# Common Tasks

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.

## Understanding and Creating Layers

The OpenEmbedded build system supports organizing Metadata 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.

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 (`.bbappend`) file, which is described later in this section.

### Layers

The Source Directory 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 `meta-`.

It is not a requirement that a layer name begin with the prefix `meta-`, but it's a commonly accepted standard in the Yocto Project community.

For example, when you set up the Source Directory structure, you will see several layers: `meta`, `meta-hob`, `meta-skeleton`, `meta-yocto`, and `meta-yocto-bsp`. Each of these folders represents a distinct layer.

As another example, if you set up a local copy of the `meta-intel` 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 "BSP Layers" section in the Yocto Project Board Support Package (BSP) Developer's Guide.

### Creating Your Own Layer

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 "Creating a New BSP Layer Using the yocto-bsp Script" section in the Yocto Project Board Support Package (BSP) Developer's Guide and the "Creating a General Layer Using the yocto-layer Script" section further down in this manual.

Follow these general steps to create your layer:

1. Check Existing Layers: 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 `OpenEmbedded Metadata Index` for a list of layers from the OpenEmbedded community that can be used in the Yocto Project.

2. Create a Directory: Create the directory for your layer. While not strictly required, prepend the name of the folder with the string `meta-`. For example:

            meta-mylayer
            meta-GUI_xyz
            meta-mymachine

3. Create a Layer Configuration File: Inside your new layer folder, you need to create a `conf/layer.conf` file. It is easiest to take an existing layer configuration file and copy that to your layer's `conf` directory and then modify the file as needed.

   The `meta-yocto-bsp/conf/layer.conf` file demonstrates the required syntax:

            # 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 = "2"

   Here is an explanation of the example:

   - The configuration and classes directory is appended to `BBPATH`.

     All non-distro layers, which include all BSP layers, are expected to append the layer directory to the `BBPATH`. On the other hand, distro layers, such as `meta-yocto`, can choose to enforce their own precedence over `BBPATH`. For an example of that syntax, see the `layer.conf` file for the `meta-yocto` layer.

   - The recipes for the layers are appended to `BBFILES`.

   - The `BBFILE_COLLECTIONS` variable is then appended with the layer name.

   - The `BBFILE_PATTERN` variable is set to a regular expression and is used to match files from `BBFILES` into a particular layer. In this case, `LAYERDIR` is used to make `BBFILE_PATTERN` match within the layer's path.

   - The `BBFILE_PRIORITY` variable then assigns a priority to the layer. Applying priorities is useful in situations where the same package might appear in multiple layers and allows you to choose what layer should take precedence.

   - The `LAYERVERSION` variable optionally specifies the version of a layer as a single number.

   Note the use of the `LAYERDIR` variable, which expands to the directory of the current layer.

   Through the use of the `BBPATH` variable, BitBake locates `.bbclass` files, configuration files, and files that are included with `include` and `require` statements. For these cases, BitBake uses the first file that matches the name found in `BBPATH`. This is similar to the way the `PATH` variable is used for binaries. We recommend, therefore, that you use unique `.bbclass` and configuration filenames in your custom layer.

4. Add Content: Depending on the type of layer, add the content. If the layer adds support for a machine, add the machine configuration in a `conf/machine/` file within the layer. If the layer adds distro policy, add the distro configuration in a `conf/distro/` file within the layer. If the layer introduces new recipes, put the recipes you need in `recipes-*` subdirectories within the layer.

   In order to be compliant with the Yocto Project, a layer must contain a README file.

### Best Practices to Follow When Creating Layers

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.

#### Avoid "Overlaying" Entire Recipes

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 `.bbappend` files to override only those parts of the original recipe you need to modify.

#### Avoid Duplicating Include Files

Avoid duplicating include files. Use `.bbappend` files for each recipe that uses an include file. Or, if you are introducing a new recipe that requires the included file, use the path relative to the original layer directory to refer to the file. For example, use `require recipes-core/somepackage/somefile.inc` instead of `require somefile.inc`. If you're finding you have to overlay the include file, it could indicate a deficiency in the include file in the layer to which it originally belongs. If this is the case, you need to address that deficiency instead of overlaying the include file.

For example, consider how support plug-ins for the Qt 4 database are configured. The Source Directory does not have MySQL or PostgreSQL. However, OpenEmbedded's layer `meta-oe` does. Consequently, `meta-oe` uses `.bbappend` files to modify the `QT_SQL_DRIVER_FLAGS` variable to enable the appropriate plug-ins. This variable was added to the `qt4.inc` include file in the Source Directory specifically to allow the `meta-oe` layer to be able to control which plug-ins are built.

#### Structure Your Layers

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:

- Modifying Variables to Support a Different Machine: Suppose you have a layer named `meta-one` that adds support for building machine "one". To do so, you use an append file named `base-files.bbappend` and create a dependency on "foo" by altering the `DEPENDS` variable:

           DEPENDS = "foo"

  The dependency is created during any build that includes the layer `meta-one`. However, you might not want this dependency for all machines. For example, suppose you are building for machine "two" but your `bblayers.conf` file has the `meta-one` layer included. During the build, the `base-files` for machine "two" will also have the dependency on `foo`.

  To make sure your changes apply only when building machine "one", use a machine override with the `DEPENDS` statement:

           DEPENDS_one = "foo"

  You should follow the same strategy when using `_append` and `_prepend` operations:

           DEPENDS_append_one = " foo"
           DEPENDS_prepend_one = "foo "

  Avoiding "+=" and "=+" and using machine-specific `_append` and `_prepend` operations is recommended as well.

- Place Machine-Specific Files in Machine-Specific Locations: When you have a base recipe, such as `base-files.bb`, that contains a `SRC_URI` 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 `meta-one/recipes-core/base-files/base-files.bbappend` could extend `FILESPATH` using `FILESEXTRAPATHS` as follows:

           FILESEXTRAPATHS_prepend := "${THISDIR}/${BPN}:"

  The build for machine "one" will pick up your machine-specific file as long as you have the file in `meta-one/recipes-core/base-files/base-files/`. However, if you are building for a different machine and the `bblayers.conf` file includes the `meta-one` layer and the location of your machine-specific file is the first location where that file is found according to `FILESPATH`, builds for all machines will also use that machine-specific file.

  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 `meta-one/recipes-core/base-files/base-files/` as shown above, put it in `meta-one/recipes-core/base-files/base-files/one/`. 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.

  In summary, you need to place all files referenced from `SRC_URI` in a machine-specific subdirectory within the layer in order to restrict those files to machine-specific builds.

#### Other Recommendations

We also recommend the following:

- Store custom layers in a Git repository that uses the `meta-<layer_name>` format.

- Clone the repository alongside other `meta` directories in the Source Directory.

Following these recommendations keeps your Source Directory and its configuration entirely inside the Yocto Project's core base.

### Enabling Your Layer

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 `BBLAYERS` variable in your `conf/bblayers.conf` file, which is found in the Build Directory. The following example shows how to enable a layer named `meta-mylayer`:

         LCONF_VERSION = "6"

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

         BBLAYERS ?= " \
           $HOME/poky/meta \
           $HOME/poky/meta-yocto \
           $HOME/poky/meta-yocto-bsp \
           $HOME/poky/meta-mylayer \
           "

         BBLAYERS_NON_REMOVABLE ?= " \
           $HOME/poky/meta \
           $HOME/poky/meta-yocto \
           "

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

### Using .bbappend Files

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

A `.bbappend` 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 `.bbappend` file resides in your layer, while the main `.bb` recipe file to which you are appending Metadata resides in a different layer.

Append files must have the same root names as their corresponding recipes. For example, the append file `someapp_&DISTRO;.bbappend` must apply to `someapp_&DISTRO;.bb`. 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 `.bbappend` file must be renamed (and possibly updated) as well. During the build process, BitBake displays an error on starting if it detects a `.bbappend` file that does not have a corresponding recipe with a matching name. See the `BB_DANGLINGAPPENDS_WARNONLY` variable for information on how to handle this error.

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.

As an example, consider the main formfactor recipe and a corresponding formfactor append file both from the Source Directory. Here is the main formfactor recipe, which is named `formfactor_0.0.bb` and located in the "meta" layer at `meta/recipes-bsp/formfactor`:

         DESCRIPTION = "Device formfactor information"
         SECTION = "base"
         LICENSE = "MIT"
         LIC_FILES_CHKSUM = "file://${COREBASE}/LICENSE;md5=3f40d7994397109285ec7b81fdeb3b58 \
                             file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420"
         PR = "r41"

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

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

         do_install() {
         	# Only install file if it has a contents
                 install -d ${D}${sysconfdir}/formfactor/
                 install -m 0644 ${S}/config ${D}${sysconfdir}/formfactor/
         	if [ -s "${S}/machconfig" ]; then
         	        install -m 0644 ${S}/machconfig ${D}${sysconfdir}/formfactor/
         	fi
         }

In the main recipe, note the `SRC_URI` variable, which tells the OpenEmbedded build system where to find files during the build.

Following is the append file, which is named `formfactor_0.0.bbappend` and is from the Crown Bay BSP Layer named `meta-intel/meta-crownbay`. The file is in `recipes-bsp/formfactor`:

         FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"

By default, the build system uses the `FILESPATH` variable to locate files. This append file extends the locations by setting the `FILESEXTRAPATHS` variable. Setting this variable in the `.bbappend` file is the most reliable and recommended method for adding directories to the search path used by the build system to find files.

The statement in this example extends the directories to include `${` `THISDIR` `}/${` `PN` `}`, which resolves to a directory named `formfactor` in the same directory in which the append file resides (i.e. `meta-intel/meta-crownbay/recipes-bsp/formfactor/formfactor`. 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.

