-the-generation-of-introspection-data'>
            <title>Disabling the Generation of Introspection Data</title>

            <para>
                You might find that you do not want to generate
                introspection data.
                Or, perhaps QEMU does not work on your build host and
                target architecture combination.
                If so, you can use either of the following methods to
                disable GIR file generations:
                <itemizedlist>
                    <listitem><para>
                        Add the following to your distro configuration:
                        <literallayout class='monospaced'>
     DISTRO_FEATURES_BACKFILL_CONSIDERED = "gobject-introspection-data"
                        </literallayout>
                        Adding this statement disables generating
                        introspection data using QEMU but will still enable
                        building introspection tools and libraries
                        (i.e. building them does not require the use of QEMU).
                        </para></listitem>
                    <listitem><para>
                        Add the following to your machine configuration:
                        <literallayout class='monospaced'>
     MACHINE_FEATURES_BACKFILL_CONSIDERED = "qemu-usermode"
                        </literallayout>
                        Adding this statement disables the use of QEMU
                        when building packages for your machine.
                        Currently, this feature is used only by introspection
                        recipes and has the same effect as the previously
                        described option.
                        <note>
                            Future releases of the Yocto Project might have
                            other features affected by this option.
                        </note>
                        </para></listitem>
                </itemizedlist>
                If you disable introspection data, you can still
                obtain it through other means such as copying the data
                from a suitable sysroot, or by generating it on the
                target hardware.
                The OpenEmbedded build system does not currently
                provide specific support for these techniques.
            </para>
        </section>

        <section id='testing-that-introspection-works-in-an-image'>
            <title>Testing that Introspection Works in an Image</title>

            <para>
                Use the following procedure to test if generating
                introspection data is working in an image:
                <orderedlist>
                    <listitem><para>
                        Make sure that "gobject-introspection-data" is not in
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES_BACKFILL_CONSIDERED'><filename>DISTRO_FEATURES_BACKFILL_CONSIDERED</filename></ulink>
                        and that "qemu-usermode" is not in
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_FEATURES_BACKFILL_CONSIDERED'><filename>MACHINE_FEATURES_BACKFILL_CONSIDERED</filename></ulink>.
                        </para></listitem>
                    <listitem><para>
                        Build <filename>core-image-sato</filename>.
                        </para></listitem>
                    <listitem><para>
                        Launch a Terminal and then start Python in the
                        terminal.
                        </para></listitem>
                    <listitem><para>
                        Enter the following in the terminal:
                        <literallayout class='monospaced'>
     >>> from gi.repository import GLib
     >>> GLib.get_host_name()
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        For something a little more advanced, enter the
                        following:
                        <literallayout class='monospaced'>
     http://python-gtk-3-tutorial.readthedocs.org/en/latest/introduction.html
                        </literallayout>
                        </para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='known-issues'>
            <title>Known Issues</title>

            <para>
                The following know issues exist for
                GObject Introspection Support:
                <itemizedlist>
                    <listitem><para>
                        <filename>qemu-ppc64</filename> immediately crashes.
                        Consequently, you cannot build introspection data on
                        that architecture.
                        </para></listitem>
                    <listitem><para>
                        x32 is not supported by QEMU.
                        Consequently, introspection data is disabled.
                        </para></listitem>
                    <listitem><para>
                        musl causes transient GLib binaries to crash on
                        assertion failures.
                        Consequently, generating introspection data is
                        disabled.
                        </para></listitem>
                    <listitem><para>
                        Because QEMU is not able to run the binaries correctly,
                        introspection is disabled for some specific packages
                        under specific architectures (e.g.
                        <filename>gcr</filename>,
                        <filename>libsecret</filename>, and
                        <filename>webkit</filename>).
                        </para></listitem>
                    <listitem><para>
                        Using QEMU in usermode might not work properly when
                        running 64-bit binaries under 32-bit host machines.
                        In particular, "qemumips64" is known to not work under
                        i686.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>
    </section>

    <section id='dev-optionally-using-an-external-toolchain'>
        <title>Optionally Using an External Toolchain</title>

        <para>
            You might want to use an external toolchain as part of your
            development.
            If this is the case, the fundamental steps you need to accomplish
            are as follows:
            <itemizedlist>
                <listitem><para>
                    Understand where the installed toolchain resides.
                    For cases where you need to build the external toolchain,
                    you would need to take separate steps to build and install
                    the toolchain.
                    </para></listitem>
                <listitem><para>
                    Make sure you add the layer that contains the toolchain to
                    your <filename>bblayers.conf</filename> file through the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-BBLAYERS'><filename>BBLAYERS</filename></ulink>
                    variable.
                    </para></listitem>
                <listitem><para>
                    Set the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTERNAL_TOOLCHAIN'><filename>EXTERNAL_TOOLCHAIN</filename></ulink>
                    variable in your <filename>local.conf</filename> file
                    to the location in which you installed the toolchain.
                    </para></listitem>
            </itemizedlist>
            A good example of an external toolchain used with the Yocto Project
            is <trademark class='registered'>Mentor Graphics</trademark>
            Sourcery G++ Toolchain.
            You can see information on how to use that particular layer in the
            <filename>README</filename> file at
            <ulink url='http://github.com/MentorEmbedded/meta-sourcery/'></ulink>.
            You can find further information by reading about the
            <ulink url='&YOCTO_DOCS_REF_URL;#var-TCMODE'><filename>TCMODE</filename></ulink>
            variable in the Yocto Project Reference Manual's variable glossary.
        </para>
    </section>

    <section id='creating-partitioned-images'>
        <title>Creating Partitioned Images</title>

        <para>
            Creating an image for a particular hardware target using the
            OpenEmbedded build system does not necessarily mean you can boot
            that image as is on your device.
            Physical devices accept and boot images in various ways depending
            on the specifics of the device.
            Usually, information about the hardware can tell you what image
            format the device requires.
            Should your device require multiple partitions on an SD card, flash,
            or an HDD, you can use the OpenEmbedded Image Creator,
	        <filename>wic</filename>, to create the properly partitioned image.
        </para>

        <para>
            The <filename>wic</filename> command generates partitioned images
            from existing OpenEmbedded build artifacts.
            Image generation is driven by partitioning commands contained
            in an Openembedded kickstart file (<filename>.wks</filename>)
            specified either directly on the command line or as one of a
            selection of canned <filename>.wks</filename> files as shown
            with the <filename>wic list images</filename> command in the
            "<link linkend='using-a-provided-kickstart_file'>Using an Existing Kickstart File</link>"
            section.
            When applied to a given set of build artifacts, the result is an
            image or set of images that can be directly written onto media and
            used on a particular system.
        </para>

        <para>
	        The <filename>wic</filename> command and the infrastructure
	        it is based on is by definition incomplete.
            Its purpose is to allow the generation of customized images,
            and as such was designed to be completely extensible through a
            plug-in interface.
            See the
            "<link linkend='openembedded-kickstart-plugins'>Plug-ins</link>"
            section for information on these plug-ins.
	    </para>

        <para>
            This section provides some background information on
            <filename>wic</filename>, describes what you need to have in
            place to run the tool, provides instruction on how to use
            <filename>wic</filename>, and provides several examples.
        </para>

        <section id='wic-background'>
            <title>Background</title>

            <para>
                This section provides some background on the
                <filename>wic</filename> utility.
                While none of this information is required to use
                <filename>wic</filename>, you might find it interesting.
                <itemizedlist>
                    <listitem><para>
                        The name "wic" is derived from OpenEmbedded
                        Image Creator (oeic).
                        The "oe" diphthong in "oeic" was promoted to the
                        letter "w", because "oeic" is both difficult to remember and
                        pronounce.</para></listitem>
                    <listitem><para>
                        <filename>wic</filename> is loosely based on the
                        Meego Image Creator (<filename>mic</filename>)
                        framework.
                        The <filename>wic</filename> implementation has been
                        heavily modified to make direct use of OpenEmbedded
                        build artifacts instead of package installation and
                        configuration, which are already incorporated within
                        the OpenEmbedded artifacts.</para></listitem>
                    <listitem><para>
                        <filename>wic</filename> is a completely independent
                        standalone utility that initially provides
                        easier-to-use and more flexible replacements for a
                        couple bits of existing functionality in OE Core's
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-image-live'><filename>image-live</filename></ulink>
                        class and <filename>mkefidisk.sh</filename> script.
                        The difference between
                        <filename>wic</filename> and those examples is
                        that with <filename>wic</filename> the
                        functionality of those scripts is implemented
                        by a general-purpose partitioning language, which is
                        based on Redhat kickstart syntax.</para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='wic-requirements'>
            <title>Requirements</title>

            <para>
                In order to use the <filename>wic</filename> utility
                with the OpenEmbedded Build system, your system needs
                to meet the following requirements:
                <itemizedlist>
                    <listitem><para>The Linux distribution on your
                        development host must support the Yocto Project.
                        See the
                        "<ulink url='&YOCTO_DOCS_REF_URL;#detailed-supported-distros'>Supported Linux Distributions</ulink>"
                        section in the Yocto Project Reference Manual for this
                        list of distributions.</para></listitem>
                    <listitem><para>
                        The standard system utilities, such as
                        <filename>cp</filename>, must be installed on your
                        development host system.
                        </para></listitem>
                    <listitem><para>
                        You need to have the build artifacts already
                        available, which typically means that you must
                        have already created an image using the
                        Openembedded build system (e.g.
                        <filename>core-image-minimal</filename>).
                        While it might seem redundant to generate an image in
                        order to create an image using
                        <filename>wic</filename>, the current version of
                        <filename>wic</filename> requires the artifacts
                        in the form generated by the build system.
                        </para></listitem>
                    <listitem><para>
                        You must build several native tools, which are tools
                        built to run on the build system:
                        <literallayout class='monospaced'>
     $ bitbake parted-native dosfstools-native mtools-native
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        You must have sourced one of the build environment
                        setup scripts (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>)
                        found in the
                        <link linkend='build-directory'>Build Directory</link>.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='wic-getting-help'>
            <title>Getting Help</title>

            <para>
                You can get general help for the <filename>wic</filename>
                by entering the <filename>wic</filename> command by itself
                or by entering the command with a help argument as follows:
                <literallayout class='monospaced'>
     $ wic -h
     $ wic --help
                </literallayout>
            </para>

            <para>
                Currently, <filename>wic</filename> supports two commands:
                <filename>create</filename> and <filename>list</filename>.
                You can get help for these commands as follows:
                <literallayout class='monospaced'>
     $ wic help <replaceable>command</replaceable>
                </literallayout>
            </para>

            <para>
                You can also get detailed help on a number of topics
                from the help system.
                The output of <filename>wic --help</filename>
                displays a list of available help
                topics under a "Help topics" heading.
                You can have the help system display the help text for
                a given topic by prefacing the topic with
                <filename>wic help</filename>:
                <literallayout class='monospaced'>
     $ wic help <replaceable>help_topic</replaceable>
                </literallayout>
            </para>

            <para>
                You can find out more about the images
                <filename>wic</filename> creates using the existing
                kickstart files with the following form of the command:
                <literallayout class='monospaced'>
     $ wic list <replaceable>image</replaceable> help
                </literallayout>
                where <filename><replaceable>image</replaceable></filename> is either
                <filename>directdisk</filename> or
                <filename>mkefidisk</filename>.
            </para>
        </section>

        <section id='operational-modes'>
            <title>Operational Modes</title>

            <para>
	            You can use <filename>wic</filename> in two different
	            modes, depending on how much control you need for
	            specifying the Openembedded build artifacts that are
                used for creating the image: Raw and Cooked:
                <itemizedlist>
                    <listitem><para><emphasis>Raw Mode:</emphasis>
                        You explicitly specify build artifacts through
                        command-line arguments.</para></listitem>
                    <listitem><para><emphasis>Cooked Mode:</emphasis>
                        The current
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
                        setting and image name are used to automatically locate
                        and provide the build artifacts.</para></listitem>
                </itemizedlist>
            </para>

            <para>
                Regardless of the mode you use, you need to have the build
                artifacts ready and available.
                Additionally, the environment must be set up using the
                <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>
                script found in the
                <link linkend='build-directory'>Build Directory</link>.
            </para>

            <section id='raw-mode'>
                <title>Raw Mode</title>

                <para>
                    The general form of the 'wic' command in raw mode is:
                    <literallayout class='monospaced'>
     $ wic create <replaceable>image_name</replaceable>.wks [<replaceable>options</replaceable>] [...]

         Where:

             <replaceable>image_name</replaceable>.wks
                               An OpenEmbedded kickstart file.  You can provide
                               your own custom file or use a file from a set of
                               existing files as described by further options.

             -o <replaceable>OUTDIR</replaceable>, --outdir=<replaceable>OUTDIR</replaceable>
                               The name of a directory in which to create image.

             -i <replaceable>PROPERTIES_FILE</replaceable>, --infile=<replaceable>PROPERTIES_FILE</replaceable>
                               The name of a file containing the values for image
                               properties as a JSON file.

             -e <replaceable>IMAGE_NAME</replaceable>, --image-name=<replaceable>IMAGE_NAME</replaceable>
                               The name of the image from which to use the artifacts
                               (e.g. <filename>core-image-sato</filename>).

             -r <replaceable>ROOTFS_DIR</replaceable>, --rootfs-dir=<replaceable>ROOTFS_DIR</replaceable>
                               The path to the <filename>/rootfs</filename> directory to use as the
                               <filename>.wks</filename> rootfs source.