Using the immediate expansion assignment operator `:=` is important because of the reference to `THISDIR`. The trailing colon character is important as it ensures that items in the list remain colon-separated.

BitBake automatically defines the `THISDIR` variable. You should never set this variable yourself. Using `_prepend` ensures your path will be searched prior to other paths in the final list.

Also, not all append files add extra files. Many append files simply exist to add build options (e.g. `systemd`). For these cases, it is not necessary to use the "_prepend" part of the statement.

### Prioritizing Your Layer

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 `.bbappend` 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.

To specify the layer's priority manually, use the `BBFILE_PRIORITY` variable. For example:

         BBFILE_PRIORITY_mylayer = "1"

It is possible for a recipe with a lower version number `PV` in a layer that has a higher priority to take precedence.

Also, the layer priority does not currently affect the precedence order of `.conf` or `.bbclass` files. Future versions of BitBake might address this.

### Managing Layers

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 `.bbappend` files and their applicable recipes can help to reveal potential problems.

Use the following form when running the layer management tool.

         $ bitbake-layers <command> [arguments]

The following list describes the available commands:

- `help:` Displays general help or help on a specified command.

- `show-layers:` Shows the current configured layers.

- `show-recipes:` Lists available recipes and the layers that provide them.

- `show-overlayed:` Lists overlayed recipes. A recipe is overlayed when a recipe with the same name exists in another layer that has a higher layer priority.

- `show-appends:` Lists `.bbappend` files and the recipe files to which they apply.

- `show-cross-depends:` Lists dependency relationships between recipes that cross layer boundaries.

- `flatten:` 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 `.bbappend` files appended to the corresponding recipes. You might have to perform some manual cleanup of the flattened layer as follows:

  - Non-recipe files (such as patches) are overwritten. The flatten command shows a warning for these files.

  - Anything beyond the normal layer setup has been added to the `layer.conf` file. Only the lowest priority layer's `layer.conf` is used.

  - Overridden and appended items from `.bbappend` files need to be cleaned up. The contents of each `.bbappend` 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 `bitbake-layers` command adds the line `#### bbappended ...` so that you know where the following lines originate:

             ...
             DESCRIPTION = "A useful utility"
             ...
             EXTRA_OECONF = "--enable-something"
             ...

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

             DESCRIPTION = "Customized utility"
             EXTRA_OECONF += "--enable-somethingelse"

    Ideally, you would tidy up these utilities as follows:

             ...
             DESCRIPTION = "Customized utility"
             ...
             EXTRA_OECONF = "--enable-something --enable-somethingelse"
             ...

### Creating a General Layer Using the yocto-layer Script

The `yocto-layer` script simplifies creating a new general layer.

For information on BSP layers, see the "BSP Layers" section in the Yocto Project Board Specific (BSP) Developer's Guide.

The default mode of the script's operation is to prompt you for information needed to generate the layer:

- The layer priority

- Whether or not to create a sample recipe.

- Whether or not to create a sample append file.

Use the `yocto-layer create` sub-command to create a new general layer. In its simplest form, you can create a layer as follows:

         $ yocto-layer create mylayer

The previous example creates a layer named `meta-mylayer` in the current directory.

As the `yocto-layer create` 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 `meta-` to the name you provide.

Minimally, the script creates the following within the layer:

- The `conf` directory: 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. `<layer>.conf`).

- The `COPYING.MIT` file: The copyright and use notice for the software.

- The `README` file: A file describing the contents of your new layer.

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

If you choose to generate a sample append file, the script prompts you for the name for the file and then creates it in `<layer>/recipes-example-bbappend/example-bbappend/`. The script creates a `.bbappend` 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.

The easiest way to see how the `yocto-layer` script works is to experiment with the script. You can also read the usage information by entering the following:

         $ yocto-layer help

Once you create your general layer, you must add it to your `bblayers.conf` file. Here is an example where a layer named `meta-mylayer` is added:

         BBLAYERS = ?" \
            /usr/local/src/yocto/meta \
            /usr/local/src/yocto/meta-yocto \
            /usr/local/src/yocto/meta-yocto-bsp \
            /usr/local/src/yocto/meta-mylayer \
            "

         BBLAYERS_NON_REMOVABLE ?= " \
            /usr/local/src/yocto/meta \
            /usr/local/src/yocto/meta-yocto \
            "

Adding the layer to this file enables the build system to locate the layer during the build.

## Customizing Images

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

### Customizing Images Using `local.conf`

Probably the easiest way to customize an image is to add a package by way of the `local.conf` 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 affect all images at the same time and might not be what you require.

To add a package to your image using the local configuration file, use the `IMAGE_INSTALL` variable with the `_append` operator:

         IMAGE_INSTALL_append = " strace"

Use of the syntax is important - specifically, the space between the quote and the package name, which is `strace` in this example. This space is required since the `_append` operator does not add the space.

Furthermore, you must use `_append` instead of the `+=` 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 `.bbclass` files with operators like `?=`. Using `_append` ensures the operation takes affect.

As shown in its simplest use, `IMAGE_INSTALL_append` affects all images. It is possible to extend the syntax so that the variable applies to a specific image only. Here is an example:

         IMAGE_INSTALL_append_pn-core-image-minimal = " strace"

This example adds `strace` to `core-image-minimal` only.

You can add packages using a similar approach through the `CORE_IMAGE_EXTRA_INSTALL` variable. If you use this variable, only `core-image-*` images are affected.

### Customizing Images Using Custom `IMAGE_FEATURES` and `EXTRA_IMAGE_FEATURES`

Another method for customizing your image is to enable or disable high-level image features by using the `IMAGE_FEATURES` and `EXTRA_IMAGE_FEATURES` variables. Although the functions for both variables are nearly equivalent, best practices dictate using `IMAGE_FEATURES` from within a recipe and using `EXTRA_IMAGE_FEATURES` from within your `local.conf` file, which is found in the Build Directory.

To understand how these features work, the best reference is `meta/classes/core-image.bbclass`. In summary, the file looks at the contents of the `IMAGE_FEATURES` variable and then maps those contents into a set of package groups. Based on this information, the build system automatically adds the appropriate packages to the `IMAGE_INSTALL` variable. Effectively, you are enabling extra features by extending the class or creating a custom class for use with specialized image `.bb` files.

Use the `EXTRA_IMAGE_FEATURES` 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 `IMAGE_FEATURES`. The value of `EXTRA_IMAGE_FEATURES` is added to `IMAGE_FEATURES` within `meta/conf/bitbake.conf`.

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 `core-image-sato` image is configured to use Dropbear. The `core-image-basic` and `core-image-lsb` images both include OpenSSH. The `core-image-minimal` image does not contain an SSH server.

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

See the "Images" section in the Yocto Project Reference Manual for a complete list of image features that ship with the Yocto Project.

### Customizing Images Using Custom .bb Files

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:

         IMAGE_INSTALL = "packagegroup-core-x11-base package1 package2"

         inherit core-image

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 `IMAGE_INSTALL` variable. You must use the OpenEmbedded notation and not the Debian notation for the names (e.g. `eglibc-dev` instead of `libc6-dev`).

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 `core-image-sato` but add the additional package `strace` to the image, copy the `meta/recipes-sato/images/core-image-sato.bb` to a new `.bb` and add the following line to the end of the copy:

         IMAGE_INSTALL += "strace"

### Customizing Images Using Custom Package Groups

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 `meta/recipes-core/packagegroups/packagegroup-core-boot.bb`. The `PACKAGES` variable lists the package group packages you wish to produce. `inherit packagegroup` sets appropriate default values and automatically adds `-dev`, `-dbg`, and `-ptest` complementary packages for every package specified in `PACKAGES`. Note that the inherit line should be towards the top of the recipe, certainly before you set `PACKAGES`. For each package you specify in `PACKAGES`, you can use `RDEPENDS` and `RRECOMMENDS` entries to provide a list of packages the parent task package should contain. Following is an example:

         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-control \
             lttng-viewer"

         RRECOMMENDS_packagegroup-custom-tools = "\
             kernel-module-oprofile"

In the previous example, two package group packages are created with their dependencies and their recommended package dependencies listed: `packagegroup-custom-apps`, and `packagegroup-custom-tools`. To build an image using these package group packages, you need to add `packagegroup-custom-apps` and/or `packagegroup-custom-tools` to `IMAGE_INSTALL`. For other forms of image dependencies see the other areas of this section.

## Writing a Recipe to Add a Package to Your Image

Recipes let you define packages you can add to your image. Writing a recipe means creating a `.bb` file that sets some variables. For information on variables that are useful for recipes and for information about recipe naming issues, see the "Required" section of the Yocto Project Reference Manual.

Before writing a recipe from scratch, it is often useful to check whether someone else has written one already. OpenEmbedded is a good place to look as it has a wider scope and range of packages. Because the Yocto Project aims to be compatible with OpenEmbedded, most recipes you find there should work for you.

For new packages, the simplest way to add a recipe is to base it on a similar pre-existing recipe. The sections that follow provide some examples that show how to add standard types of packages.

When writing shell functions, you need to be aware of BitBake's curly brace parsing. If a recipe uses a closing curly brace within the function and the character has no leading spaces, BitBake produces a parsing error. If you use a pair of curly brace in a shell function, the closing curly brace must not be located at the start of the line without leading spaces.

Here is an example that causes BitBake to produce a parsing error:

         fakeroot create_shar() {
             cat << "EOF" > ${SDK_DEPLOY}/${TOOLCHAIN_OUTPUTNAME}.sh
         usage()
         {
           echo "test"
           ###### The following "}" at the start of the line causes a parsing error ######
         }
         EOF
         }

Writing the recipe this way avoids the error:

         fakeroot create_shar() {
             cat << "EOF" > ${SDK_DEPLOY}/${TOOLCHAIN_OUTPUTNAME}.sh
         usage()
         {
           echo "test"
           ######The following "}" with a leading space at the start of the line avoids the error ######
          }
         EOF
         }

### Single .c File Package (Hello World!)

Building an application from a single file that is stored locally (e.g. under `files/`) requires a recipe that has the file listed in the `SRC_URI` variable. Additionally, you need to manually write the `do_compile` and `do_install` tasks. The `S` variable defines the directory containing the source code, which is set to `WORKDIR` in this case - the directory BitBake uses for the build.

         DESCRIPTION = "Simple helloworld application"
         SECTION = "examples"
         LICENSE = "MIT"
         LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/MIT;md5=0835ade698e0bcf8506ecda2f7b4f302"
         PR = "r0"

         SRC_URI = "file://helloworld.c"

         S = "${WORKDIR}"

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

         do_install() {
         	install -d ${D}${bindir}
         	install -m 0755 helloworld ${D}${bindir}
         }

By default, the `helloworld`, `helloworld-dbg`, and `helloworld-dev` packages are built. For information on how to customize the packaging process, see the "Splitting an Application into Multiple Packages" section.

### Autotooled Package

Applications that use Autotools such as `autoconf` and `automake` require a recipe that has a source archive listed in `SRC_URI` and also inherits Autotools, which instructs BitBake to use the `autotools.bbclass` file, which contains the definitions of all the steps needed to build an Autotool-based application. The result of the build is automatically packaged. And, if the application uses NLS for localization, packages with local information are generated (one package per language). Following is one example: (`hello_2.3.bb`)

         DESCRIPTION = "GNU Helloworld application"
         SECTION = "examples"
         LICENSE = "GPLv2+"
         LIC_FILES_CHKSUM = "file://COPYING;md5=751419260aa954499f7abaabaa882bbe"
         PR = "r0"

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

         inherit autotools gettext

The variable `LIC_FILES_CHKSUM` is used to track source license changes as described in the "Tracking License Changes" section. You can quickly create Autotool-based recipes in a manner similar to the previous example.

### Makefile-Based Package

Applications that use GNU `make` also require a recipe that has the source archive listed in `SRC_URI`. You do not need to add a `do_compile` step since by default BitBake starts the `make` command to compile the application. If you need additional `make` options, you should store them in the `EXTRA_OEMAKE` variable. BitBake passes these options into the `make` GNU invocation. Note that a `do_install` task is still required. Otherwise, BitBake runs an empty `do_install` task by default.

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 `CFLAGS` variable. The following example shows this:

         CFLAGS_prepend = "-I ${S}/include "

In the following example, `mtd-utils` is a makefile-based package:

         DESCRIPTION = "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"

         SRC_URI = "git://git.infradead.org/mtd-utils.git;protocol=git;tag=995cfe51b0a3cf32f381c140bf72b21bf91cef1b \
    	     	file://add-exclusion-to-mkfs-jffs2-git-2.patch"

         S = "${WORKDIR}/git/"

         PR = "r1"

         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}
    	     install -d ${D}${includedir}/mtd/
    	     for f in ${S}/include/mtd/*.h; do
    	     	install -m 0644 $f ${D}${includedir}/mtd/
    	     done
         }

         PARALLEL_MAKE = ""

         BBCLASSEXTEND = "native"

If your sources are available as a tarball instead of a Git repository, you will need to provide the URL to the tarball as well as an `md5` or `sha256` sum of the download. Here is an example:

         SRC_URI="ftp://ftp.infradead.org/pub/mtd-utils/mtd-utils-1.4.9.tar.bz2"
         SRC_URI[md5sum]="82b8e714b90674896570968f70ca778b"

You can generate the `md5` or `sha256` sums by using the `md5sum` or `sha256sum` commands with the target file as the only argument. Here is an example:

         $ md5sum mtd-utils-1.4.9.tar.bz2
         82b8e714b90674896570968f70ca778b mtd-utils-1.4.9.tar.bz2

### Splitting an Application into Multiple Packages

You can use the variables `PACKAGES` and `FILES` to split an application into multiple packages.

Following is an example that uses the `libXpm` 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:

         require xorg-lib-common.inc

         DESCRIPTION = "X11 Pixmap library"
         LICENSE = "X-BSD"
         LIC_FILES_CHKSUM = "file://COPYING;md5=3e07763d16963c3af12db271a31abaa5"
         DEPENDS += "libxext libsm libxt"
         PR = "r3"
         PE = "1"

         XORG_PN = "libXpm"

         PACKAGES =+ "sxpm cxpm"
         FILES_cxpm = "${bindir}/cxpm"
         FILES_sxpm = "${bindir}/sxpm"

In the previous example, we want to ship the `sxpm` and `cxpm` binaries in separate packages. Since `bindir` would be packaged into the main `PN` package by default, we prepend the `PACKAGES` variable so additional package names are added to the start of list. This results in the extra `FILES_*` 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 `PN` package does not include the above listed files.

### Post-Installation Scripts

To add a post-installation script to a package, add a `pkg_postinst_PACKAGENAME()` function to the `.bb` file and use `PACKAGENAME` as the name of the package you want to attach to the `postinst` script. Normally, `PN` can be used, which automatically expands to `PACKAGENAME`. A post-installation function has the following structure:

         pkg_postinst_PACKAGENAME () {
         #!/bin/sh -e
         # Commands to carry out
         }

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.

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:

         pkg_postinst_PACKAGENAME () {
         #!/bin/sh -e
         if [ x"$D" = "x" ]; then
              # Actions to carry out on the device go here
         else
              exit 1
         fi
         }

The previous example delays execution until the image boots again because the `D` variable 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.

## Adding a New Machine

Adding a new machine to the Yocto Project is a straightforward process. This section provides information that gives you an idea of the changes you must make. The information covers adding machines similar to those the Yocto Project already supports. Although well within the capabilities of the Yocto Project, adding a totally new architecture might require changes to `gcc/eglibc` and to the site information, which is beyond the scope of this manual.

For a complete example that shows how to add a new machine, see the "Creating a New BSP Layer Using the yocto-bsp Script" in the Yocto Project Board Support Package (BSP) Developer's Guide.

### Adding the Machine Configuration File

To add a machine configuration, you need to add a `.conf` file with details of the device being added to the `conf/machine/` file. The name of the file determines the name the OpenEmbedded build system uses to reference the new machine.

The most important variables to set in this file are as follows:

- `TARGET_ARCH` (e.g. "arm")

- `PREFERRED_PROVIDER_virtual/kernel` (see below)

- `MACHINE_FEATURES` (e.g. "apm screen wifi")

You might also need these variables:

- `SERIAL_CONSOLES` (e.g. "115200;ttyS0 115200;ttyS1")

- `KERNEL_IMAGETYPE` (e.g. "zImage")

- `IMAGE_FSTYPES` (e.g. "tar.gz jffs2")

You can find full details on these variables in the reference section. You can leverage many existing machine `.conf` files from `meta/conf/machine/`.

### Adding a Kernel for the Machine

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 recipe. You can find several kernel examples in the Source Directory at `meta/recipes-kernel/linux` that you can use as references.

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

If you are extending an existing kernel, it is usually a matter of adding a suitable defconfig file. The file needs to be added into a location similar to defconfig files used for other machines in a given kernel. A possible way to do this is by listing the file in the `SRC_URI` and adding the machine to the expression in `COMPATIBLE_MACHINE`:

         COMPATIBLE_MACHINE = '(qemux86|qemumips)'

### Adding a Formfactor Configuration File

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.

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

Following is an example for qemuarm:

         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

## Working With Libraries

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:

- How to include static library files

- How to use the Multilib feature to combine multiple versions of library files into a single image

- How to install multiple versions of the same library in parallel on the same system

### Including Static Library Files

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

The `PACKAGES` and `FILES_*` variables in the `meta/conf/bitbake.conf` configuration file define how files installed by the `do_install` task are packaged. By default, the `PACKAGES` variable contains `${PN}-staticdev`, which includes all static library files.

Some previously released versions of the Yocto Project defined the static library files through `${PN}-dev`.

Following, is part of the BitBake configuration file. You can see where the static library files are defined:

         PACKAGES = "${PN}-dbg ${PN} ${PN}-doc ${PN}-dev ${PN}-staticdev ${PN}-locale"
         PACKAGES_DYNAMIC = "${PN}-locale-*"
         FILES = ""

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

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

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

         FILES_${PN}-staticdev = "${libdir}/*.a ${base_libdir}/*.a"
         SECTION_${PN}-staticdev = "devel"
         RDEPENDS_${PN}-staticdev = "${PN}-dev (= ${EXTENDPKGV})"

### Combining Multiple Versions of Library Files into One Image

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."

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.

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 other different sets of libraries. The libraries could differ in architecture, compiler options, or other optimizations.

This section overviews the Multilib process only. For more details on how to implement Multilib, see the Multilib wiki page.

Aside from this wiki page, several examples exist in the `meta-skeleton` layer found in the Source Directory:

- `conf/multilib-example.conf` configuration file

- `conf/multilib-example2.conf` configuration file

- `recipes-multilib/images/core-image-multilib-example.bb` recipe

#### Preparing to Use Multilib

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

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 `meta/conf/multilib.conf` configuration file in the Source Directory to see how this is done using the `BBCLASSEXTEND` variable. Eventually, all recipes will be covered and this list will be unneeded.

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

#### Using Multilib

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 `local.conf` configuration file in the Build Directory. An example configuration would be as follows:

         MACHINE = "qemux86-64"
         require conf/multilib.conf
         MULTILIBS = "multilib:lib32"
         DEFAULTTUNE_virtclass-multilib-lib32 = "x86"
         IMAGE_INSTALL = "lib32-connman"

This example enables an additional library named `lib32` alongside the normal target packages. When combining these "lib32" alternatives, the example uses "x86" for tuning. For information on this particular tuning, see `meta/conf/machine/include/ia32/arch-ia32.inc`.