             -b <replaceable>BOOTIMG_DIR</replaceable>, --bootimg-dir=<replaceable>BOOTIMG_DIR</replaceable>
                               The path to the directory containing the boot artifacts
                               (e.g. <filename>/EFI</filename> or <filename>/syslinux</filename>) to use as the <filename>.wks</filename> bootimg
                               source.

             -k <replaceable>KERNEL_DIR</replaceable>, --kernel-dir=<replaceable>KERNEL_DIR</replaceable>
                               The path to the directory containing the kernel to use
                               in the <filename>.wks</filename> boot image.

             -n <replaceable>NATIVE_SYSROOT</replaceable>, --native-sysroot=<replaceable>NATIVE_SYSROOT</replaceable>
                               The path to the native sysroot containing the tools to use
                               to build the image.

             -s, --skip-build-check
                               Skips the build check.

             -D, --debug
                               Output debug information.
                    </literallayout>
                    <note>
                        You do not need root privileges to run
                        <filename>wic</filename>.
                        In fact, you should not run as root when using the
                        utility.
                    </note>
                </para>
            </section>

            <section id='cooked-mode'>
                <title>Cooked Mode</title>

                <para>
                    The general form of the <filename>wic</filename> command
                    using Cooked Mode is:
                    <literallayout class='monospaced'>
     $ wic create <replaceable>kickstart_file</replaceable> -e <replaceable>image_name</replaceable>

         Where:

             <replaceable>kickstart_file</replaceable>
                               An OpenEmbedded kickstart file. You can provide your own
                               custom file or supplied file.

             <replaceable>image_name</replaceable>
                               Specifies the image built using the OpenEmbedded build
                               system.
                    </literallayout>
                    This form is the simplest and most user-friendly, as it
                    does not require specifying all individual parameters.
                    All you need to provide is your own
                    <filename>.wks</filename> file or one provided with the
                    release.
                </para>
            </section>
        </section>

        <section id='using-a-provided-kickstart_file'>
            <title>Using an Existing Kickstart File</title>

            <para>
                If you do not want to create your own
                <filename>.wks</filename> file, you can use an existing
                file provided by the <filename>wic</filename> installation.
                Use the following command to list the available files:
                <literallayout class='monospaced'>
     $ wic list images
     directdisk Create a 'pcbios' direct disk image
     mkefidisk Create an EFI disk image
                 </literallayout>
                 When you use an existing file, you do not have to use the
                 <filename>.wks</filename> extension.
                 Here is an example in Raw Mode that uses the
                 <filename>directdisk</filename> file:
                 <literallayout class='monospaced'>
     $ wic create directdisk -r <replaceable>rootfs_dir</replaceable> -b <replaceable>bootimg_dir</replaceable> \
           -k <replaceable>kernel_dir</replaceable> -n <replaceable>native_sysroot</replaceable>
                </literallayout>
            </para>

            <para>
                Here are the actual partition language commands
                used in the <filename>mkefidisk.wks</filename> file to generate
                an image:
                <literallayout class='monospaced'>
     # short-description: Create an EFI disk image
     # long-description: Creates a partitioned EFI disk image that the user
     # can directly dd to boot media.

     part /boot --source bootimg-efi --ondisk sda --label msdos --active --align 1024

     part / --source rootfs --ondisk sda --fstype=ext3 --label platform --align 1024

     part swap --ondisk sda --size 44 --label swap1 --fstype=swap

     bootloader  --timeout=10  --append="rootwait rootfstype=ext3 console=ttyPCH0,115200 console=tty0 vmalloc=256MB snd-hda-intel.enable_msi=0"
                </literallayout>
            </para>
        </section>

        <section id='wic-usage-examples'>
            <title>Examples</title>

            <para>
                This section provides several examples that show how to use
                the <filename>wic</filename> utility.
                All the examples assume the list of requirements in the
                "<link linkend='wic-requirements'>Requirements</link>" section
                have been met.
                The examples assume the previously generated image is
                <filename>core-image-minimal</filename>.
            </para>

            <section id='generate-an-image-using-a-provided-kickstart-file'>
                <title>Generate an Image using an Existing Kickstart File</title>

                <para>
                    This example runs in Cooked Mode and uses the
                    <filename>mkefidisk</filename> kickstart file:
                    <literallayout class='monospaced'>
     $ wic create mkefidisk -e core-image-minimal
     Checking basic build environment...
     Done.

     Creating image(s)...

     Info: The new image(s) can be found here:
      /var/tmp/wic/build/mkefidisk-201310230946-sda.direct

     The following build artifacts were used to create the image(s):
      ROOTFS_DIR: /home/trz/yocto/yocto-image/build/tmp/work/minnow-poky-linux/core-image-minimal/1.0-r0/rootfs
      BOOTIMG_DIR: /home/trz/yocto/yocto-image/build/tmp/work/minnow-poky-linux/core-image-minimal/1.0-r0/core-image-minimal-1.0/hddimg
      KERNEL_DIR: /home/trz/yocto/yocto-image/build/tmp/sysroots/minnow/usr/src/kernel
      NATIVE_SYSROOT: /home/trz/yocto/yocto-image/build/tmp/sysroots/x86_64-linux


     The image(s) were created using OE kickstart file:
      /home/trz/yocto/yocto-image/scripts/lib/image/canned-wks/mkefidisk.wks
                    </literallayout>
                    This example shows the easiest way to create an image
                    by running in Cooked Mode and using the
                    <filename>-e</filename> option with an existing kickstart
                    file.
                    All that is necessary is to specify the image used to
                    generate the artifacts.
                    Your <filename>local.conf</filename> needs to have the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
                    variable set to the machine you are using, which is
                    "minnow" in this example.
                </para>

                <para>
                    The output specifies the exact image created as well as
                    where it was created.
                    The output also names the artifacts used and the exact
                    <filename>.wks</filename> script that was used to generate
                    the image.
                    <note>
                        You should always verify the details provided in the
                        output to make sure that the image was indeed created
                        exactly as expected.
                    </note>
                </para>

                <para>
                    Continuing with the example, you can now directly
                    <filename>dd</filename> the image to a USB stick, or
                    whatever media for which you built your image,
                    and boot the resulting media:
                    <literallayout class='monospaced'>
     $ sudo dd if=/var/tmp/wic/build/mkefidisk-201310230946-sda.direct of=/dev/sdb
     [sudo] password for trz:
     182274+0 records in
     182274+0 records out
     93324288 bytes (93 MB) copied, 14.4777 s, 6.4 MB/s
     [trz@empanada ~]$ sudo eject /dev/sdb
                    </literallayout>
                </para>
            </section>

            <section id='using-a-modified-kickstart-file'>
                <title>Using a Modified Kickstart File</title>

                <para>
                    Because <filename>wic</filename> image creation is driven
                    by the kickstart file, it is easy to affect image creation
                    by changing the parameters in the file.
                    This next example demonstrates that through modification
                    of the <filename>directdisk</filename> kickstart file.
                </para>

                <para>
                    As mentioned earlier, you can use the command
                    <filename>wic list images</filename> to show the list
                    of existing kickstart files.
                    The directory in which these files reside is
                    <filename>scripts/lib/image/canned-wks/</filename>
                    located in the
                    <link linkend='source-directory'>Source Directory</link>.
                    Because the available files reside in this directory, you
                    can create and add your own custom files to the directory.
                    Subsequent use of the <filename>wic list images</filename>
                    command would then include your kickstart files.
                </para>

                <para>
                    In this example, the existing
                    <filename>directdisk</filename> file already does most
                    of what is needed.
                    However, for the hardware in this example, the image will
                    need to boot from <filename>sdb</filename> instead of
                    <filename>sda</filename>, which is what the
                    <filename>directdisk</filename> kickstart file uses.
                </para>

                <para>
                    The example begins by making a copy of the
                    <filename>directdisk.wks</filename> file in the
                    <filename>scripts/lib/image/canned-wks</filename>
                    directory and then changing the lines that specify the
                    target disk from which to boot.
                    <literallayout class='monospaced'>
     $ cp /home/trz/yocto/yocto-image/scripts/lib/image/canned-wks/directdisk.wks \
          /home/trz/yocto/yocto-image/scripts/lib/image/canned-wks/directdisksdb.wks
                    </literallayout>
                    Next, the example modifies the
                    <filename>directdisksdb.wks</filename> file and changes all
                    instances of "<filename>--ondisk sda</filename>"
                    to "<filename>--ondisk sdb</filename>".
                    The example changes the following two lines and leaves the
                    remaining lines untouched:
                    <literallayout class='monospaced'>
     part /boot --source bootimg-pcbios --ondisk sdb --label boot --active --align 1024
     part / --source rootfs --ondisk sdb --fstype=ext3 --label platform --align 1024
                    </literallayout>
                    Once the lines are changed, the example generates the
                    <filename>directdisksdb</filename> image.
                    The command points the process at the
                    <filename>core-image-minimal</filename> artifacts for the
                    Next Unit of Computing (nuc)
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
                    the <filename>local.conf</filename>.
                    <literallayout class='monospaced'>
     $ wic create directdisksdb -e core-image-minimal
     Checking basic build environment...
     Done.

     Creating image(s)...

     Info: The new image(s) can be found here:
      /var/tmp/wic/build/directdisksdb-201310231131-sdb.direct

     The following build artifacts were used to create the image(s):
      ROOTFS_DIR: /home/trz/yocto/yocto-image/build/tmp/work/nuc-poky-linux/core-image-minimal/1.0-r0/rootfs
      BOOTIMG_DIR: /home/trz/yocto/yocto-image/build/tmp/sysroots/nuc/usr/share
      KERNEL_DIR: /home/trz/yocto/yocto-image/build/tmp/sysroots/nuc/usr/src/kernel
      NATIVE_SYSROOT: /home/trz/yocto/yocto-image/build/tmp/sysroots/x86_64-linux


     The image(s) were created using OE kickstart file:
      /home/trz/yocto/yocto-image/scripts/lib/image/canned-wks/directdisksdb.wks
                    </literallayout>
                    Continuing with the example, you can now directly
                    <filename>dd</filename> the image to a USB stick, or
                    whatever media for which you built your image,
                    and boot the resulting media:
                    <literallayout class='monospaced'>
     $ sudo dd if=/var/tmp/wic/build/directdisksdb-201310231131-sdb.direct of=/dev/sdb
     86018+0 records in
     86018+0 records out
     44041216 bytes (44 MB) copied, 13.0734 s, 3.4 MB/s
     [trz@empanada tmp]$ sudo eject /dev/sdb
                    </literallayout>
                </para>
            </section>

            <section id='creating-an-image-based-on-core-image-minimal-and-crownbay-noemgd'>
                <title>Creating an Image Based on <filename>core-image-minimal</filename> and <filename>crownbay-noemgd</filename></title>

                <para>
                    This example creates an image based on
                    <filename>core-image-minimal</filename> and a
                    <filename>crownbay-noemgd</filename>
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
                    that works right out of the box.
                    <literallayout class='monospaced'>
     $ wic create directdisk -e core-image-minimal

     Checking basic build environment...
     Done.

     Creating image(s)...

     Info: The new image(s) can be found here:
      /var/tmp/wic/build/directdisk-201309252350-sda.direct

     The following build artifacts were used to create the image(s):

     ROOTFS_DIR: /home/trz/yocto/yocto-image/build/tmp/work/crownbay_noemgd-poky-linux/core-image-minimal/1.0-r0/rootfs
     BOOTIMG_DIR: /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/share
     KERNEL_DIR: /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/src/kernel
     NATIVE_SYSROOT: /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/src/kernel

     The image(s) were created using OE kickstart file:
      /home/trz/yocto/yocto-image/scripts/lib/image/canned-wks/directdisk.wks
                    </literallayout>
                </para>
            </section>

            <section id='using-a-modified-kickstart-file-and-running-in-raw-mode'>
                <title>Using a Modified Kickstart File and Running in Raw Mode</title>

                <para>
                    This next example manually specifies each build artifact
                    (runs in Raw Mode) and uses a modified kickstart file.
                    The example also uses the <filename>-o</filename> option
                    to cause <filename>wic</filename> to create the output
                    somewhere other than the default
                    <filename>/var/tmp/wic</filename> directory:
                    <literallayout class='monospaced'>
     $ wic create ~/test.wks -o /home/trz/testwic --rootfs-dir \
          /home/trz/yocto/yocto-image/build/tmp/work/crownbay_noemgd-poky-linux/core-image-minimal/1.0-r0/rootfs \
          --bootimg-dir /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/share \
          --kernel-dir /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/src/kernel \
          --native-sysroot /home/trz/yocto/yocto-image/build/tmp/sysroots/x86_64-linux

     Creating image(s)...