The example then includes `lib32-connman` 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:

         $ bitbake core-image-sato

You can also build Multilib packages specifically with a command like this:

         $  bitbake lib32-connman

#### Additional Implementation Details

Different packaging systems have different levels of native Multilib support. For the RPM Package Management System, the following implementation details exist:

- A unique architecture is defined for the Multilib packages, along with creating a unique deploy folder under `tmp/deploy/rpm` in the Build Directory. For example, consider `lib32` in a `qemux86-64` image. The possible architectures in the system are "all", "qemux86_64", "lib32_qemux86_64", and "lib32_x86".

- The `${MLPREFIX}` variable is stripped from `${PN}` during RPM packaging. The naming for a normal RPM package and a Multilib RPM package in a `qemux86-64` system resolves to something similar to `bash-4.1-r2.x86_64.rpm` and `bash-4.1.r2.lib32_x86.rpm`, respectively.

- When installing a Multilib image, the RPM backend first installs the base image and then installs the Multilib libraries.

- The build system relies on RPM to resolve the identical files in the two (or more) Multilib packages.

For the IPK Package Management System, the following implementation details exist:

- The `${MLPREFIX}` is not stripped from `${PN}` during IPK packaging. The naming for a normal RPM package and a Multilib IPK package in a `qemux86-64` system resolves to something like `bash_4.1-r2.x86_64.ipk` and `lib32-bash_4.1-rw_x86.ipk`, respectively.

- The IPK deploy folder is not modified with `${MLPREFIX}` because packages with and without the Multilib feature can exist in the same folder due to the `${PN}` differences.

- IPK defines a sanity check for Multilib installation using certain rules for file comparison, overridden, etc.

### Installing Multiple Versions of the Same Library

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.

The process is straight forward 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 `PN` 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. `clutter`), 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 `clutter` library to co-exist on the same system:

         clutter-1.6_1.6.20.bb
         clutter-1.8_1.8.4.bb

Additionally, if you have other recipes that depend on a given library, you need to use the `DEPENDS` 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 `clutter` library, use the following in your recipe:

         DEPENDS = "clutter-1.8"

## Creating Partitioned Images

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 () to create the properly partitioned image.

The `wic` command generates partitioned images from existing OpenEmbedded build artifacts. Image generation is driven by partitioning commands contained in an Openembedded kickstart file (`.wks`) specified either directly on the command-line or as one of a selection of canned `.wks` files (see 'wic list images'). 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.

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

### Background

This section provides some background on the `wic` utility. While none of this information is required to use `wic`, you might find it interesting.

- 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.

- `wic` is loosely based on the Meego Image Creator (`mic`) framework. The `wic` 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.

- `wic` 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 `directdisk.bbclass` and `mkefidisk.sh` script. The replaced scripts are implemented by a general-purpose partitioning language based on Red Hat kickstart syntax. Underlying code for `wic` succeeded from several projects over time.

### Requirements

In order to use the `wic` utility with the OpenEmbedded Build system, you need to meet the following requirements:

- The Linux distribution on your development host must support the Yocto Project. See the "Supported Linux Distributions" section in the Yocto Project Reference Manual for this list of distributions.

- The standard system utilities, such as `cp`, must be installed on your development host system.

- The GNU Parted package must be installed on your development host system.

- Have the build artifacts already available. You must already have created an image using the Openembedded build system (e.g. `core-image-minimal`. It might seem redundant to generate an image in order to create an image using `wic`, but the artifacts are needed and they are generated with the build system.

- You must have sourced one of the build environment setup scripts (i.e. `&OE_INIT_FILE;` or `oe-init-build-env-memres`) found in the Build Directory.

### Getting Help

You can get general help for the `wic` by entering the `wic` command by itself or by entering the command with a help argument as follows:

         $ wic -h
         $ wic --help

Currently, `wic` supports two commands: `create` and `list`. You can get help for these commands as follows:

         $ wic help <command>

You can find more out about the images `wic` creates using the provided kickstart files with the following form of the command:

         $ wic list <image> help

Where `<image>` is either `directdisk` or `mkefidisk`.

### Operational Modes

You can run `wic` in two modes: Raw and Cooked:

- Raw Mode: You explicitly specify build artifacts through command-line arguments.

- Cooked Mode: The current `MACHINE` setting and image name are used to automatically locate and provide the build artifacts.

#### Raw Mode

The general form of the 'wic' command in raw mode is:

         $ wic create <image_name>.wks -r <rootfs_dir> -b <bootimg_dir> /
               -k <kernel_dir> -n <native_sysroot>

You do not need root privileges to run `wic`. In fact, you should not run as root when using the utility.

Following is a description of the `wic` parameters and options:

- `<image_name>.wks`: An OpenEmbedded kickstart file. You can provide your own custom file or use a file from a set of provided files as described following this list.

- `-r <rootfs_dir>`: Specifies the path to the root filesystem directory to be used and the `.wks` root filesystem source.

- `-b <bootimg_dir>`: Specifies the path to the directory that contains the boot artifacts (e.g. the `EFI` or `syslinux` directories) to use as the `.wks` boot image source.

- `-k <kernel_dir>`: Specifies the path to the dir containing the kernel to use in the `.wks` boot image.

- `-n <native_sysroot>`: Specifies the path to the native sysroot that contains the tools used to build the image.

#### Cooked Mode

The general form of the `wic` command using Cooked Mode is:

         $ wic create <kickstart_file> -e <image_name>

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 `.wks` file or one provided with the release.

Following is a description of the `wic` parameters and options:

- `<kickstart>`: An OpenEmbedded kickstart file. You can provide your own custom file or supplied file.

- `-e <image_name>`: Specifies the image built using the OpenEmbedded build system.

### Using a Provided Kickstart File

If you do not want to create your own `.wks` file, you can use a provided file. Use the following command to list the available files:

         $ wic list images
         mkefidisk Create an EFI disk image
         directdisk Create a 'pcbios' direct disk image

When you use a provided file, you do not have to use the `.wks` extension. Here is an example in Raw Mode that uses the `directdisk` file:

         $ wic create directdisk -r <rootfs_dir> -b <bootimg_dir> \
               -k <kernel_dir> -n <native_sysroot>

Here are the actual partition language commands used in the `mkefidisk.wks` file to generate an image:

         # 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 --ondisk sda --fstype=efi --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"

### Examples

This section provides several examples that show how to use the `wic` utility. All the examples assume the list of requirements in the "Requirements" section have been met. The examples assume the previously generated image is `core-image-minimal`.

#### Generate an Image using a Provided Kickstart File

This example runs in Cooked Mode and uses the `mkefidisk` kickstart file:

         $ 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

This example shows the easiest way to create an image by running in Cooked Mode and using the `-e` option with a provided kickstart file. All that is necessary is to specify the image used to generate the artifacts. Your `local.conf` needs to have the `MACHINE` variable set to the machine you are using, which is "minnow" in this example.

The output specifies exactly which image was created as well as where it was created. The output also names the artifacts used and the exact `.wks` script that was used to generate the image.

You should always verify the details provided in the output to make sure that the image was indeed created exactly as expected.

Continuing with the example, you can now directly `dd` the image to a USB stick, or whatever media for which you built your image, and boot the resulting media:

         $ 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

#### Using a Modified Kickstart File

Because `wic` 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 `directdisk` kickstart file.

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

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

The example begins by making a copy of the `directdisk.wks` file in the `scripts/lib/image/canned-wks` directory and then changing the lines that specify the target disk from which to boot.

         $ 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

Next, the example modifies the `directdisksdb.wks` file and changes all instances of "`--ondisk sda`" to "`--ondisk sdb`". The example changes the following two lines and leaves the remaining lines untouched:

         part /boot --source bootimg --ondisk sdb --fstype=msdos --label boot --active --align 1024
         part / --source rootfs --ondisk sdb --fstype=ext3 --label platform --align 1024

Once the lines are changed, the example generates the `directdisksdb` image. The command points the process at the `core-image-minimal` artifacts for the Next Unit of Computing (nuc) `MACHINE` the `local.conf`.

         $ 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

Continuing with the example, you can now directly `dd` the image to a USB stick, or whatever media for which you built your image, and boot the resulting media:

         $ 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

#### Creating an Image Based on `core-image-minimal` and `crownbay-noemgd`

This example creates an image based on `core-image-minimal` and a `crownbay-noemgd` `MACHINE` that works right out of the box.

         $ 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

#### Using a Modified Kickstart File and Running in Raw Mode

This next example manually specifies each build artifact (runs in Raw Mode) and uses a modified kickstart file. The example also uses the `-o` option to cause `wic` to create the output somewhere other than the default `/var/tmp/wic` directory:

         $ 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

For this example, `MACHINE` did not have to be specified in the `local.conf` file since the artifact is manually specified.

### OpenEmbedded Kickstart (.wks) Reference

The current `wic` implementation supports only the basic kickstart partitioning commands: `partition` (or `part` for short) and `bootloader`.

Following is a listing of the commands, their syntax, and meanings. The commands are based on the Fedora kickstart documentation but with modifications to reflect `wic` capabilities.

         http://fedoraproject.org/wiki/Anaconda/Kickstart#part_or_partition
         http://fedoraproject.org/wiki/Anaconda/Kickstart#bootloader

#### Command: part or partition

This command creates a partition on the system and uses the following syntax:

         part <mntpoint>

The `<mntpoint>` is where the partition will be mounted and must be of one of the following forms:

- `/<path>`: For example, `/`, `/usr`, and `/home`

- `swap`: The partition will be used as swap space.