     Info: The new image(s) can be found here:
      /home/trz/testwic/build/test-201309260032-sda.direct

     The following build artifacts were used to create the image(s):

     ROOTFS_DIR: /home/trz/yocto/yocto-image/build/tmp/work/crownbay_noemgd-poky-linux/core-image-minimal/1.0-r0/rootfs
     BOOTIMG_DIR: /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/share
     KERNEL_DIR: /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/src/kernel
     NATIVE_SYSROOT: /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/src/kernel

     The image(s) were created using OE kickstart file:
      /home/trz/test.wks
                    </literallayout>
                    For this example,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
                    did not have to be specified in the
                    <filename>local.conf</filename> file since the artifact is
                    manually specified.
                </para>
            </section>
        </section>

        <section id='openembedded-kickstart-plugins'>
            <title>Plug-ins</title>

            <para>
	            Plug-ins allow <filename>wic</filename> functionality to
	            be extended and specialized by users.
                This section documents the plugin interface, which is
                currently restricted to source plug ins.
            </para>

            <para>
	            Source plug ins provide a mechanism to customize
	            various aspects of the image generation process in
	            <filename>wic</filename>, mainly the contents of
	            partitions.
	            The plug ins provide a mechanism for mapping values
	            specified in <filename>.wks</filename> files using the
	            <filename>--source</filename> keyword to a
                particular plugin implementation that populates a
                corresponding partition.
            </para>

            <para>
	            A source plugin is created as a subclass of
	            <filename>SourcePlugin</filename>.
                The plugin file containing it is added to
	            <filename>scripts/lib/wic/plugins/source/</filename> to
	            make the plugin implementation available to the
	            <filename>wic</filename> implementation.
                For more information, see
	            <filename>scripts/lib/wic/pluginbase.py</filename>.
            </para>

            <para>
	            Source plugins can also be implemented and added by
	            external layers.
                As such, any plugins found in a
	            <filename>scripts/lib/wic/plugins/source/</filename>
	            directory in an external layer are also made
	            available.
            </para>

            <para>
	            When the <filename>wic</filename> implementation needs
	            to invoke a partition-specific implementation, it looks
	            for the plugin that has the same name as the
	            <filename>--source</filename> parameter given to
                that partition.
                For example, if the partition is set up as follows:
                <literallayout class='monospaced'>
     part /boot --source bootimg-pcbios   ...
                </literallayout>
	            The methods defined as class members of the plugin
	            having the matching <filename>bootimg-pcbios.name</filename>
                class member are used.
            </para>

            <para>
	            To be more concrete, here is the plugin definition that
	            matches a
                <filename>--source bootimg-pcbios</filename> usage,
                along with an example
	            method called by the <filename>wic</filename> implementation
                when it needs to invoke an implementation-specific
	            partition-preparation function:
                <literallayout class='monospaced'>
    class BootimgPcbiosPlugin(SourcePlugin):
        name = 'bootimg-pcbios'

    @classmethod
        def do_prepare_partition(self, part, ...)
                </literallayout>
	            If the subclass itself does not implement a function, a
	            default version in a superclass is located and
	            used, which is why all plugins must be derived from
	            <filename>SourcePlugin</filename>.
            </para>

            <para>
	            The <filename>SourcePlugin</filename> class defines the
	            following methods, which is the current set of methods
	            that can be implemented or overridden by
	            <filename>--source</filename> plugins.
                Any methods not implemented by a
                <filename>SourcePlugin</filename> subclass inherit the
                implementations present in the
	            <filename>SourcePlugin</filename> class.
                For more information, see the
	            <filename>SourcePlugin</filename> source for details:
            </para>

            <para>
                <itemizedlist>
                    <listitem><para><emphasis><filename>do_prepare_partition()</filename>:</emphasis>
                        Called to do the actual content population for a
                        partition.
                        In other words, the method prepares the final
                        partition image that is incorporated into the
                        disk image.
                        </para></listitem>
                    <listitem><para><emphasis><filename>do_configure_partition()</filename>:</emphasis>
                        Called before
                        <filename>do_prepare_partition()</filename>.
                        This method is typically used to create custom
                        configuration files for a partition (e.g. syslinux or
                        grub configuration files).
                        </para></listitem>
                    <listitem><para><emphasis><filename>do_install_disk()</filename>:</emphasis>
                        Called after all partitions have been prepared and
                        assembled into a disk image.
                        This method provides a hook to allow finalization of a
                        disk image, (e.g. writing an MBR).
                        </para></listitem>
                    <listitem><para><emphasis><filename>do_stage_partition()</filename>:</emphasis>
                        Special content-staging hook called before
                        <filename>do_prepare_partition()</filename>.
                        This method is normally empty.</para>
                        <para>Typically, a partition just uses the passed-in
                        parameters (e.g. the unmodified value of
		                <filename>bootimg_dir</filename>).
                        However, in some cases things might need to be
                        more tailored.
                        As an example, certain files might additionally
                        need to be taken from
                        <filename>bootimg_dir + /boot</filename>.
		                This hook allows those files to be staged in a
		                customized fashion.
                        <note>
                            <filename>get_bitbake_var()</filename>
                            allows you to access non-standard variables
                            that you might want to use for this.
                        </note>
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                This scheme is extensible.
                Adding more hooks is a simple matter of adding more
                plugin methods to <filename>SourcePlugin</filename> and
                derived classes.
                The code that then needs to call the plugin methods uses
                <filename>plugin.get_source_plugin_methods()</filename>
                to find the method or methods needed by the call.
                Retrieval of those methods is accomplished
                by filling up a dict with keys
                containing the method names of interest.
                On success, these will be filled in with the actual
                methods.
                Please see the <filename>wic</filename>
                implementation for examples and details.
            </para>
        </section>

        <section id='openembedded-kickstart-wks-reference'>
            <title>OpenEmbedded Kickstart (.wks) Reference</title>

            <para>
                The current <filename>wic</filename> implementation supports
                only the basic kickstart partitioning commands:
                <filename>partition</filename> (or <filename>part</filename>
                for short) and <filename>bootloader</filename>.
                <note>
                    Future updates will implement more commands and options.
                    If you use anything that is not specifically
                    supported, results can be unpredictable.
                </note>
            </para>

            <para>
                The following is a list of the commands, their syntax,
                and meanings.
                The commands are based on the Fedora
                kickstart versions but with modifications to
                reflect <filename>wic</filename> capabilities.
                You can see the original documentation for those commands
                at the following links:
                <itemizedlist>
                    <listitem><para>
                        <ulink url='http://fedoraproject.org/wiki/Anaconda/Kickstart#part_or_partition'>http://fedoraproject.org/wiki/Anaconda/Kickstart#part_or_partition</ulink>
			            </para></listitem>
                    <listitem><para>
                        <ulink url='http://fedoraproject.org/wiki/Anaconda/Kickstart#bootloader'>http://fedoraproject.org/wiki/Anaconda/Kickstart#bootloader</ulink>
			            </para></listitem>
                </itemizedlist>
            </para>

            <section id='command-part-or-partition'>
                <title>Command: part or partition</title>

                <para>
                Either of these commands create a partition on the system
                and uses the following syntax:
                    <literallayout class='monospaced'>
     part [<replaceable>mntpoint</replaceable>]
     partition [<replaceable>mntpoint</replaceable>]
                    </literallayout>
                    If you do not provide
                    <replaceable>mntpoint</replaceable>, wic creates a partition
                    but does not mount it.
                </para>

                <para>
                    The <filename><replaceable>mntpoint</replaceable></filename>
                    is where the
                    partition will be mounted and must be of one of the
                    following forms:
                    <itemizedlist>
                        <listitem><para><filename>/<replaceable>path</replaceable></filename>:
                            For example, <filename>/</filename>,
                            <filename>/usr</filename>, or
                            <filename>/home</filename></para></listitem>
                        <listitem><para><filename>swap</filename>:
                            The created partition is used as swap space.
                            </para></listitem>
                    </itemizedlist>
                </para>

                <para>
                    Specifying a <replaceable>mntpoint</replaceable> causes
                    the partition to automatically be mounted.
                    Wic achieves this by adding entries to the filesystem
                    table (fstab) during image generation.
                    In order for wic to generate a valid fstab, you must
                    also provide one of the <filename>--ondrive</filename>,
                    <filename>--ondisk</filename>, or
                    <filename>--use-uuid</filename> partition options as part
                    of the command.
                    Here is an example using "/" as the mountpoint.
                    The command uses "--ondisk" to force the partition onto
                    the <filename>sdb</filename> disk:
                    <literallayout class='monospaced'>
     part / --source rootfs --ondisk sdb --fstype=ext3 --label platform --align 1024
                    </literallayout>
                </para>

                <para>
                    Here is a list that describes other supported options you
                    can use with the <filename>part</filename> and
                    <filename>partition</filename> commands:
                    <itemizedlist>
                        <listitem><para><emphasis><filename>--size</filename>:</emphasis>
                            The minimum partition size in MBytes.
                            Specify an integer value such as 500.
                            Do not append the number with "MB".
                            You do not need this option if you use
                            <filename>--source</filename>.</para></listitem>
                        <listitem><para><emphasis><filename>--source</filename>:</emphasis>
                            This option is a
                            <filename>wic</filename>-specific option that
                            names the source of the data that populates
                            the partition.
                            The most common value for this option is
                            "rootfs", but you can use any value that maps to
                            a valid source plugin.
                            For information on the source plugins, see the
                            "<link linkend='openembedded-kickstart-plugins'>Plugins</link>"
                            section.</para>
                            <para>If you use
                            <filename>--source rootfs</filename>,
                            <filename>wic</filename> creates a partition as
                            large as needed and to fill it with the contents of
			                the root filesystem pointed to by the
			                <filename>-r</filename> command-line option
			                or the equivalent rootfs derived from the
			                <filename>-e</filename> command-line
			                option.
                            The filesystem type used to create the
                            partition is driven by the value of the
			                <filename>--fstype</filename> option
			                specified for the partition.
                            See the entry on
                            <filename>--fstype</filename> that
                            follows for more information.
			                </para>
                            <para>If you use
                            <filename>--source <replaceable>plugin-name</replaceable></filename>,
                            <filename>wic</filename> creates a partition as
                            large as needed and fills it with the contents of
                            the partition that is generated by the
                            specified plugin name using the data pointed
                            to by the <filename>-r</filename> command-line
                            option or the equivalent rootfs derived from the
			                <filename>-e</filename> command-line
			                option.
                            Exactly what those contents and filesystem type end
                            up being are dependent on the given plugin
                            implementation.
                            </para>
                            <para>If you do not use the
                            <filename>--source</filename> option, the
                            <filename>wic</filename> command creates an empty
                            partition.
                            Consequently, you must use the
                            <filename>--size</filename> option to specify the
                            size of the empty partition.
                            </para></listitem>
                        <listitem><para><emphasis><filename>--ondisk</filename> or <filename>--ondrive</filename>:</emphasis>
                            Forces the partition to be created on a particular
                            disk.</para></listitem>
                        <listitem><para><emphasis><filename>--fstype</filename>:</emphasis>
                            Sets the file system type for the partition.
                            Valid values are:
                            <itemizedlist>
                                <listitem><para><filename>ext4</filename>
                                </para></listitem>
                                <listitem><para><filename>ext3</filename>
                                </para></listitem>
                                <listitem><para><filename>ext2</filename>
                                </para></listitem>
                                <listitem><para><filename>btrfs</filename>
                                </para></listitem>
                                <listitem><para><filename>squashfs</filename>
                                </para></listitem>
                                <listitem><para><filename>swap</filename>
                                </para></listitem>
                            </itemizedlist></para></listitem>
                        <listitem><para><emphasis><filename>--fsoptions</filename>:</emphasis>
                            Specifies a free-form string of options to be
                            used when mounting the filesystem.
                            This string will be copied into the
                            <filename>/etc/fstab</filename> file of the
                            installed system and should be enclosed in
                            quotes.
                            If not specified, the default string
                            is "defaults".
                            </para></listitem>
                        <listitem><para><emphasis><filename>--label label</filename>:</emphasis>
                            Specifies the label to give to the filesystem to
                            be made on the partition.
                            If the given label is already in use by another
                            filesystem, a new label is created for the
                            partition.</para></listitem>
                        <listitem><para><emphasis><filename>--active</filename>:</emphasis>
                            Marks the partition as active.</para></listitem>
                        <listitem><para><emphasis><filename>--align (in KBytes)</filename>:</emphasis>
                            This option is a <filename>wic</filename>-specific
                            option that says to start a partition on an
                            x KBytes boundary.</para></listitem>
                        <listitem><para><emphasis><filename>--no-table</filename>:</emphasis>
                            This option is a <filename>wic</filename>-specific
                            option.
                            Using the option reserves space for the partition
                            and causes it to become populated.
                            However, the partition is not added to the
                            partition table.
                            </para></listitem>
                        <listitem><para><emphasis><filename>--extra-space</filename>:</emphasis>
                            This option is a <filename>wic</filename>-specific
                            option that adds extra space after the space
                            filled by the content of the partition.
                            The final size can go beyond the size specified
                            by the <filename>--size</filename> option.
                            The default value is 10 Mbytes.
                            </para></listitem>
                        <listitem><para><emphasis><filename>--overhead-factor</filename>:</emphasis>
                            This option is a <filename>wic</filename>-specific
                            option that multiplies the size of the partition by
                            the option's value.
                            You must supply a value greater than or equal to
                            "1".
                            The default value is "1.3".
                            </para></listitem>
                        <listitem><para><emphasis><filename>--part-type</filename>:</emphasis>
                            This option is a <filename>wic</filename>-specific
                            option that specifies the partition type globally
                            unique identifier (GUID) for GPT partitions.
                            You can find the list of partition type GUIDs
                            at
                            <ulink url='http://en.wikipedia.org/wiki/GUID_Partition_Table#Partition_type_GUIDs'></ulink>.
                            </para></listitem>
                        <listitem><para><emphasis><filename>--use-uuid</filename>:</emphasis>
                            This option is a <filename>wic</filename>-specific
                            option that causes <filename>wic</filename> to
                            generate a random GUID for the partition.
                            The generated identifier is used in the bootloader
                            configuration to specify the root partition.
                            </para></listitem>
                        <listitem><para><emphasis><filename>--uuid</filename>:</emphasis>
                            This option is a <filename>wic</filename>-specific
                            option that specifies the partition UUID.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>