Following are the supported options:

- `--size`: 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 `--source`.

- `--source`: This option is a wic-specific option that can currently have one of two values, "bootimg" or "rootfs".

  If `--source rootfs` is used, it tells the `wic` command to create a partition as large as needed to fill with the contents of the root filesystem (specified by the `-r` `wic` option) and to fill it with the contents of `/rootfs`.

  If `--source bootimg` is used, it tells the `wic` command to create a partition as large as needed to fill with the contents of the boot partition (specified by the `-b` `wic` option). Exactly what those contents are depend on the value of the `--fstype` option for that partition. If `--fstype=efi` is specified, the boot artifacts contained in HDDDIR are used, and if `--fstype=msdos` is specified, the boot artifacts found in `STAGING_DATADIR` are used.

- `--ondisk` or `--ondrive`: Forces the partition to be created on a particular disk.

- `--fstype`: Sets the file system type for the partition. Valid values are:

  - `msdos`

  - `efi`

  - `ext4`

  - `ext3`

  - `ext2`

  - `btrfs`

  - `swap`

- `--label label`: 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.

- `--active`: Marks the partition as active.

- `--align (in KBytes)`: This option is specific to the Meego Image Creator (mic) that says to start a partition on an x KBytes boundary.

#### Command: bootloader

This command specifies how the boot loader should be and supports the following options:

- `--timeout`: Specifies the number of seconds before the bootloader times out and boots the default option.

- `--append`: Specifies kernel parameters. These will be added to the syslinux `APPEND` or `grub` kernel command line.

  The boot type is determined by the fstype of the `/boot` mountpoint. If the fstype is "msdos" the boot type is "pcbios", otherwise it is the fstype, which is currently "efi" (more to be added later).

  If the boot type is "efi", the image will use `grub` and has one menuentry: "boot".

  If the boot type is "pcbios", the image will use syslinux and has one menu label: "boot".

  Future updates will implement more options. If you use anything that is not specifically supported, results can be unpredictable.

## Configuring the Kernel

Configuring the Yocto Project kernel consists of making sure the `.config` file has all the right information in it for the image you are building. You can use the `menuconfig` tool and configuration fragments to make sure your `.config` file is just how you need it. This section describes how to use `menuconfig`, create and use configuration fragments, and how to interactively tweak your `.config` file to create the leanest kernel configuration file possible.

For more information on kernel configuration, see the "Changing the Configuration" section in the Yocto Project Linux Kernel Development Manual.

### Using `menuconfig`

The easiest way to define kernel configurations is to set them through the `menuconfig` tool. This tool provides an interactive method with which to set kernel configurations. For general information on `menuconfig`, see .

To use the `menuconfig` tool in the Yocto Project development environment, you must launch it using BitBake. Thus, the environment must be set up using the `&OE_INIT_FILE;` or `oe-init-build-env-memres` script found in the Build Directory. The following commands run `menuconfig` assuming the Source Directory top-level folder is `~/poky`:

         $ cd poky
         $ source oe-init-build-env
         $ bitbake linux-yocto -c menuconfig

Once `menuconfig` 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 `.config` configuration file.

Consider an example that configures the `linux-yocto-3.4` kernel. The OpenEmbedded build system recognizes this kernel as `linux-yocto`. Thus, the following commands from the shell in which you previously sourced the environment initialization script cleans the shared state cache and the `WORKDIR` directory and then runs `menuconfig`:

         $ bitbake linux-yocto -c menuconfig

Once `menuconfig` launches, use the interface to navigate through the selections to find the configuration settings in which you are interested. For example, consider the `CONFIG_SMP` configuration setting. You can find it at `Processor Type and Features` under the configuration selection `Symmetric Multi-processing Support`. 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.

Saving the selections updates the `.config` 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 `tmp/work/`. The actual `.config` 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 3.4 kernel and you were building a QEMU image targeted for `x86` architecture, the `.config` file would be located here:

         poky/build/tmp/work/qemux86-poky-linux/linux-yocto-3.4.11+git1+84f...
            ...656ed30-r1/linux-qemux86-standard-build

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 `linux-yocto-3.4...` might differ.

Within the `.config` file, you can see the kernel settings. For example, the following entry shows that symmetric multi-processor support is not set:

         # CONFIG_SMP is not set

A good method to isolate changed configurations is to use a combination of the `menuconfig` tool and simple shell commands. Before changing configurations with `menuconfig`, copy the existing `.config` and rename it to something else, use `menuconfig` to make as many changes an 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.

Be sure to make a copy of the `.config` and don't just rename it. The build system needs an existing `.config` from which to work.

### Creating Configuration Fragments

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 `.config` file, which is in the Build Directory in `tmp/work/<arch>-poky-linux/linux-yocto-<release-specific-string>/linux-<arch>-<build-type>`.

It is simple to create a configuration fragment. For example, issuing the following from the shell creates a configuration fragment file named `my_smp.cfg` that enables multi-processor support within the kernel:

         $ echo "CONFIG_SMP=y" >> my_smp.cfg

All configuration files must use the `.cfg` extension in order for the OpenEmbedded build system to recognize them as a configuration fragment.

Where do you put your configuration files? You can place these configuration files in the same area pointed to by `SRC_URI`. The OpenEmbedded build system will pick up the configuration and add it to the kernel's configuration. For example, suppose you had a set of configuration options in a file called `myconfig.cfg`. If you put that file inside a directory named `linux-yocto` that resides in the same directory as the kernel's append file and then add a `SRC_URI` 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.

         SRC_URI += "file://myconfig.cfg"

As mentioned earlier, you can group related configurations into multiple files and name them all in the `SRC_URI` 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 `SRC_URI` statement like the following in your append file:

         SRC_URI += "file://myconfig.cfg \
                file://eth.cfg \
                file://gfx.cfg"

### Fine-Tuning the Kernel Configuration File

You can make sure the `.config` 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.

As part of the kernel build process, the `kernel_configcheck` task runs. This task validates the kernel configuration by checking the final `.config` file against the input files. During the check, the task produces warning messages for the following issues:

- Requested options that did not make the final `.config` file.

- Configuration items that appear twice in the same configuration fragment.

- Configuration items tagged as "required" that were overridden.

- A board overrides a non-board specific option.

- Listed options not valid for the kernel being processed. In other words, the option does not appear anywhere.

The `kernel_configcheck` task can also optionally report if an option is overridden during processing.

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

To streamline the configuration, do the following:

1. Start with a full configuration that you know works - it builds and boots successfully. This configuration file will be your baseline.

2. Separately run the `configme` and `kernel_configcheck` tasks.

3. Take the resulting list of files from the `kernel_configcheck` task warnings and do the following:

   - Drop values that are redefined in the fragment but do not change the final `.config` file.

   - Analyze and potentially drop values from the `.config` file that override required configurations.

   - Analyze and potentially remove non-board specific options.

   - Remove repeated and invalid options.

4. After you have worked through the output of the kernel configuration audit, you can re-run the `configme` and `kernel_configcheck` tasks to see the results of your changes. If you have more issues, you can deal with them as described in the previous step.

Iteratively working through steps two through four eventually yields a minimal, streamlined configuration file. Once you have the best `.config`, you can build the Linux Yocto kernel.

## Patching the Kernel

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.

You can use the `yocto-kernel` script found in the Source Directory under `scripts` to manage kernel patches and configuration. See the "Managing kernel Patches and Config Items with yocto-kernel" section in the Yocto Project Board Support Packages (BSP) Developer's Guide for more information.

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

The example assumes a clean build exists for the `qemux86` machine in a Source Directory named `poky`. Furthermore, the Build Directory is `build` and is located in `poky` and the kernel is based on the Linux 3.4 kernel. For general information on how to configure the most efficient build, see the "Building an Image" section in the Yocto Project Quick Start.

Also, for more information on patching the kernel, see the "Applying Patches" section in the Yocto Project Linux Kernel Development Manual.

### Create a Layer for your Changes

The first step is to create a layer so you can isolate your changes:

         $ cd ~/poky
         $ mkdir meta-mylayer

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 "Understanding and Creating Layers" section.

### Finding the Kernel Source Code

Each time you build a kernel image, the kernel source code is fetched and unpacked into the following directory:

         ${S}/linux

See the "Finding the Temporary Source Code" section and the `S` variable for more information about where source is kept during a build.

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

### Creating the Patch

Two methods exist by which you can create the patch: Git workflow and Quilt workflow. For kernel patches, the Git workflow is more appropriate. This section assumes the Git workflow and shows the steps specific to this example.

1. Change the working directory: Change to where the kernel source code is before making your edits to the `calibrate.c` file:

            $ cd ~/poky/build/tmp/work/qemux86-poky-linux/linux-yocto-${PV}-${PR}/linux

   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.

   The `PV` and `PR` variables represent the version and revision for the `linux-yocto` recipe. The `PV` variable includes the Git meta and machine hashes, which make the directory name longer than you might expect.

2. Edit the source file: Edit the `init/calibrate.c` file to have the following changes:

            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)) {
                      .
                      .
                      .

3. Stage and commit your changes: These Git commands display the modified file, stage it, and then commit the file:

            $ git status
            $ git add init/calibrate.c
            $ git commit -m "calibrate: Add printk example"

4. Generate the patch file: This Git command creates the a patch file named `0001-calibrate-Add-printk-example.patch` in the current directory.

            $ git format-patch -1

### Set Up Your Layer for the Build

These steps get your layer set up for the build:

1. Create additional structure: Create the additional layer structure:

            $ cd ~/poky/meta-mylayer
            $ mkdir conf
            $ mkdir recipes-kernel
            $ mkdir recipes-kernel/linux
            $ mkdir recipes-kernel/linux/linux-yocto

   The `conf` directory holds your configuration files, while the `recipes-kernel` directory holds your append file and your patch file.