            <section id='command-bootloader'>
                <title>Command: bootloader</title>

                <para>
                    This command specifies how the boot loader should be
                    configured and supports the following options:
                    <note>
                        Bootloader functionality and boot partitions are
                        implemented by the various
                        <filename>--source</filename>
			            plugins that implement bootloader functionality.
                        The bootloader command essentially provides a means of
                        modifying bootloader configuration.
                    </note>
                    <itemizedlist>
                        <listitem><para><emphasis><filename>--timeout</filename>:</emphasis>
                            Specifies the number of seconds before the
                            bootloader times out and boots the default option.
                            </para></listitem>
                        <listitem><para><emphasis><filename>--append</filename>:</emphasis>
                            Specifies kernel parameters.
                            These parameters will be added to the syslinux
                            <filename>APPEND</filename> or
                            <filename>grub</filename> kernel command line.
                            </para></listitem>
                        <listitem><para><emphasis><filename>--configfile</filename>:</emphasis>
                            Specifies a user-defined configuration file for
                            the bootloader.
                            You can provide a full pathname for the file or
                            a file that exists in the
                            <filename>canned-wks</filename> folder.
                            This option overrides all other bootloader options.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>
        </section>
    </section>

    <section id='configuring-the-kernel'>
        <title>Configuring the Kernel</title>

        <para>
            Configuring the Yocto Project kernel consists of making sure the
            <filename>.config</filename> file has all the right information
            in it for the image you are building.
            You can use the <filename>menuconfig</filename> tool and
            configuration fragments to make sure your
            <filename>.config</filename> file is just how you need it.
            You can also save known configurations in a
            <filename>defconfig</filename> file that the build system can use
            for kernel configuration.
        </para>

        <para>
            This section describes how to use <filename>menuconfig</filename>,
            create and use configuration fragments, and how to interactively
            modify your <filename>.config</filename> file to create the
            leanest kernel configuration file possible.
        </para>

        <para>
            For more information on kernel configuration, see the
            "<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#changing-the-configuration'>Changing the Configuration</ulink>"
            section in the Yocto Project Linux Kernel Development Manual.
        </para>

        <section id='using-menuconfig'>
            <title>Using&nbsp;&nbsp;<filename>menuconfig</filename></title>

            <para>
                The easiest way to define kernel configurations is to set them through the
                <filename>menuconfig</filename> tool.
                This tool provides an interactive method with which
                to set kernel configurations.
                For general information on <filename>menuconfig</filename>, see
                <ulink url='http://en.wikipedia.org/wiki/Menuconfig'></ulink>.
            </para>

            <para>
                To use the <filename>menuconfig</filename> tool in the Yocto Project development
                environment, you must launch it using BitBake.
                Thus, the environment must be set up using the
                <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>
                script found in the
                <link linkend='build-directory'>Build Directory</link>.
                You must also be sure of the state of your build in the
                <link linkend='source-directory'>Source Directory</link>.
                The following commands run <filename>menuconfig</filename>
                assuming the Source Directory's top-level folder is
                <filename>~/poky</filename>:
                <literallayout class='monospaced'>
     $ cd poky
     $ source oe-init-build-env
     $ bitbake linux-yocto -c kernel_configme -f
     $ bitbake linux-yocto -c menuconfig
                </literallayout>
                Once <filename>menuconfig</filename> comes up, its standard
                interface allows you to interactively examine and configure
                all the kernel configuration parameters.
                After making your changes, simply exit the tool and save your
                changes to create an updated version of the
                <filename>.config</filename> configuration file.
            </para>

            <para>
                Consider an example that configures the <filename>linux-yocto-3.14</filename>
                kernel.
                The OpenEmbedded build system recognizes this kernel as
                <filename>linux-yocto</filename>.
                Thus, the following commands from the shell in which you previously sourced the
                environment initialization script cleans the shared state cache and the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>
                directory and then runs <filename>menuconfig</filename>:
                <literallayout class='monospaced'>
     $ bitbake linux-yocto -c menuconfig
                </literallayout>
            </para>

            <para>
                Once <filename>menuconfig</filename> launches, use the interface
                to navigate through the selections to find the configuration settings in
                which you are interested.
                For example, consider the <filename>CONFIG_SMP</filename> configuration setting.
                You can find it at <filename>Processor Type and Features</filename> under
                the configuration selection <filename>Symmetric Multi-processing Support</filename>.
                After highlighting the selection, use the arrow keys to select or deselect
                the setting.
                When you are finished with all your selections, exit out and save them.
            </para>

            <para>
                Saving the selections updates the <filename>.config</filename> configuration file.
                This is the file that the OpenEmbedded build system uses to configure the
                kernel during the build.
                You can find and examine this file in the Build Directory in
                <filename>tmp/work/</filename>.
                The actual <filename>.config</filename> is located in the area where the
                specific kernel is built.
                For example, if you were building a Linux Yocto kernel based on the
                Linux 3.14 kernel and you were building a QEMU image targeted for
                <filename>x86</filename> architecture, the
                <filename>.config</filename> file would be located here:
                <literallayout class='monospaced'>
     poky/build/tmp/work/qemux86-poky-linux/linux-yocto-3.14.11+git1+84f...
        ...656ed30-r1/linux-qemux86-standard-build
                </literallayout>
                <note>
                    The previous example directory is artificially split and many of the characters
                    in the actual filename are omitted in order to make it more readable.
                    Also, depending on the kernel you are using, the exact pathname
                    for <filename>linux-yocto-3.14...</filename> might differ.
                </note>
            </para>

            <para>
                Within the <filename>.config</filename> file, you can see the kernel settings.
                For example, the following entry shows that symmetric multi-processor support
                is not set:
                <literallayout class='monospaced'>
     # CONFIG_SMP is not set
                </literallayout>
            </para>

            <para>
                A good method to isolate changed configurations is to use a combination of the
                <filename>menuconfig</filename> tool and simple shell commands.
                Before changing configurations with <filename>menuconfig</filename>, copy the
                existing <filename>.config</filename> and rename it to something else,
                use <filename>menuconfig</filename> to make
                as many changes as you want and save them, then compare the renamed configuration
                file against the newly created file.
                You can use the resulting differences as your base to create configuration fragments
                to permanently save in your kernel layer.
                <note>
                    Be sure to make a copy of the <filename>.config</filename> and don't just
                    rename it.
                    The build system needs an existing <filename>.config</filename>
                    from which to work.
                </note>
            </para>
        </section>

        <section id='creating-a-defconfig-file'>
            <title>Creating a&nbsp;&nbsp;<filename>defconfig</filename> File</title>

            <para>
                A <filename>defconfig</filename> file is simply a
                <filename>.config</filename> renamed to "defconfig".
                You can use a <filename>defconfig</filename> file
                to retain a known set of kernel configurations from which the
                OpenEmbedded build system can draw to create the final
                <filename>.config</filename> file.
                <note>
                    Out-of-the-box, the Yocto Project never ships a
                    <filename>defconfig</filename> or
                    <filename>.config</filename> file.
                    The OpenEmbedded build system creates the final
                    <filename>.config</filename> file used to configure the
                    kernel.
                </note>
            </para>

            <para>
                To create a <filename>defconfig</filename>, start with a
                complete, working Linux kernel <filename>.config</filename>
                file.
                Copy that file to the appropriate
                <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink><filename>}</filename>
                directory in your layer's
                <filename>recipes-kernel/linux</filename> directory, and rename
                the copied file to "defconfig".
                Then, add the following lines to the linux-yocto
                <filename>.bbappend</filename> file in your layer:
                <literallayout class='monospaced'>
     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
     SRC_URI += "file://defconfig"
                </literallayout>
                The
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                tells the build system how to search for the file, while the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
                extends the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink>
                variable (search directories) to include the
                <filename>${PN}</filename> directory you created to hold the
                configuration changes.
                <note>
                    The build system applies the configurations from the
                    <filename>defconfig</filename> file before applying any
                    subsequent configuration fragments.
                    The final kernel configuration is a combination of the
                    configurations in the <filename>defconfig</filename>
                    file and any configuration fragments you provide.
                    You need to realize that if you have any configuration
                    fragments, the build system applies these on top of and
                    after applying the existing defconfig file configurations.
                </note>
                For more information on configuring the kernel, see the
                "<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#changing-the-configuration'>Changing the Configuration</ulink>"
                and
                "<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#generating-configuration-files'>Generating Configuration Files</ulink>"
                sections, both in the Yocto Project Linux Kernel Development
                Manual.
            </para>
        </section>

        <section id='creating-config-fragments'>
            <title>Creating Configuration Fragments</title>

            <para>
                Configuration fragments are simply kernel options that appear in a file
                placed where the OpenEmbedded build system can find and apply them.
                Syntactically, the configuration statement is identical to what would appear
                in the <filename>.config</filename> file, which is in the
                <link linkend='build-directory'>Build Directory</link>:
                <literallayout class='monospaced'>
     tmp/work/<replaceable>arch</replaceable>-poky-linux/linux-yocto-<replaceable>release_specific_string</replaceable>/linux-<replaceable>arch</replaceable>-<replaceable>build_type</replaceable>
                </literallayout>
            </para>

            <para>
                It is simple to create a configuration fragment.
                For example, issuing the following from the shell creates a configuration fragment
                file named <filename>my_smp.cfg</filename> that enables multi-processor support
                within the kernel:
                <literallayout class='monospaced'>
     $ echo "CONFIG_SMP=y" >> my_smp.cfg
                </literallayout>
                <note>
                    All configuration fragment files must use the
                    <filename>.cfg</filename> extension in order for the
                    OpenEmbedded build system to recognize them as a
                    configuration fragment.
                </note>
            </para>

            <para>
                Where do you put your configuration fragment files?
                You can place these files in the same area pointed to by
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>.
                The OpenEmbedded build system picks up the configuration and
                adds it to the kernel's configuration.
                For example, suppose you had a set of configuration options
                in a file called <filename>myconfig.cfg</filename>.
                If you put that file inside a directory named
                <filename>linux-yocto</filename> that resides in the same
                directory as the kernel's append file and then add a
                <filename>SRC_URI</filename> statement such as the following
                to the kernel's append file, those configuration options
                will be picked up and applied when the kernel is built.
                <literallayout class='monospaced'>
     SRC_URI += "file://myconfig.cfg"
                </literallayout>
            </para>

            <para>
                As mentioned earlier, you can group related configurations into multiple files and
                name them all in the <filename>SRC_URI</filename> statement as well.
                For example, you could group separate configurations specifically for Ethernet and graphics
                into their own files and add those by using a <filename>SRC_URI</filename> statement like the
                following in your append file:
                <literallayout class='monospaced'>
     SRC_URI += "file://myconfig.cfg \
            file://eth.cfg \
            file://gfx.cfg"
                </literallayout>
            </para>
        </section>

        <section id='fine-tuning-the-kernel-configuration-file'>
            <title>Fine-Tuning the Kernel Configuration File</title>

            <para>
                You can make sure the <filename>.config</filename> file is as lean or efficient as
                possible by reading the output of the kernel configuration fragment audit,
                noting any issues, making changes to correct the issues, and then repeating.
            </para>

            <para>
                As part of the kernel build process, the
                <filename>do_kernel_configcheck</filename> task runs.
                This task validates the kernel configuration by checking the final
                <filename>.config</filename> file against the input files.
                During the check, the task produces warning messages for the following
                issues:
                <itemizedlist>
                    <listitem><para>Requested options that did not make the final
                        <filename>.config</filename> file.</para></listitem>
                    <listitem><para>Configuration items that appear twice in the same
                        configuration fragment.</para></listitem>
                    <listitem><para>Configuration items tagged as "required" that were overridden.
                        </para></listitem>
                    <listitem><para>A board overrides a non-board specific option.</para></listitem>
                    <listitem><para>Listed options not valid for the kernel being processed.
                        In other words, the option does not appear anywhere.</para></listitem>
                </itemizedlist>
                <note>
                    The <filename>do_kernel_configcheck</filename> task can
                    also optionally report if an option is overridden during
                    processing.
                </note>
            </para>

            <para>
                For each output warning, a message points to the file
                that contains a list of the options and a pointer to the
                configuration fragment that defines them.
                Collectively, the files are the key to streamlining the
                configuration.
            </para>

            <para>
                To streamline the configuration, do the following:
                <orderedlist>
                    <listitem><para>Start with a full configuration that you
                        know works - it builds and boots successfully.
                        This configuration file will be your baseline.
                        </para></listitem>
                    <listitem><para>Separately run the
                        <filename>do_kernel_configme</filename> and
                        <filename>do_kernel_configcheck</filename> tasks.
                        </para></listitem>
                    <listitem><para>Take the resulting list of files from the
                        <filename>do_kernel_configcheck</filename> task
                        warnings and do the following:
                        <itemizedlist>
                            <listitem><para>
                                Drop values that are redefined in the fragment
                                but do not change the final
                                <filename>.config</filename> file.
                                </para></listitem>
                            <listitem><para>
                                Analyze and potentially drop values from the
                                <filename>.config</filename> file that override
                                required configurations.
                                </para></listitem>
                            <listitem><para>
                                Analyze and potentially remove non-board
                                specific options.
                                </para></listitem>
                            <listitem><para>
                                Remove repeated and invalid options.
                                </para></listitem>
                        </itemizedlist></para></listitem>
                    <listitem><para>
                        After you have worked through the output of the kernel
                        configuration audit, you can re-run the
                        <filename>do_kernel_configme</filename> and
                        <filename>do_kernel_configcheck</filename> tasks to
                        see the results of your changes.
                        If you have more issues, you can deal with them as
                        described in the previous step.
                        </para></listitem>
                </orderedlist>
            </para>

            <para>
                Iteratively working through steps two through four eventually yields
                a minimal, streamlined configuration file.
                Once you have the best <filename>.config</filename>, you can build the Linux
                Yocto kernel.
            </para>
        </section>

        <section id='determining-hardware-and-non-hardware-features-for-the-kernel-configuration-audit-phase'>
            <title>Determining Hardware and Non-Hardware Features for the Kernel Configuration Audit Phase</title>

            <para>
                This section describes part of the kernel configuration audit
                phase that most developers can ignore.
                During this part of the audit phase, the contents of the final
                <filename>.config</filename> file are compared against the
                fragments specified by the system.
                These fragments can be system fragments, distro fragments,
                or user specified configuration elements.
                Regardless of their origin, the OpenEmbedded build system
                warns the user if a specific option is not included in the
                final kernel configuration.
            </para>

            <para>
                In order to not overwhelm the user with configuration warnings,
                by default the system only reports on missing "hardware"
                options because a missing hardware option could mean a boot
                failure or that important hardware is not available.
            </para>

            <para>
                To determine whether or not a given option is "hardware" or
                "non-hardware", the kernel Metadata contains files that
                classify individual or groups of options as either hardware
                or non-hardware.
                To better show this, consider a situation where the
                Yocto Project kernel cache contains the following files:
                <literallayout class='monospaced'>
     kernel-cache/features/drm-psb/hardware.cfg
     kernel-cache/features/kgdb/hardware.cfg
     kernel-cache/ktypes/base/hardware.cfg
     kernel-cache/bsp/mti-malta32/hardware.cfg
     kernel-cache/bsp/fsl-mpc8315e-rdb/hardware.cfg
     kernel-cache/bsp/qemu-ppc32/hardware.cfg
     kernel-cache/bsp/qemuarma9/hardware.cfg
     kernel-cache/bsp/mti-malta64/hardware.cfg
     kernel-cache/bsp/arm-versatile-926ejs/hardware.cfg
     kernel-cache/bsp/common-pc/hardware.cfg
     kernel-cache/bsp/common-pc-64/hardware.cfg
     kernel-cache/features/rfkill/non-hardware.cfg
     kernel-cache/ktypes/base/non-hardware.cfg
     kernel-cache/features/aufs/non-hardware.kcf
     kernel-cache/features/ocf/non-hardware.kcf
     kernel-cache/ktypes/base/non-hardware.kcf
     kernel-cache/ktypes/base/hardware.kcf
     kernel-cache/bsp/qemu-ppc32/hardware.kcf
                </literallayout>
                The following list provides explanations for the various
                files:
                <itemizedlist>
                    <listitem><para><filename>hardware.kcf</filename>:
                        Specifies a list of kernel Kconfig files that contain
                        hardware options only.
                        </para></listitem>
                    <listitem><para><filename>non-hardware.kcf</filename>:
                        Specifies a list of kernel Kconfig files that contain
                        non-hardware options only.
                        </para></listitem>
                    <listitem><para><filename>hardware.cfg</filename>:
                        Specifies a list of kernel
                        <filename>CONFIG_</filename> options that are hardware,
                        regardless of whether or not they are within a Kconfig
                        file specified by a hardware or non-hardware
                        Kconfig file (i.e. <filename>hardware.kcf</filename> or
                        <filename>non-hardware.kcf</filename>).
                        </para></listitem>
                    <listitem><para><filename>non-hardware.cfg</filename>:
                        Specifies a list of kernel
                        <filename>CONFIG_</filename> options that are
                        not hardware, regardless of whether or not they are
                        within a Kconfig file specified by a hardware or
                        non-hardware Kconfig file (i.e.
                        <filename>hardware.kcf</filename> or
                        <filename>non-hardware.kcf</filename>).
                        </para></listitem>
                </itemizedlist>
                Here is a specific example using the
                <filename>kernel-cache/bsp/mti-malta32/hardware.cfg</filename>:
                <literallayout class='monospaced'>
     CONFIG_SERIAL_8250
     CONFIG_SERIAL_8250_CONSOLE
     CONFIG_SERIAL_8250_NR_UARTS
     CONFIG_SERIAL_8250_PCI
     CONFIG_SERIAL_CORE
     CONFIG_SERIAL_CORE_CONSOLE
     CONFIG_VGA_ARB
                </literallayout>
                The kernel configuration audit automatically detects these
                files (hence the names must be exactly the ones discussed here),
                and uses them as inputs when generating warnings about the
                final <filename>.config</filename> file.
            </para>

            <para>
                A user-specified kernel Metadata repository, or recipe space
                feature, can use these same files to classify options that are
                found within its <filename>.cfg</filename> files as hardware
                or non-hardware, to prevent the OpenEmbedded build system from
                producing an error or warning when an option is not in the
                final <filename>.config</filename> file.
            </para>
        </section>
    </section>

    <section id="patching-the-kernel">
        <title>Patching the Kernel</title>

        <para>
            Patching the kernel involves changing or adding configurations to an existing kernel,
            changing or adding recipes to the kernel that are needed to support specific hardware features,
            or even altering the source code itself.
            <note>
                You can use the <filename>yocto-kernel</filename> script
                found in the <link linkend='source-directory'>Source Directory</link>
                under <filename>scripts</filename> to manage kernel patches and configuration.
                See the "<ulink url='&YOCTO_DOCS_BSP_URL;#managing-kernel-patches-and-config-items-with-yocto-kernel'>Managing kernel Patches and Config Items with yocto-kernel</ulink>"
                section in the Yocto Project Board Support Packages (BSP) Developer's Guide for
                more information.</note>
        </para>

        <para>
            This example creates a simple patch by adding some QEMU emulator console
            output at boot time through <filename>printk</filename> statements in the kernel's
            <filename>calibrate.c</filename> source code file.
            Applying the patch and booting the modified image causes the added
            messages to appear on the emulator's console.
        </para>

        <para>
            The example assumes a clean build exists for the <filename>qemux86</filename>
            machine in a
            <link linkend='source-directory'>Source Directory</link>
            named <filename>poky</filename>.
            Furthermore, the <link linkend='build-directory'>Build Directory</link> is
            <filename>build</filename> and is located in <filename>poky</filename> and
            the kernel is based on the Linux 3.4 kernel.
        </para>

        <para>
            Also, for more information on patching the kernel, see the
            "<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#applying-patches'>Applying Patches</ulink>"
            section in the Yocto Project Linux Kernel Development Manual.
        </para>

        <section id='create-a-layer-for-your-changes'>
            <title>Create a Layer for your Changes</title>

            <para>
                The first step is to create a layer so you can isolate your
                changes.
                Rather than use the <filename>yocto-layer</filename> script
                to create the layer, this example steps through the process
                by hand.
                If you want information on the script that creates a general
                layer, see the
                "<link linkend='creating-a-general-layer-using-the-yocto-layer-script'>Creating a General Layer Using the yocto-layer Script</link>"
                section.
            </para>

            <para>
                These two commands create a directory you can use for your
                layer:
                <literallayout class='monospaced'>
     $ cd ~/poky
     $ mkdir meta-mylayer
                </literallayout>
                Creating a directory that follows the Yocto Project layer naming
                conventions sets up the layer for your changes.
                The layer is where you place your configuration files, append
                files, and patch files.
                To learn more about creating a layer and filling it with the
                files you need, see the "<link linkend='understanding-and-creating-layers'>Understanding
                and Creating Layers</link>" section.
            </para>
        </section>

        <section id='finding-the-kernel-source-code'>
            <title>Finding the Kernel Source Code</title>

            <para>
                Each time you build a kernel image, the kernel source code is fetched
                and unpacked into the following directory:
                <literallayout class='monospaced'>
     ${S}/linux
                </literallayout>
                See the "<link linkend='finding-the-temporary-source-code'>Finding Temporary Source Code</link>"
                section and the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink> variable
                for more information about where source is kept during a build.
            </para>

            <para>
                For this example, we are going to patch the
                <filename>init/calibrate.c</filename> file
                by adding some simple console <filename>printk</filename> statements that we can
                see when we boot the image using QEMU.
            </para>
        </section>

        <section id='creating-the-patch'>
            <title>Creating the Patch</title>

            <para>
                Two methods exist by which you can create the patch:
                <link linkend='using-devtool-in-your-workflow'><filename>devtool</filename></link> and
                <link linkend='using-a-quilt-workflow'>Quilt</link>.
                For kernel patches, the Git workflow is more appropriate.
                This section assumes the Git workflow and shows the steps specific to
                this example.
                <orderedlist>
                    <listitem><para><emphasis>Change the working directory</emphasis>:
                        Change to where the kernel source code is before making
                        your edits to the <filename>calibrate.c</filename> file:
                        <literallayout class='monospaced'>
     $ cd ~/poky/build/tmp/work/qemux86-poky-linux/linux-yocto-${PV}-${PR}/linux
                        </literallayout>
                        Because you are working in an established Git repository,
                        you must be in this directory in order to commit your changes
                        and create the patch file.
                        <note>The <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink> and
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink> variables
                            represent the version and revision for the
                            <filename>linux-yocto</filename> recipe.
                            The <filename>PV</filename> variable includes the Git meta and machine
                            hashes, which make the directory name longer than you might
                            expect.
                        </note></para></listitem>
                    <listitem><para><emphasis>Edit the source file</emphasis>:
                        Edit the <filename>init/calibrate.c</filename> file to have the
                        following changes:
                        <literallayout class='monospaced'>
     void calibrate_delay(void)
     {
         unsigned long lpj;
         static bool printed;
         int this_cpu = smp_processor_id();

         printk("*************************************\n");
         printk("*                                   *\n");
         printk("*        HELLO YOCTO KERNEL         *\n");
         printk("*                                   *\n");
         printk("*************************************\n");

     	if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {
               .
               .
               .
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Stage and commit your changes</emphasis>:
                        These Git commands display the modified file, stage it, and then
                        commit the file:
                        <literallayout class='monospaced'>
     $ git status
     $ git add init/calibrate.c
     $ git commit -m "calibrate: Add printk example"
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Generate the patch file</emphasis>:
                        This Git command creates the a patch file named
                        <filename>0001-calibrate-Add-printk-example.patch</filename>
                        in the current directory.
                        <literallayout class='monospaced'>
     $ git format-patch -1
                        </literallayout>
                        </para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='set-up-your-layer-for-the-build'>
            <title>Set Up Your Layer for the Build</title>

            <para>These steps get your layer set up for the build:
                <orderedlist>
                    <listitem><para><emphasis>Create additional structure</emphasis>:
                        Create the additional layer structure:
                        <literallayout class='monospaced'>
     $ cd ~/poky/meta-mylayer
     $ mkdir conf
     $ mkdir recipes-kernel
     $ mkdir recipes-kernel/linux
     $ mkdir recipes-kernel/linux/linux-yocto
                         </literallayout>
                         The <filename>conf</filename> directory holds your configuration files, while the
                         <filename>recipes-kernel</filename> directory holds your append file and
                         your patch file.</para></listitem>
                    <listitem><para><emphasis>Create the layer configuration file</emphasis>:
                        Move to the <filename>meta-mylayer/conf</filename> directory and create
                        the <filename>layer.conf</filename> file as follows:
                        <literallayout class='monospaced'>
     # We have a conf and classes directory, add to BBPATH
     BBPATH .= ":${LAYERDIR}"

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

     BBFILE_COLLECTIONS += "mylayer"
     BBFILE_PATTERN_mylayer = "^${LAYERDIR}/"
     BBFILE_PRIORITY_mylayer = "5"
                         </literallayout>
                         Notice <filename>mylayer</filename> as part of the last three
                         statements.</para></listitem>
                    <listitem><para><emphasis>Create the kernel recipe append file</emphasis>:
                        Move to the <filename>meta-mylayer/recipes-kernel/linux</filename> directory and create
                        the <filename>linux-yocto_3.4.bbappend</filename> file as follows:
                        <literallayout class='monospaced'>
     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"

     SRC_URI += "file://0001-calibrate-Add-printk-example.patch"
                        </literallayout>
                        The <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
                        and <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                        statements enable the OpenEmbedded build system to find the patch file.
                        For more information on using append files, see the
                        "<link linkend='using-bbappend-files'>Using .bbappend Files</link>"
                        section.
                        </para></listitem>
                    <listitem><para><emphasis>Put the patch file in your layer</emphasis>:
                        Move the <filename>0001-calibrate-Add-printk-example.patch</filename> file to
                        the <filename>meta-mylayer/recipes-kernel/linux/linux-yocto</filename>
                        directory.</para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='set-up-for-the-build'>
            <title>Set Up for the Build</title>