2. Create the layer configuration file: Move to the `meta-mylayer/conf` directory and create the `layer.conf` file as follows:

            # 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"

   Notice `mylayer` as part of the last three statements.

3. Create the kernel recipe append file: Move to the `meta-mylayer/recipes-kernel/linux` directory and create the `linux-yocto_3.4.bbappend` file as follows:

            FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"

            SRC_URI += "file://0001-calibrate-Add-printk-example.patch"

            PRINC := "${@int(PRINC) + 1}"

   The `FILESEXTRAPATHS` and `SRC_URI` statements enable the OpenEmbedded build system to find the patch file. For more information on using append files, see the "Using .bbappend Files" section.

4. Put the patch file in your layer: Move the `0001-calibrate-Add-printk-example.patch` file to the `meta-mylayer/recipes-kernel/linux/linux-yocto` directory.

### Set Up for the Build

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:

- Build for the correct target architecture: Your selected `MACHINE` definition within the `local.conf` file in the Build Directory specifies the target architecture used when building the Linux kernel. By default, `MACHINE` is set to `qemux86`, which specifies a 32-bit Intel Architecture target machine suitable for the QEMU emulator.

- Identify your `meta-mylayer` layer: The `BBLAYERS` variable in the `bblayers.conf` file found in the `poky/build/conf` directory needs to have the path to your local `meta-mylayer` layer. By default, the `BBLAYERS` variable contains paths to `meta`, `meta-yocto`, and `meta-yocto-bsp` in the `poky` Git repository. Add the path to your `meta-mylayer` location:

           BBLAYERS ?= " \
             $HOME/poky/meta \
             $HOME/poky/meta-yocto \
             $HOME/poky/meta-yocto-bsp \
             $HOME/poky/meta-mylayer \
             "

           BBLAYERS_NON_REMOVABLE ?= " \
             $HOME/poky/meta \
             $HOME/poky/meta-yocto \
             "

### Build the Modified QEMU Kernel Image

The following steps build your modified kernel image:

1. Be sure your build environment is initialized: Your environment should be set up since you previously sourced the `&OE_INIT_FILE;` script. If it is not, source the script again from `poky`.

            $ cd ~/poky
            $ source &OE_INIT_FILE;

2. Clean up: Be sure to clean the shared state out by running the `cleansstate` BitBake task as follows from your Build Directory:

            $ bitbake -c cleansstate linux-yocto

   Never remove any files by hand from the `tmp/deploy` directory inside the Build Directory. Always use the various BitBake clean tasks to clear out previous build artifacts.

3. Build the image: Next, build the kernel image using this command:

            $ bitbake -k linux-yocto

### Boot the Image and Verify Your Changes

These steps boot the image and allow you to see the changes

1. Boot the image: Boot the modified image in the QEMU emulator using this command:

            $ runqemu qemux86

2. Verify the changes: Log into the machine using `root` with no password and then use the following shell command to scroll through the console's boot output.

            # dmesg | less

   You should see the results of your `printk` statements as part of the output.

## Creating Your Own Distribution

When you build an image using the Yocto Project and do not alter any distribution Metadata, 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.

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:

- Create a layer for your new distro: 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 `local.conf` configuration file makes it easier to reproduce the same build configuration when using multiple build machines. See the "Creating a General Layer Using the yocto-layer Script" section for information on how to quickly set up a layer.

- Create the distribution configuration file: The distribution configuration file needs to be created in the `conf/distro` directory of your layer. You need to name it using your distribution name (e.g. `mydistro.conf`).

  The `DISTRO` variable in your `local.conf` file determines the name of your distribution.

  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 `conf/distro/include` 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.

  Your configuration file needs to set the following required variables:

           DISTRO_NAME [required]
           DISTRO_VERSION [required]

  These following variables are optional and you typically set them from the distribution configuration file:

           DISTRO_FEATURES [optional]
           DISTRO_EXTRA_RDEPENDS [optional]
           DISTRO_EXTRA_RRECOMMENDS [optional]
           TCLIBC [optional]

  If you want to base your distribution configuration file on the very basic configuration from OE-Core, you can use `conf/distro/defaultsetup.conf` as a reference and just include variables that differ as compared to `defaultsetup.conf`. Alternatively, you can create a distribution configuration file from scratch using the `defaultsetup.conf` file or configuration files from other distributions such as Poky or Angstrom as references.

- Provide miscellaneous variables: 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 `local.conf` file. The variables you use are not limited to the list in the previous bulleted item.

- Point to Your distribution configuration file: In your `local.conf` file in the Build Directory, set your `DISTRO` variable to point to your distribution's configuration file. For example, if your distribution's configuration file is named `mydistro.conf`, then you point to it as follows:

           DISTRO = "mydistro"

- Add more to the layer if necessary: Use your layer to hold other information needed for the distribution:

  - 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 a `.bbappend` for those. For general information and recommendations on how to add recipes to your layer, see the "Creating Your Own Layer" and "Best Practices to Follow When Creating Layers" sections.

  - Add any image recipes that are specific to your distribution.

  - Add a `psplash` append file for a branded splash screen. For information on append files, see the "Using .bbappend Files" section.

  - Add any other append files to make custom changes that are specific to individual recipes.

## Building a Tiny System

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.

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

### Overview

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:

- Determine your goals and guiding principles.

- Understand what contributes to your image size.

- Reduce the size of the root filesystem.

- Reduce the size of the kernel.

- Eliminate packaging requirements.

- Look for other ways to minimize size.

- Iterate on the process.

### Goals and Guiding Principles

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:

- 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).

- Find the areas that are currently taking 90% of the space and concentrate on reducing those areas.

- Do not create any difficult "hacks" to achieve your goals.

- Leverage the device-specific options.

- Work in a separate layer so that you keep changes isolated. For information on how to create layers, see the "Understanding and Creating Layers" section.

### Understand What Contributes to Your Image Size

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 `poky-tiny` distribution. Ultimately, you will want to make changes in your own distribution that are likely modeled after `poky-tiny`.

To use `poky-tiny` in your build, set the `DISTRO` variable in your `local.conf` file to "poky-tiny" as described in the "Creating Your Own Distribution" section.

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 `__init__` functions.

To help you see where you currently are with kernel and root filesystem sizes, you can use two tools found in the Source Directory in the `scripts/tiny/` directory:

- `ksize.py`: Reports component sizes for the kernel build objects.

- `dirsize.py`: Reports component sizes for the root filesystem.

This next tool and command helps you organize configuration fragments and view file dependencies in a human-readable form:

- `merge_config.sh`: 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.

  The `merge_config.sh` script is part of the Linux Yocto kernel Git repository in the `scripts/kconfig` directory.

  For more information on configuration fragments, see the "Generating Configuration Files" section of the Yocto Project Linux Kernel Development Manual and the "Creating Configuration Fragments" section, which is in this manual.

- `bitbake -u depexp -g <bitbake_target>`: 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.

### Trim the Root Filesystem

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 tweak the filesystem itself or select a different filesystem.

First, find out what is hogging your root filesystem by running the `dirsize.py` script from your root directory:

         $ cd <root-directory-of-image>
         $ dirsize.py 100000 > dirsize-100k.log
         $ cat dirsize-100k.log

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.

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:

         $ cd <image-directory>
         $ bitbake -u depexp -g <image>

Use the interface to select potential packages you wish to eliminate and see their dependency relationships.

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 `devtmpfs` and `mdev` instead of `udev`.

Use your `local.conf` file to make changes. For example, to eliminate `udev` and `glib`, set the following in the local configuration file:

         VIRTUAL-RUNTIME_dev_manager = ""

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

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

### Trim the Kernel

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?

You can modify the kernel source if you want to help with boot time.

Run the `ksize.py` script from the top-level Linux build directory to get an idea of what is making up the kernel:

         $ cd <top-level-linux-build-directory>
         $ ksize.py > ksize.log
         $ cat ksize.log

When you examine the log, you will see how much space is taken up with the built-in `.o` 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."

To examine, or drill down, into any particular area, use the `-d` option with the script:

         $ ksize.py -d > ksize.log

Using this option breaks out the individual file information for each area of the kernel (e.g. drivers, networking, and so forth).

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.

After figuring out what to eliminate, you need to reconfigure the kernel to reflect those changes during the next build. You could run `menuconfig` 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 `allnoconfig`, create configuration fragments for individual changes, and then manage the fragments into a single configuration file using `merge_config.sh`. The tool makes it easy for you to iterate using the configuration change and build cycle.

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.

### Remove Package Management Requirements

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.

To eliminate all the packaging requirements for an image, follow these steps:

1. Put the following line in your main recipe for the image to remove package management data files:

            ROOTFS_POSTPROCESS_COMMAND += "remove_packaging_data_files ;

   For example, the recipe for the `core-image-minimal` image contains this line. You can also add the line to the `local.conf` configuration file.

2. Be sure that "package-management" is not part of your `IMAGE_FEATURES` statement for the image. When you remove this feature, you are removing the package manager as well as its dependencies from the root filesystem.

### Look for Other Ways to Minimize Size

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:

- `eglibc`: In general, follow this process:

  1. Remove `eglibc` features from `DISTRO_FEATURES` that you think you do not need.

  2. Build your distribution.

  3. 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 `ncurses`. Or, if support for those characters is needed, determine what `eglibc` features provide the support and restore the configuration.

  4. Rebuild and repeat the process.

- `busybox`: For BusyBox, use a process similar as described for `eglibc`. 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.

### Iterate on the Process

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.

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.

## Working with Packages

This section describes a few tasks that involve packages:

- Excluding packages from an image

- Incrementing a package revision number

- Handling a package name alias

- Handling optional module packaging

- Using Runtime Package Management

- Setting up and running package test (ptest)

### Excluding Packages from an Image

You might find it necessary to prevent specific packages from being installed into an image. If so, you can use several variables to direct the build system to essentially ignore installing recommended packages or to not install a package at all.

The following list introduces variables you can use to prevent packages from being installed into your image. Each of these variables only works with IPK and RPM package types. Support for Debian packages does not exist. Also, you can use these variables from your `local.conf` file or attach them to a specific image recipe by using a recipe name override. For more detail on the variables, see the descriptions in the Yocto Project Reference Manual's glossary chapter.

- `BAD_RECOMMENDATIONS`: Use this variable to specify "recommended-only" packages that you do not want installed.

- `NO_RECOMMENDATIONS`: Use this variable to prevent all "recommended-only" packages from being installed.

- `PACKAGE_EXCLUDE`: Use this variable to prevent specific packages from being installed regardless of whether they are "recommended-only" or not. You need to realize that the build process could fail with an error when you prevent the installation of a package whose presence is required by an installed package.

### Incrementing a Package Revision Number

If a committed change results in changing the package output, then the value of the `PR` variable needs to be increased (or "bumped"). Increasing `PR` occurs one of two ways:

- Automatically using a Package Revision Service (PR Service).

- Manually incrementing the `PR` variable.

Given that one of the challenges any build system and its users face is how to maintain a package feed that is compatible with existing package manager applications such as RPM, APT, and OPKG, using an automated system is much preferred over a manual system. In either system, the main requirement is that version numbering increases in a linear fashion and that a number of version components exist that support that linear progression.

The following two sections provide information on the PR Service and on manual `PR` bumping.

#### Working With a PR Service

As mentioned, attempting to maintain revision numbers in the Metadata is error prone, inaccurate and causes problems for people submitting recipes. Conversely, the PR Service automatically generates increasing numbers, particularly the revision field, which removes the human element.

For additional information on using a PR Service, you can see the PR Service wiki page.

The Yocto Project uses variables in order of decreasing priority to facilitate revision numbering (i.e. `PE`, `PV`, and `PR` for epoch, version and revision, respectively). The values are highly dependent on the policies and procedures of a given distribution and package feed.

Because the OpenEmbedded build system uses "signatures", which are unique to a given build, the build system knows when to rebuild packages. All the inputs into a given task are represented by a signature, which can trigger a rebuild when different. Thus, the build system itself does not rely on the `PR` numbers to trigger a rebuild. The signatures, however, can be used to generate `PR` values.

The PR Service works with both `OEBasic` and `OEBasicHash` generators. The value of `PR` bumps when the checksum changes and the different generator mechanisms change signatures under different circumstances.

As implemented, the build system includes values from the PR Service into the `PR` field as an addition using the form "`.x`" so `r0` becomes `r0.1`, `r0.2` and so forth. This scheme allows existing `PR` values to be used for whatever reasons, which include manual `PR` bumps should it be necessary.

By default, the PR Service is not enabled or running. Thus, the packages generated are just "self consistent". The build system adds and removes packages and there are no guarantees about upgrade paths but images will be consistent and correct with the latest changes.

The simplest form for a PR Service is for it to exist for a single host development system that builds the package feed (building system). For this scenario, you can enable a local PR Service by setting `PRSERV_HOST` in your `local.conf` file in the Build Directory:

         PRSERV_HOST = "localhost:0"

Once the service is started, packages will automatically get increasing `PR` values and BitBake will take care of starting and stopping the server.

If you have a more complex setup where multiple host development systems work against a common, shared package feed, you have a single PR Service running and it is connected to each building system. For this scenario, you need to start the PR Service using the `bitbake-prserv` command:

         bitbake-prserv &dash;&dash;host <ip> &dash;&dash;port <port> &dash;&dash;start

In addition to hand-starting the service, you need to update the `local.conf` file of each building system as described earlier so each system points to the server and port.

It is also recommended you use Build History, which adds some sanity checks to package versions, in conjunction with the server that is running the PR Service. To enable build history, add the following to each building system's `local.conf` file:

         # It is recommended to activate "buildhistory" for testing the PR service
         INHERIT += "buildhistory"
         BUILDHISTORY_COMMIT = "1"

For information on Build History, see the "Maintaining Build Output Quality" section in the Yocto Project Reference Manual.

The OpenEmbedded build system does not maintain `PR` information as part of the shared state (sstate) packages. If you maintain an sstate feed, its expected that either all your building systems that contribute to the sstate feed use a shared PR Service, or you do not run a PR Service on any of your building systems. Having some systems use a PR Service while others do not leads to obvious problems.

For more information on shared state, see the "Shared State Cache" section in the Yocto Project Reference Manual.

#### Manually Bumping PR

The alternative to setting up a PR Service is to manually bump the `PR` variable.

If a committed change results in changing the package output, then the value of the PR variable needs to be increased (or "bumped") as part of that commit. For new recipes you should add the `PR` variable and set its initial value equal to "r0", which is the default. Even though the default value is "r0", the practice of adding it to a new recipe makes it harder to forget to bump the variable when you make changes to the recipe in future.

If you are sharing a common `.inc` file with multiple recipes, you can also use the `INC_PR` variable to ensure that the recipes sharing the `.inc` file are rebuilt when the `.inc` file itself is changed. The `.inc` file must set `INC_PR` (initially to "r0"), and all recipes referring to it should set `PR` to "$(INC_PR).0" initially, incrementing the last number when the recipe is changed. If the `.inc` file is changed then its `INC_PR` should be incremented.

When upgrading the version of a package, assuming the `PV` changes, the `PR` variable should be reset to "r0" (or "$(INC_PR).0" if you are using `INC_PR`).

Usually, version increases occur only to packages. However, if for some reason `PV` changes but does not increase, you can increase the `PE` variable (Package Epoch). The `PE` variable defaults to "0".

Version numbering strives to follow the Debian Version Field Policy Guidelines. These guidelines define how versions are compared and what "increasing" a version means.

### Handling a Package Name Alias

Sometimes a package name you are using might exist under an alias or as a similarly named package in a different distribution. The OpenEmbedded build system implements a `distro_check` task that automatically connects to major distributions and checks for these situations. If the package exists under a different name in a different distribution, you get a `distro_check` mismatch. You can resolve this problem by defining a per-distro recipe name alias using the `DISTRO_PN_ALIAS` variable.

Following is an example that shows how you specify the `DISTRO_PN_ALIAS` variable:

         DISTRO_PN_ALIAS_pn-PACKAGENAME = "distro1=package_name_alias1 \
                                           distro2=package_name_alias2 \
                                           distro3=package_name_alias3 \
                                           ..."

If you have more than one distribution alias, separate them with a space. Note that the build system currently automatically checks the Fedora, OpenSUSE, Debian, Ubuntu, and Mandriva distributions for source package recipes without having to specify them using the `DISTRO_PN_ALIAS` variable. For example, the following command generates a report that lists the Linux distributions that include the sources for each of the recipes.

         $ bitbake world -f -c distro_check

The results are stored in the `build/tmp/log/distro_check-${DATETIME}.results` file found in the Source Directory.

### Handling Optional Module Packaging

Many pieces of software split functionality into optional modules (or plug-ins) and the plug-ins that are built might depend on configuration options. To avoid having to duplicate the logic that determines what modules are available in your recipe or to avoid having to package each module by hand, the OpenEmbedded build system provides functionality to handle module packaging dynamically.

To handle optional module packaging, you need to do two things:

- Ensure the module packaging is actually done

- Ensure that any dependencies on optional modules from other recipes are satisfied by your recipe

#### Making Sure the Packaging is Done

To ensure the module packaging actually gets done, you use the `do_split_packages` function within the `populate_packages` Python function in your recipe. The `do_split_packages` function searches for a pattern of files or directories under a specified path and creates a package for each one it finds by appending to the `PACKAGES` variable and setting the appropriate values for `FILES_packagename`, `RDEPENDS_packagename`, `DESCRIPTION_packagename`, and so forth. Here is an example from the `lighttpd` recipe:

         python populate_packages_prepend () {
             lighttpd_libdir = d.expand('${libdir}')
             do_split_packages(d, lighttpd_libdir, '^mod_(.*)\.so$',
                              'lighttpd-module-%s', 'Lighttpd module for %s',
                               extra_depends='')
         }

The previous example specifies a number of things in the call to `do_split_packages`.

- A directory within the files installed by your recipe through `do_install` in which to search.

- A regular expression to match module files in that directory. In the example, note the parentheses () that mark the part of the expression from which the module name should be derived.

- A pattern to use for the package names.

- A description for each package.

- An empty string for `extra_depends`, which disables the default dependency on the main `lighttpd` package. Thus, if a file in `${libdir}` called `mod_alias.so` is found, a package called `lighttpd-module-alias` is created for it and the `DESCRIPTION` is set to "Lighttpd module for alias".

Often, packaging modules is as simple as the previous example. However, more advanced options exist that you can use within `do_split_packages` to modify its behavior. And, if you need to, you can add more logic by specifying a hook function that is called for each package. It is also perfectly acceptable to call `do_split_packages` multiple times if you have more than one set of modules to package.

For more examples that show how to use `do_split_packages`, see the `connman.inc` file in the `meta/recipes-connectivity/connman/` directory of the `poky` source repository. You can also find examples in `meta/classes/kernel.bbclass`.

Following is a reference that shows `do_split_packages` mandatory and optional arguments:

         Mandatory arguments

         root
            The path in which to search
         file_regex
            Regular expression to match searched files.
            Use parentheses () to mark the part of this
            expression that should be used to derive the
            module name (to be substituted where %s is
            used in other function arguments as noted below)
         output_pattern
            Pattern to use for the package names. Must
            include %s.
         description
            Description to set for each package. Must
            include %s.