            <para>
                Do the following to make sure the build parameters are set up for the example.
                Once you set up these build parameters, they do not have to change unless you
                change the target architecture of the machine you are building:
                <itemizedlist>
                    <listitem><para><emphasis>Build for the correct target architecture:</emphasis> Your
                        selected <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
                        definition within the <filename>local.conf</filename> file in the
                        <link linkend='build-directory'>Build Directory</link>
                        specifies the target architecture used when building the Linux kernel.
                        By default, <filename>MACHINE</filename> is set to
                        <filename>qemux86</filename>, which specifies a 32-bit
                        <trademark class='registered'>Intel</trademark> Architecture
                        target machine suitable for the QEMU emulator.</para></listitem>
                    <listitem><para><emphasis>Identify your <filename>meta-mylayer</filename>
                        layer:</emphasis> The
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-BBLAYERS'><filename>BBLAYERS</filename></ulink>
                        variable in the
                        <filename>bblayers.conf</filename> file found in the
                        <filename>poky/build/conf</filename> directory needs to have the path to your local
                        <filename>meta-mylayer</filename> layer.
                        By default, the <filename>BBLAYERS</filename> variable contains paths to
                        <filename>meta</filename>, <filename>meta-poky</filename>, and
                        <filename>meta-yocto-bsp</filename> in the
                        <filename>poky</filename> Git repository.
                        Add the path to your <filename>meta-mylayer</filename> location:
                        <literallayout class='monospaced'>
     BBLAYERS ?= " \
       $HOME/poky/meta \
       $HOME/poky/meta-poky \
       $HOME/poky/meta-yocto-bsp \
       $HOME/poky/meta-mylayer \
       "
                        </literallayout></para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='build-the-modified-qemu-kernel-image'>
            <title>Build the Modified QEMU Kernel Image</title>

            <para>
                The following steps build your modified kernel image:
                <orderedlist>
                    <listitem><para><emphasis>Be sure your build environment is initialized</emphasis>:
                        Your environment should be set up since you previously sourced
                        the
                        <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>
                        script.
                        If it is not, source the script again from <filename>poky</filename>.
                        <literallayout class='monospaced'>
     $ cd ~/poky
     $ source &OE_INIT_FILE;
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Clean up</emphasis>:
                        Be sure to clean the shared state out by using BitBake
                        to run from within the Build Directory the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-cleansstate'><filename>do_cleansstate</filename></ulink>
                        task as follows:
                        <literallayout class='monospaced'>
     $ bitbake -c cleansstate linux-yocto
                        </literallayout></para>
                        <para>
                           <note>
                               Never remove any files by hand from the
                               <filename>tmp/deploy</filename>
                               directory inside the
                               <link linkend='build-directory'>Build Directory</link>.
                               Always use the various BitBake clean tasks to
                               clear out previous build artifacts.
                               For information on the clean tasks, see the
                               "<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-clean'><filename>do_clean</filename></ulink>",
                               "<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-cleanall'><filename>do_cleanall</filename></ulink>",
                               and
                               "<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-cleansstate'><filename>do_cleansstate</filename></ulink>"
                               sections all in the Yocto Project Reference
                               Manual.
                           </note>
                        </para></listitem>
                    <listitem><para><emphasis>Build the image</emphasis>:
                        Next, build the kernel image using this command:
                        <literallayout class='monospaced'>
     $ bitbake -k linux-yocto
                        </literallayout></para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='boot-the-image-and-verify-your-changes'>
            <title>Boot the Image and Verify Your Changes</title>

            <para>
                These steps boot the image and allow you to see the changes
                <orderedlist>
                    <listitem><para><emphasis>Boot the image</emphasis>:
                        Boot the modified image in the QEMU emulator
                        using this command:
                        <literallayout class='monospaced'>
     $ runqemu qemux86
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Verify the changes</emphasis>:
                        Log into the machine using <filename>root</filename> with no password and then
                        use the following shell command to scroll through the console's boot output.
                        <literallayout class='monospaced'>
     # dmesg | less
                        </literallayout>
                        You should see the results of your <filename>printk</filename> statements
                        as part of the output.</para></listitem>
                </orderedlist>
            </para>
        </section>
    </section>

    <section id='making-images-more-secure'>
        <title>Making Images More Secure</title>

        <para>
            Security is of increasing concern for embedded devices.
            Consider the issues and problems discussed in just this
            sampling of work found across the Internet:
            <itemizedlist>
                <listitem><para><emphasis>
                    "<ulink url='https://www.schneier.com/blog/archives/2014/01/security_risks_9.html'>Security Risks of Embedded Systems</ulink>"</emphasis>
                    by Bruce Schneier
                    </para></listitem>
                <listitem><para><emphasis>
                    "<ulink url='http://internetcensus2012.bitbucket.org/paper.html'>Internet Census 2012</ulink>"</emphasis>
                    by Carna Botnet</para></listitem>
                <listitem><para><emphasis>
                    "<ulink url='http://elinux.org/images/6/6f/Security-issues.pdf'>Security Issues for Embedded Devices</ulink>"</emphasis>
                    by Jake Edge
                    </para></listitem>
            </itemizedlist>
        </para>

        <para>
            When securing your image is of concern, there are steps, tools,
            and variables that you can consider to help you reach the
            security goals you need for your particular device.
            Not all situations are identical when it comes to making an
            image secure.
            Consequently, this section provides some guidance and suggestions
            for consideration when you want to make your image more secure.
            <note>
                Because the security requirements and risks are
                different for every type of device, this section cannot
                provide a complete reference on securing your custom OS.
                It is strongly recommended that you also consult other sources
                of information on embedded Linux system hardening and on
                security.
            </note>
        </para>

        <section id='general-considerations'>
            <title>General Considerations</title>

            <para>
                General considerations exist that help you create more
                secure images.
                You should consider the following suggestions to help
                make your device more secure:
                <itemizedlist>
                    <listitem><para>
                        Scan additional code you are adding to the system
                        (e.g. application code) by using static analysis
                        tools.
                        Look for buffer overflows and other potential
                        security problems.
                    </para></listitem>
                    <listitem><para>
                        Pay particular attention to the security for
                        any web-based administration interface.
                        </para>
                        <para>Web interfaces typically need to perform
                        administrative functions and tend to need to run with
                        elevated privileges.
                        Thus, the consequences resulting from the interface's
                        security becoming compromised can be serious.
                        Look for common web vulnerabilities such as
                        cross-site-scripting (XSS), unvalidated inputs,
                        and so forth.</para>
                        <para>As with system passwords, the default credentials
                        for accessing a web-based interface should not be the
                        same across all devices.
                        This is particularly true if the interface is enabled
                        by default as it can be assumed that many end-users
                        will not change the credentials.
                    </para></listitem>
                    <listitem><para>
                        Ensure you can update the software on the device to
                        mitigate vulnerabilities discovered in the future.
                        This consideration especially applies when your
                        device is network-enabled.
                    </para></listitem>
                    <listitem><para>
                        Ensure you remove or disable debugging functionality
                        before producing the final image.
                        For information on how to do this, see the
                        "<link linkend='considerations-specific-to-the-openembedded-build-system'>Considerations Specific to the OpenEmbedded Build System</link>"
                        section.
                        </para></listitem>
                    <listitem><para>
                        Ensure you have no network services listening that
                        are not needed.
                    </para></listitem>
                    <listitem><para>
                        Remove any software from the image that is not needed.
                    </para></listitem>
                    <listitem><para>
                        Enable hardware support for secure boot functionality
                        when your device supports this functionality.
                    </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='security-flags'>
            <title>Security Flags</title>

            <para>
                The Yocto Project has security flags that you can enable that
                help make your build output more secure.
                The security flags are in the
                <filename>meta/conf/distro/include/security_flags.inc</filename>
                file in your
                <link linkend='source-directory'>Source Directory</link>
                (e.g. <filename>poky</filename>).
                <note>
                    Depending on the recipe, certain security flags are enabled
                    and disabled by default.
                </note>
            </para>

            <para>
<!--
                The GCC/LD flags in <filename>security_flags.inc</filename>
                enable more secure code generation.
                By including the <filename>security_flags.inc</filename>
                file, you enable flags to the compiler and linker that cause
                them to generate more secure code.
                <note>
                    The GCC/LD flags are enabled by default in the
                    <filename>poky-lsb</filename> distribution.
                </note>
-->
                Use the following line in your
                <filename>local.conf</filename> file or in your custom
                distribution configuration file to enable the security
                compiler and linker flags for your build:
                <literallayout class='monospaced'>
     require conf/distro/include/security_flags.inc
                </literallayout>
            </para>
        </section>

        <section id='considerations-specific-to-the-openembedded-build-system'>
            <title>Considerations Specific to the OpenEmbedded Build System</title>

            <para>
                You can take some steps that are specific to the
                OpenEmbedded build system to make your images more secure:
                <itemizedlist>
                    <listitem><para>
                        Ensure "debug-tweaks" is not one of your selected
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>.
                        When creating a new project, the default is to provide you
                        with an initial <filename>local.conf</filename> file that
                        enables this feature using the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_IMAGE_FEATURES'><filename>EXTRA_IMAGE_FEATURES</filename></ulink> variable with the line:
                <literallayout class='monospaced'>
     EXTRA_IMAGE_FEATURES = "debug-tweaks"
                </literallayout>
                        To disable that feature, simply comment out that line in your
                        <filename>local.conf</filename> file, or
                        make sure <filename>IMAGE_FEATURES</filename> does not contain
                        "debug-tweaks" before producing your final image.
                        Among other things, leaving this in place sets the
                        root password as blank, which makes logging in for
                        debugging or inspection easy during
                        development but also means anyone can easily log in
                        during production.
                        </para></listitem>
                    <listitem><para>
                        It is possible to set a root password for the image
                        and also to set passwords for any extra users you might
                        add (e.g. administrative or service type users).
                        When you set up passwords for multiple images or
                        users, you should not duplicate passwords.
                        </para>
                        <para>
                        To set up passwords, use the
                        <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-extrausers'><filename>extrausers</filename></ulink>
                        class, which is the preferred method.
                        For an example on how to set up both root and user
                        passwords, see the
                        "<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-extrausers'><filename>extrausers.bbclass</filename></ulink>"
                        section.
                        <note>
                            When adding extra user accounts or setting a
                            root password, be cautious about setting the
                            same password on every device.
                            If you do this, and the password you have set
                            is exposed, then every device is now potentially
                            compromised.
                            If you need this access but want to ensure
                            security, consider setting a different,
                            random password for each device.
                            Typically, you do this as a separate step after
                            you deploy the image onto the device.
                        </note>
                        </para></listitem>
                    <listitem><para>
                        Consider enabling a Mandatory Access Control (MAC)
                        framework such as SMACK or SELinux and tuning it
                        appropriately for your device's usage.
                        You can find more information in the
                        <ulink url='http://git.yoctoproject.org/cgit/cgit.cgi/meta-selinux/'><filename>meta-selinux</filename></ulink>
                        layer.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
            </para>
        </section>

        <section id='tools-for-hardening-your-image'>
            <title>Tools for Hardening Your Image</title>

            <para>
                The Yocto Project provides tools for making your image
                more secure.
                You can find these tools in the
                <filename>meta-security</filename> layer of the
                <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi'>Yocto Project Source Repositories</ulink>.
            </para>
        </section>
    </section>

    <section id='creating-your-own-distribution'>
        <title>Creating Your Own Distribution</title>

        <para>
            When you build an image using the Yocto Project and
            do not alter any distribution
            <link linkend='metadata'>Metadata</link>, you are creating a
            Poky distribution.
            If you wish to gain more control over package alternative
            selections, compile-time options, and other low-level
            configurations, you can create your own distribution.
        </para>

        <para>
            To create your own distribution, the basic steps consist of
            creating your own distribution layer, creating your own
            distribution configuration file, and then adding any needed
            code and Metadata to the layer.
            The following steps provide some more detail:
            <itemizedlist>
                <listitem><para><emphasis>Create a layer for your new distro:</emphasis>
                    Create your distribution layer so that you can keep your
                    Metadata and code for the distribution separate.
                    It is strongly recommended that you create and use your own
                    layer for configuration and code.
                    Using your own layer as compared to just placing
                    configurations in a <filename>local.conf</filename>
                    configuration file makes it easier to reproduce the same
                    build configuration when using multiple build machines.
                    See the
                    "<link linkend='creating-a-general-layer-using-the-yocto-layer-script'>Creating a General Layer Using the yocto-layer Script</link>"
                    section for information on how to quickly set up a layer.
                    </para></listitem>
                <listitem><para><emphasis>Create the distribution configuration file:</emphasis>
                    The distribution configuration file needs to be created in
                    the <filename>conf/distro</filename> directory of your
                    layer.
                    You need to name it using your distribution name
                    (e.g. <filename>mydistro.conf</filename>).
                    <note>
                        The
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink>
                        variable in your
                        <filename>local.conf</filename> file determines the
                        name of your distribution.
                    </note></para>
                    <para>You can split out parts of your configuration file
                    into include files and then "require" them from within
                    your distribution configuration file.
                    Be sure to place the include files in the
                    <filename>conf/distro/include</filename> directory of
                    your layer.
                    A common example usage of include files would be to
                    separate out the selection of desired version and revisions
                    for individual recipes.
</para>
                    <para>Your configuration file needs to set the following
                    required variables:
                    <literallayout class='monospaced'>
     <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_NAME'><filename>DISTRO_NAME</filename></ulink>
     <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_VERSION'><filename>DISTRO_VERSION</filename></ulink>
                    </literallayout>
                    These following variables are optional and you typically
                    set them from the distribution configuration file:
                    <literallayout class='monospaced'>
     <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></ulink>
     <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_EXTRA_RDEPENDS'><filename>DISTRO_EXTRA_RDEPENDS</filename></ulink>
     <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_EXTRA_RRECOMMENDS'><filename>DISTRO_EXTRA_RRECOMMENDS</filename></ulink>
     <ulink url='&YOCTO_DOCS_REF_URL;#var-TCLIBC'><filename>TCLIBC</filename></ulink>
                    </literallayout>
                    <tip>
                        If you want to base your distribution configuration file
                        on the very basic configuration from OE-Core, you
                        can use
                        <filename>conf/distro/defaultsetup.conf</filename> as
                        a reference and just include variables that differ
                        as compared to <filename>defaultsetup.conf</filename>.
                        Alternatively, you can create a distribution
                        configuration file from scratch using the
                        <filename>defaultsetup.conf</filename> file
                        or configuration files from other distributions
                        such as Poky or Angstrom as references.
                    </tip></para></listitem>
                <listitem><para><emphasis>Provide miscellaneous variables:</emphasis>
                    Be sure to define any other variables for which you want to
                    create a default or enforce as part of the distribution
                    configuration.
                    You can include nearly any variable from the
                    <filename>local.conf</filename> file.
                    The variables you use are not limited to the list in the
                    previous bulleted item.</para></listitem>
                <listitem><para><emphasis>Point to Your distribution configuration file:</emphasis>
                    In your <filename>local.conf</filename> file in the
                    <link linkend='build-directory'>Build Directory</link>,
                    set your
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink>
                    variable to point to your distribution's configuration file.
                    For example, if your distribution's configuration file is
                    named <filename>mydistro.conf</filename>, then you point
                    to it as follows:
                    <literallayout class='monospaced'>
     DISTRO = "mydistro"
                    </literallayout></para></listitem>
                <listitem><para><emphasis>Add more to the layer if necessary:</emphasis>
                    Use your layer to hold other information needed for the
                    distribution:
                    <itemizedlist>
                        <listitem><para>Add recipes for installing
                            distro-specific configuration files that are not
                            already installed by another recipe.
                            If you have distro-specific configuration files
                            that are included by an existing recipe, you should
                            add an append file (<filename>.bbappend</filename>)
                            for those.
                            For general information and recommendations
                            on how to add recipes to your layer, see the
                            "<link linkend='creating-your-own-layer'>Creating Your Own Layer</link>"
                            and
                            "<link linkend='best-practices-to-follow-when-creating-layers'>Best Practices to Follow When Creating Layers</link>"
                            sections.</para></listitem>
                        <listitem><para>Add any image recipes that are specific
                            to your distribution.</para></listitem>
                        <listitem><para>Add a <filename>psplash</filename>
                            append file for a branded splash screen.
                            For information on append files, see the
                            "<link linkend='using-bbappend-files'>Using .bbappend Files</link>"
                            section.</para></listitem>
                        <listitem><para>Add any other append files to make
                            custom changes that are specific to individual
                            recipes.</para></listitem>
                    </itemizedlist></para></listitem>
            </itemizedlist>
        </para>
    </section>

    <section id='creating-a-custom-template-configuration-directory'>
        <title>Creating a Custom Template Configuration Directory</title>

        <para>
            If you are producing your own customized version
            of the build system for use by other users, you might
            want to customize the message shown by the setup script or
            you might want to change the template configuration files (i.e.
            <filename>local.conf</filename> and
            <filename>bblayers.conf</filename>) that are created in
            a new build directory.
        </para>

        <para>
            The OpenEmbedded build system uses the environment variable
            <filename>TEMPLATECONF</filename> to locate the directory
            from which it gathers configuration information that ultimately
            ends up in the
            <link linkend='build-directory'>Build Directory's</link>
            <filename>conf</filename> directory.
            By default, <filename>TEMPLATECONF</filename> is set as
            follows in the <filename>poky</filename> repository:
            <literallayout class='monospaced'>
     TEMPLATECONF=${TEMPLATECONF:-meta-poky/conf}
            </literallayout>
            This is the directory used by the build system to find templates
            from which to build some key configuration files.
            If you look at this directory, you will see the
            <filename>bblayers.conf.sample</filename>,
            <filename>local.conf.sample</filename>, and
            <filename>conf-notes.txt</filename> files.
            The build system uses these files to form the respective
            <filename>bblayers.conf</filename> file,
            <filename>local.conf</filename> file, and display the list of
            BitBake targets when running the setup script.
        </para>

        <para>
            To override these default configuration files with
            configurations you want used within every new
            Build Directory, simply set the
            <filename>TEMPLATECONF</filename> variable to your directory.
            The <filename>TEMPLATECONF</filename> variable is set in the
            <filename>.templateconf</filename> file, which is in the
            top-level
            <link linkend='source-directory'>Source Directory</link>
            folder (e.g. <filename>poky</filename>).
            Edit the <filename>.templateconf</filename> so that it can locate
            your directory.
        </para>

        <para>
            Best practices dictate that you should keep your
            template configuration directory in your custom distribution layer.
            For example, suppose you have a layer named
            <filename>meta-mylayer</filename> located in your home directory
            and you want your template configuration directory named
            <filename>myconf</filename>.
            Changing the <filename>.templateconf</filename> as follows
            causes the OpenEmbedded build system to look in your directory
            and base its configuration files on the
            <filename>*.sample</filename> configuration files it finds.
            The final configuration files (i.e.
            <filename>local.conf</filename> and
            <filename>bblayers.conf</filename> ultimately still end up in
            your Build Directory, but they are based on your
            <filename>*.sample</filename> files.
            <literallayout class='monospaced'>
     TEMPLATECONF=${TEMPLATECONF:-meta-mylayer/myconf}
            </literallayout>
        </para>

        <para>
            Aside from the <filename>*.sample</filename> configuration files,
            the <filename>conf-notes.txt</filename> also resides in the
            default <filename>meta-poky/conf</filename> directory.
            The scripts that set up the build environment
            (i.e.
            <ulink url="&YOCTO_DOCS_REF_URL;#structure-core-script"><filename>&OE_INIT_FILE;</filename></ulink>
            and
            <ulink url="&YOCTO_DOCS_REF_URL;#structure-memres-core-script"><filename>oe-init-build-env-memres</filename></ulink>)
            use this file to display BitBake targets as part of the script
            output.
            Customizing this <filename>conf-notes.txt</filename> file is a
            good way to make sure your list of custom targets appears
            as part of the script's output.
        </para>

        <para>
            Here is the default list of targets displayed as a result of
            running either of the setup scripts:
            <literallayout class='monospaced'>
     You can now run 'bitbake &lt;target&gt;'

     Common targets are:
         core-image-minimal
         core-image-sato
         meta-toolchain
         meta-ide-support
            </literallayout>
        </para>

        <para>
            Changing the listed common targets is as easy as editing your
            version of <filename>conf-notes.txt</filename> in your
            custom template configuration directory and making sure you
            have <filename>TEMPLATECONF</filename> set to your directory.
        </para>
    </section>

    <section id='building-a-tiny-system'>
        <title>Building a Tiny System</title>

        <para>
            Very small distributions have some significant advantages such
            as requiring less on-die or in-package memory (cheaper), better
            performance through efficient cache usage, lower power requirements
            due to less memory, faster boot times, and reduced development
            overhead.
            Some real-world examples where a very small distribution gives
            you distinct advantages are digital cameras, medical devices,
            and small headless systems.
        </para>

        <para>
            This section presents information that shows you how you can
            trim your distribution to even smaller sizes than the
            <filename>poky-tiny</filename> distribution, which is around
            5 Mbytes, that can be built out-of-the-box using the Yocto Project.
        </para>

        <section id='tiny-system-overview'>
            <title>Overview</title>

            <para>
                The following list presents the overall steps you need to
                consider and perform to create distributions with smaller
                root filesystems, achieve faster boot times, maintain your critical
                functionality, and avoid initial RAM disks:
                <itemizedlist>
                    <listitem><para>
                        <link linkend='goals-and-guiding-principles'>Determine your goals and guiding principles.</link>
                        </para></listitem>
                    <listitem><para>
                        <link linkend='understand-what-gives-your-image-size'>Understand what contributes to your image size.</link>
                        </para></listitem>
                    <listitem><para>
                        <link linkend='trim-the-root-filesystem'>Reduce the size of the root filesystem.</link>
                        </para></listitem>
                    <listitem><para>
                        <link linkend='trim-the-kernel'>Reduce the size of the kernel.</link>
                        </para></listitem>
                    <listitem><para>
                        <link linkend='remove-package-management-requirements'>Eliminate packaging requirements.</link>
                        </para></listitem>
                    <listitem><para>
                        <link linkend='look-for-other-ways-to-minimize-size'>Look for other ways to minimize size.</link>
                        </para></listitem>
                    <listitem><para>
                        <link linkend='iterate-on-the-process'>Iterate on the process.</link>
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='goals-and-guiding-principles'>
            <title>Goals and Guiding Principles</title>

            <para>
                Before you can reach your destination, you need to know
                where you are going.
                Here is an example list that you can use as a guide when
                creating very small distributions:
                <itemizedlist>
                    <listitem><para>Determine how much space you need
                        (e.g. a kernel that is 1 Mbyte or less and
                        a root filesystem that is 3 Mbytes or less).
                        </para></listitem>
                    <listitem><para>Find the areas that are currently
                        taking 90% of the space and concentrate on reducing
                        those areas.
                        </para></listitem>
                    <listitem><para>Do not create any difficult "hacks"
                        to achieve your goals.</para></listitem>
                    <listitem><para>Leverage the device-specific
                        options.</para></listitem>
                    <listitem><para>Work in a separate layer so that you
                        keep changes isolated.
                        For information on how to create layers, see
                        the "<link linkend='understanding-and-creating-layers'>Understanding and Creating Layers</link>" section.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='understand-what-gives-your-image-size'>
            <title>Understand What Contributes to Your Image Size</title>

            <para>
                It is easiest to have something to start with when creating
                your own distribution.
                You can use the Yocto Project out-of-the-box to create the
                <filename>poky-tiny</filename> distribution.
                Ultimately, you will want to make changes in your own
                distribution that are likely modeled after
                <filename>poky-tiny</filename>.
                <note>
                    To use <filename>poky-tiny</filename> in your build,
                    set the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink>
                    variable in your
                    <filename>local.conf</filename> file to "poky-tiny"
                    as described in the
                    "<link linkend='creating-your-own-distribution'>Creating Your Own Distribution</link>"
                    section.
                </note>
            </para>

            <para>
                Understanding some memory concepts will help you reduce the
                system size.
                Memory consists of static, dynamic, and temporary memory.
                Static memory is the TEXT (code), DATA (initialized data
                in the code), and BSS (uninitialized data) sections.
                Dynamic memory represents memory that is allocated at runtime:
                stacks, hash tables, and so forth.
                Temporary memory is recovered after the boot process.
                This memory consists of memory used for decompressing
                the kernel and for the <filename>__init__</filename>
                functions.
            </para>

            <para>
                To help you see where you currently are with kernel and root
                filesystem sizes, you can use two tools found in the
                <link linkend='source-directory'>Source Directory</link> in
                the <filename>scripts/tiny/</filename> directory:
                <itemizedlist>
                    <listitem><para><filename>ksize.py</filename>: Reports
                        component sizes for the kernel build objects.
                        </para></listitem>
                    <listitem><para><filename>dirsize.py</filename>: Reports
                        component sizes for the root filesystem.</para></listitem>
                </itemizedlist>
                This next tool and command help you organize configuration
                fragments and view file dependencies in a human-readable form:
                <itemizedlist>
                    <listitem><para><filename>merge_config.sh</filename>:
                        Helps you manage configuration files and fragments
                        within the kernel.
                        With this tool, you can merge individual configuration
                        fragments together.
                        The tool allows you to make overrides and warns you
                        of any missing configuration options.
                        The tool is ideal for allowing you to iterate on
                        configurations, create minimal configurations, and
                        create configuration files for different machines
                        without having to duplicate your process.</para>
                        <para>The <filename>merge_config.sh</filename> script is
                        part of the Linux Yocto kernel Git repositories
                        (i.e. <filename>linux-yocto-3.14</filename>,
                        <filename>linux-yocto-3.10</filename>,
                        <filename>linux-yocto-3.8</filename>, and so forth)
                        in the
                        <filename>scripts/kconfig</filename> directory.</para>
                        <para>For more information on configuration fragments,
                        see the
                        "<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#generating-configuration-files'>Generating Configuration Files</ulink>"
                        section of the Yocto Project Linux Kernel Development
                        Manual and the "<link linkend='creating-config-fragments'>Creating Configuration Fragments</link>"
                        section, which is in this manual.</para></listitem>
                    <listitem><para><filename>bitbake -u depexp -g <replaceable>bitbake_target</replaceable></filename>:
                        Using the BitBake command with these options brings up
                        a Dependency Explorer from which you can view file
                        dependencies.
                        Understanding these dependencies allows you to make
                        informed decisions when cutting out various pieces of the
                        kernel and root filesystem.</para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='trim-the-root-filesystem'>
            <title>Trim the Root Filesystem</title>

            <para>
                The root filesystem is made up of packages for booting,
                libraries, and applications.
                To change things, you can configure how the packaging happens,
                which changes the way you build them.
                You can also modify the filesystem itself or select a different
                filesystem.
            </para>

            <para>
                First, find out what is hogging your root filesystem by running the
                <filename>dirsize.py</filename> script from your root directory:
                <literallayout class='monospaced'>
     $ cd <replaceable>root-directory-of-image</replaceable>
     $ dirsize.py 100000 > dirsize-100k.log
     $ cat dirsize-100k.log
                </literallayout>
                You can apply a filter to the script to ignore files under
                a certain size.
                The previous example filters out any files below 100 Kbytes.
                The sizes reported by the tool are uncompressed, and thus
                will be smaller by a relatively constant factor in a
                compressed root filesystem.
                When you examine your log file, you can focus on areas of the
                root filesystem that take up large amounts of memory.
            </para>

            <para>
                You need to be sure that what you eliminate does not cripple
                the functionality you need.
                One way to see how packages relate to each other is by using
                the Dependency Explorer UI with the BitBake command:
                <literallayout class='monospaced'>
     $ cd <replaceable>image-directory</replaceable>
     $ bitbake -u depexp -g <replaceable>image</replaceable>
                </literallayout>
                Use the interface to select potential packages you wish to
                eliminate and see their dependency relationships.
            </para>

            <para>
                When deciding how to reduce the size, get rid of packages that
                result in minimal impact on the feature set.
                For example, you might not need a VGA display.
                Or, you might be able to get by with <filename>devtmpfs</filename>
                and <filename>mdev</filename> instead of
                <filename>udev</filename>.
            </para>

            <para>
                Use your <filename>local.conf</filename> file to make changes.
                For example, to eliminate <filename>udev</filename> and
                <filename>glib</filename>, set the following in the
                local configuration file:
                <literallayout class='monospaced'>
     VIRTUAL-RUNTIME_dev_manager = ""
                </literallayout>
            </para>

            <para>
                Finally, you should consider exactly the type of root
                filesystem you need to meet your needs while also reducing
                its size.
                For example, consider <filename>cramfs</filename>,
                <filename>squashfs</filename>, <filename>ubifs</filename>,
                <filename>ext2</filename>, or an <filename>initramfs</filename>
                using <filename>initramfs</filename>.
                Be aware that <filename>ext3</filename> requires a 1 Mbyte
                journal.
                If you are okay with running read-only, you do not need this
                journal.
            </para>

            <note>
                After each round of elimination, you need to rebuild your
                system and then use the tools to see the effects of your
                reductions.
            </note>


        </section>

        <section id='trim-the-kernel'>
            <title>Trim the Kernel</title>

            <para>
                The kernel is built by including policies for hardware-independent
                aspects.
                What subsystems do you enable?
                For what architecture are you building?
                Which drivers do you build by default?
                <note>You can modify the kernel source if you want to help
                    with boot time.
                </note>
            </para>

            <para>
                Run the <filename>ksize.py</filename> script from the top-level
                Linux build directory to get an idea of what is making up
                the kernel:
                <literallayout class='monospaced'>
     $ cd <replaceable>top-level-linux-build-directory</replaceable>
     $ ksize.py > ksize.log
     $ cat ksize.log
                </literallayout>
                When you examine the log, you will see how much space is
                taken up with the built-in <filename>.o</filename> files for
                drivers, networking, core kernel files, filesystem, sound,
                and so forth.
                The sizes reported by the tool are uncompressed, and thus
                will be smaller by a relatively constant factor in a compressed
                kernel image.
                Look to reduce the areas that are large and taking up around
                the "90% rule."
            </para>

            <para>
                To examine, or drill down, into any particular area, use the
                <filename>-d</filename> option with the script:
                <literallayout class='monospaced'>
     $ ksize.py -d > ksize.log
                </literallayout>
                Using this option breaks out the individual file information
                for each area of the kernel (e.g. drivers, networking, and
                so forth).
            </para>

            <para>
                Use your log file to see what you can eliminate from the kernel
                based on features you can let go.
                For example, if you are not going to need sound, you do not
                need any drivers that support sound.
            </para>

            <para>
                After figuring out what to eliminate, you need to reconfigure
                the kernel to reflect those changes during the next build.
                You could run <filename>menuconfig</filename> and make all your
                changes at once.
                However, that makes it difficult to see the effects of your
                individual eliminations and also makes it difficult to replicate
                the changes for perhaps another target device.
                A better method is to start with no configurations using
                <filename>allnoconfig</filename>, create configuration
                fragments for individual changes, and then manage the
                fragments into a single configuration file using
                <filename>merge_config.sh</filename>.
                The tool makes it easy for you to iterate using the
                configuration change and build cycle.
            </para>

            <para>
                Each time you make configuration changes, you need to rebuild
                the kernel and check to see what impact your changes had on
                the overall size.
            </para>
        </section>

        <section id='remove-package-management-requirements'>
            <title>Remove Package Management Requirements</title>

            <para>
                Packaging requirements add size to the image.
                One way to reduce the size of the image is to remove all the
                packaging requirements from the image.
                This reduction includes both removing the package manager
                and its unique dependencies as well as removing the package
                management data itself.
            </para>

            <para>
                To eliminate all the packaging requirements for an image,
                be sure that "package-management" is not part of your
                <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
                statement for the image.
                When you remove this feature, you are removing the package
                manager as well as its dependencies from the root filesystem.
            </para>
        </section>

        <section id='look-for-other-ways-to-minimize-size'>
            <title>Look for Other Ways to Minimize Size</title>

            <para>
                Depending on your particular circumstances, other areas that you
                can trim likely exist.
                The key to finding these areas is through tools and methods
                described here combined with experimentation and iteration.
                Here are a couple of areas to experiment with:
                <itemizedlist>
                    <listitem><para><filename>glibc</filename>:
                        In general, follow this process:
                        <orderedlist>
                            <listitem><para>Remove <filename>glibc</filename>
                                features from
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></ulink>
                                that you think you do not need.</para></listitem>
                            <listitem><para>Build your distribution.
                                </para></listitem>
                            <listitem><para>If the build fails due to missing
                                symbols in a package, determine if you can
                                reconfigure the package to not need those
                                features.
                                For example, change the configuration to not
                                support wide character support as is done for
                                <filename>ncurses</filename>.
                                Or, if support for those characters is needed,
                                determine what <filename>glibc</filename>
                                features provide the support and restore the
                                configuration.
                                </para></listitem>
                            <listitem><para>Rebuild and repeat the process.
                                </para></listitem>
                        </orderedlist></para></listitem>
                    <listitem><para><filename>busybox</filename>:
                        For BusyBox, use a process similar as described for
                        <filename>glibc</filename>.
                        A difference is you will need to boot the resulting
                        system to see if you are able to do everything you
                        expect from the running system.
                        You need to be sure to integrate configuration fragments
                        into Busybox because BusyBox handles its own core
                        features and then allows you to add configuration
                        fragments on top.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='iterate-on-the-process'>
            <title>Iterate on the Process</title>

            <para>
                If you have not reached your goals on system size, you need
                to iterate on the process.
                The process is the same.
                Use the tools and see just what is taking up 90% of the root
                filesystem and the kernel.
                Decide what you can eliminate without limiting your device
                beyond what you need.
            </para>

            <para>
                Depending on your system, a good place to look might be
                Busybox, which provides a stripped down
                version of Unix tools in a single, executable file.
                You might be able to drop virtual terminal services or perhaps
                ipv6.
            </para>
        </section>
    </section>

    <section id='building-images-for-more-than-one-machine'>
        <title>Building Images for More than One Machine</title>

        <para>
            A common scenario developers face is creating images for several
            different machines that use the same software environment.
            In this situation, it is tempting to set the
            tunings and optimization flags for each build specifically for
            the targeted hardware (i.e. "maxing out" the tunings).
            Doing so can considerably add to build times and package feed
            maintenance collectively for the machines.
            For example, selecting tunes that are extremely specific to a
            CPU core used in a system might enable some micro optimizations
            in GCC for that particular system but would otherwise not gain
            you much of a performance difference across the other systems
            as compared to using a more general tuning across all the builds
            (e.g. setting
            <ulink url='var-DEFAULTTUNE'><filename>DEFAULTTUNE</filename></ulink>
            specifically for each machine's build).
            Rather than "max out" each build's tunings, you can take steps that
            cause the OpenEmbedded build system to reuse software across the
            various machines where it makes sense.
        </para>
        <para>
            If build speed and package feed maintenance are considerations,
            you should consider the points in this section that can help you
            optimize your tunings to best consider build times and package
            feed maintenance.
            <itemizedlist>
                <listitem><para><emphasis>Share the Build Directory:</emphasis>
                    If at all possible, share the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>
                    across builds.
                    The Yocto Project supports switching between different
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
                    values in the same <filename>TMPDIR</filename>.
                    This practice is well supported and regularly used by
                    developers when building for multiple machines.
                    When you use the same <filename>TMPDIR</filename> for
                    multiple machine builds, the OpenEmbedded build system can
                    reuse the existing native and often cross-recipes for
                    multiple machines.
                    Thus, build time decreases.
                    <note>
                        If
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink>
                        settings change or fundamental configuration settings
                        such as the filesystem layout, you need to work with
                        a clean <filename>TMPDIR</filename>.
                        Sharing <filename>TMPDIR</filename> under these
                        circumstances might work but since it is not
                        guaranteed, you should use a clean
                        <filename>TMPDIR</filename>.
                    </note>
                    </para></listitem>
                <listitem><para><emphasis>Enable the Appropriate Package Architecture:</emphasis>
                    By default, the OpenEmbedded build system enables three
                    levels of package architectures: "all", "tune" or "package",
                    and "machine".
                    Any given recipe usually selects one of these package
                    architectures (types) for its output.
                    Depending for what a given recipe creates packages, making
                    sure you enable the appropriate package architecture can
                    directly impact the build time.</para>
                    <para>A recipe that just generates scripts can enable
                    "all" architecture because there are no binaries to build.
                    To specifically enable "all" architecture, be sure your
                    recipe inherits the
                    <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-allarch'><filename>allarch</filename></ulink>
                    class.
                    This class is useful for "all" architectures because it
                    configures many variables so packages can be used across
                    multiple architectures.</para>
                    <para>If your recipe needs to generate packages that are
                    machine-specific or when one of the build or runtime
                    dependencies is already machine-architecture dependent,
                    which makes your recipe also machine-architecture dependent,
                    make sure your recipe enables the "machine" package
                    architecture through the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_ARCH'><filename>MACHINE_ARCH</filename></ulink>
                    variable:
                    <literallayout class='monospaced'>
     PACKAGE_ARCH = "${MACHINE_ARCH}"
                    </literallayout>
                    When you do not specifically enable a package
                    architecture through the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_ARCH'><filename>PACKAGE_ARCH</filename></ulink>,
                    The OpenEmbedded build system defaults to the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-TUNE_PKGARCH'><filename>TUNE_PKGARCH</filename></ulink>
                    setting:
                    <literallayout class='monospaced'>
     PACKAGE_ARCH = "${TUNE_PKGARCH}"
                    </literallayout>
                    </para></listitem>
                <listitem><para><emphasis>Choose a Generic Tuning File if Possible:</emphasis>
                    Some tunes are more generic and can run on multiple targets
                    (e.g. an <filename>armv5</filename> set of packages could
                    run on <filename>armv6</filename> and
                    <filename>armv7</filename> processors in most cases).
                    Similarly, <filename>i486</filename> binaries could work
                    on <filename>i586</filename> and higher processors.
                    You should realize, however, that advances on newer
                    processor versions would not be used.</para>
                    <para>If you select the same tune for several different
                    machines, the OpenEmbedded build system reuses software
                    previously built, thus speeding up the overall build time.
                    Realize that even though a new sysroot for each machine is
                    generated, the software is not recompiled and only one
                    package feed exists.
                    </para></listitem>
                <listitem><para><emphasis>Manage Granular Level Packaging:</emphasis>
                    Sometimes cases exist where injecting another level
                    of package architecture beyond the three higher levels
                    noted earlier can be useful.
                    For example, consider the <filename>emgd</filename>
                    graphics stack in the
                    <filename>meta-intel</filename> layer.
                    In this layer, a subset of software exists that is
                    compiled against something different from the rest of the
                    generic packages.
                    You can examine the key code in the
                    <ulink url='http://git.yoctoproject.org/cgit/cgit.cgi'>Source Repositories</ulink>
                    "daisy" branch in
                    <filename>classes/emgd-gl.bbclass</filename>.
                    For a specific set of packages, the code redefines
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_ARCH'><filename>PACKAGE_ARCH</filename></ulink>.
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_EXTRA_ARCHS'><filename>PACKAGE_EXTRA_ARCHS</filename></ulink>
                    is then appended with this extra tune name in
                    <filename>meta-intel-emgd.inc</filename>.
                    The result is that when searching for packages, the
                    build system uses a four-level search and the packages
                    in this new level are preferred as compared to the standard
                    tune.
                    The overall result is that the build system reuses most
                    software from the common tune except for specific cases
                    as needed.
                    </para></listitem>
                <listitem><para><emphasis>Use Tools to Debug Issues:</emphasis>
                    Sometimes you can run into situations where software is
                    being rebuilt when you think it should not be.
                    For example, the OpenEmbedded build system might not be
                    using shared state between machines when you think it
                    should be.
                    These types of situations are usually due to references
                    to machine-specific variables such as
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-SERIAL_CONSOLE'><filename>SERIAL_CONSOLE</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-XSERVER'><filename>XSERVER</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_FEATURES'><filename>MACHINE_FEATURES</filename></ulink>,
                    and so forth in code that is supposed to only be
                    tune-specific or when the recipe depends
                    (<ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'><filename>RRECOMMENDS</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-RSUGGESTS'><filename>RSUGGESTS</filename></ulink>,
                    and so forth) on some other recipe that already has
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_ARCH'><filename>PACKAGE_ARCH</filename></ulink>
                    defined as "${MACHINE_ARCH