         Optional arguments

         postinst
            Postinstall script to use for all packages
            (as a string)
         recursive
            True to perform a recursive search - default
            False
         hook
            A hook function to be called for every match.
            The function will be called with the following
            arguments (in the order listed):

            f
               Full path to the file/directory match
            pkg
               The package name
            file_regex
               As above
            output_pattern
               As above
            modulename
               The module name derived using file_regex

         extra_depends
            Extra runtime dependencies (RDEPENDS) to be
            set for all packages. The default value of None
            causes a dependency on the main package
            (${PN}) - if you do not want this, pass empty
            string '' for this parameter.
         aux_files_pattern
            Extra item(s) to be added to FILES for each
            package. Can be a single string item or a list
            of strings for multiple items. Must include %s.
         postrm
            postrm script to use for all packages (as a
            string)
         allow_dirs
            True to allow directories to be matched -
            default False
         prepend
            If True, prepend created packages to PACKAGES
            instead of the default False which appends them
         match_path
            match file_regex on the whole relative path to
            the root rather than just the file name
         aux_files_pattern_verbatim
            Extra item(s) to be added to FILES for each
            package, using the actual derived module name
            rather than converting it to something legal
            for a package name. Can be a single string item
            or a list of strings for multiple items. Must
            include %s.
         allow_links
            True to allow symlinks to be matched - default
            False

#### Satisfying Dependencies

The second part for handling optional module packaging is to ensure that any dependencies on optional modules from other recipes are satisfied by your recipe. You can be sure these dependencies are satisfied by using the `PACKAGES_DYNAMIC` variable. Here is an example that continues with the `lighttpd` recipe shown earlier:

         PACKAGES_DYNAMIC = "lighttpd-module-.*"

The name specified in the regular expression can of course be anything. In this example, it is `lighttpd-module-` and is specified as the prefix to ensure that any `RDEPENDS` and `RRECOMMENDS` on a package name starting with the prefix are satisfied during build time. If you are using `do_split_packages` as described in the previous section, the value you put in `PACKAGES_DYNAMIC` should correspond to the name pattern specified in the call to `do_split_packages`.

### Using Runtime Package Management

During a build, BitBake always transforms a recipe into one or more packages. For example, BitBake takes the `bash` recipe and currently produces the `bash-dbg`, `bash-staticdev`, `bash-dev`, `bash-doc`, `bash-locale`, and `bash` packages. Not all generated packages are included in an image.

In several situations, you might need to update, add, remove, or query the packages on a target device at runtime (i.e. without having to generate a new image). Examples of such situations include:

- You want to provide in-the-field updates to deployed devices (e.g. security updates).

- You want to have a fast turn-around development cycle for one or more applications that run on your device.

- You want to temporarily install the "debug" packages of various applications on your device so that debugging can be greatly improved by allowing access to symbols and source debugging.

- You want to deploy a more minimal package selection of your device but allow in-the-field updates to add a larger selection for customization.

In all these situations, you have something similar to a more traditional Linux distribution in that in-field devices are able to receive pre-compiled packages from a server for installation or update. Being able to install these packages on a running, in-field device is what is termed "runtime package management".

In order to use runtime package management, you need a host/server machine that serves up the pre-compiled packages plus the required metadata. You also need package manipulation tools on the target. The build machine is a likely candidate to act as the server. However, that machine does not necessarily have to be the package server. The build machine could push its artifacts to another machine that acts as the server (e.g. Internet-facing).

A simple build that targets just one device produces more than one package database. In other words, the packages produced by a build are separated out into a couple of different package groupings based on criteria such as the target's CPU architecture, the target board, or the C library used on the target. For example, a build targeting the `qemuarm` device produces the following three package databases: `all`, `armv5te`, and `qemuarm`. If you wanted your `qemuarm` device to be aware of all the packages that were available to it, you would need to point it to each of these databases individually. In a similar way, a traditional Linux distribution usually is configured to be aware of a number of software repositories from which it retrieves packages.

Using runtime package management is completely optional and not required for a successful build or deployment in any way. But if you want to make use of runtime package management, you need to do a couple things above and beyond the basics. The remainder of this section describes what you need to do.

#### Build Considerations

This section describes build considerations that you need to be aware of in order to provide support for runtime package management.

When BitBake generates packages it needs to know what format(s) to use. In your configuration, you use the `PACKAGE_CLASSES` variable to specify the format.

You can choose to have more than one format but you must provide at least one.

If you would like your image to start off with a basic package database of the packages in your current build as well as have the relevant tools available on the target for runtime package management, you can include "package-management" in the `IMAGE_FEATURES` variable. Including "package-management" in this configuration variable ensures that when the image is assembled for your target, the image includes the currently-known package databases as well as the target-specific tools required for runtime package management to be performed on the target. However, this is not strictly necessary. You could start your image off without any databases but only include the required on-target package tool(s). As an example, you could include "opkg" in your `IMAGE_INSTALL` variable if you are using the IPK package format. You can then initialize your target's package database(s) later once your image is up and running.

Whenever you perform any sort of build step that can potentially generate a package or modify an existing package, it is always a good idea to re-generate the package index with:

        $ bitbake package-index

Realize that it is not sufficient to simply do the following:

        $ bitbake <some-package> package-index

This is because BitBake does not properly schedule the `package-index` target fully after any other target has completed. Thus, be sure to run the package update step separately.

As described below in the "Using IPK" section, if you are using IPK as your package format, you can make use of the `distro-feed-configs` recipe provided by `meta-oe` in order to configure your target to use your IPK databases.

When your build is complete, your packages reside in the `${TMPDIR}/deploy/<package-format>` directory. For example, if `${TMPDIR}` is `tmp` and your selected package type is IPK, then your IPK packages are available in `tmp/deploy/ipk`.

#### Host or Server Machine Setup

Typically, packages are served from a server using HTTP. However, other protocols are possible. If you want to use HTTP, then setup and configure a web server, such as Apache 2 or lighttpd, on the machine serving the packages.

As previously mentioned, the build machine can act as the package server. In the following sections that describe server machine setups, the build machine is assumed to also be the server.

##### Serving Packages via Apache 2

This example assumes you are using the Apache 2 server:

1. Add the directory to your Apache configuration, which you can find at `/etc/httpd/conf/httpd.conf`. Use commands similar to these on the development system. These example commands assume a top-level Source Directory named `poky` in your home directory. The example also assumes an RPM package type. If you are using a different package type, such as IPK, use "ipk" in the pathnames:

            <VirtualHost *:80>
              ....
                Alias /rpm ~/poky/build/tmp/deploy/rpm
                <Directory "~/poky/build/tmp/deploy/rpm">
                  Options +Indexes
                </Directory>
            </VirtualHost>

2. Reload the Apache configuration as described in this step. For all commands, be sure you have root privileges.

   If your development system is using Fedora or CentOS, use the following:

            # service httpd reload

   For Ubuntu and Debian, use the following:

            # /etc/init.d/apache2 reload

   For OpenSUSE, use the following:

            # /etc/init.d/apache2 reload

3. If you are using Security-Enhanced Linux (SELinux), you need to label the files as being accessible through Apache. Use the following command from the development host. This example assumes RPM package types:

            # chcon -R -h -t httpd_sys_content_t tmp/deploy/rpm

##### Serving Packages via lighttpd

If you are using lighttpd, all you need to do is to provide a link from your `${TMPDIR}/deploy/<package-format>` directory to lighttpd's document-root. You can determine the specifics of your lighttpd installation by looking through its configuration file, which is usually found at: `/etc/lighttpd/lighttpd.conf`.

For example, if you are using IPK, lighttpd's document-root is set to `/var/www/lighttpd`, and you had packages for a target named "BOARD", then you might create a link from your build location to lighttpd's document-root as follows:

        # ln -s $(PWD)/tmp/deploy/ipk /var/www/lighttpd/BOARD-dir

At this point, you need to start the lighttpd server. The method used to start the server varies by distribution. However, one basic method that starts it by hand is:

        # lighttpd -f /etc/lighttpd/lighttpd.conf

#### Target Setup

Setting up the target differs depending on the package management system. This section provides information for RPM and IPK.

##### Using RPM

The application for performing runtime package management of RPM packages on the target is called `smart`.

On the target machine, you need to inform `smart` of every package database you want to use. As an example, suppose your target device can use the following three package databases from a server named `server.name`: `all`, `i586`, and `qemux86`. Given this example, issue the following commands on the target:

         # smart channel --add all type=rpm-md baseurl=http://server.name/rpm/all
         # smart channel --add i585 type=rpm-md baseurl=http://server.name/rpm/i586
         # smart channel --add qemux86 type=rpm-md baseurl=http://server.name/rpm/qemux86

Also from the target machine, fetch the repository information using this command:

         # smart update

You can now use the `smart query` and `smart install` commands to find and install packages from the repositories.

##### Using IPK

The application for performing runtime package management of IPK packages on the target is called `opkg`.

In order to inform `opkg` of the package databases you want to use, simply create one or more `*.conf` files in the `/etc/opkg` directory on the target. The `opkg` application uses them to find its available package databases. As an example, suppose you configured your HTTP server on your machine named `www.mysite.com` to serve files from a `BOARD-dir` directory under its document-root. In this case, you might create a configuration file on the target called `/etc/opkg/base-feeds.conf` that contains:

         src/gz all http://www.mysite.com/BOARD-dir/all
         src/gz armv7a http://www.mysite.com/BOARD-dir/armv7a
         src/gz beagleboard http://www.mysite.com/BOARD-dir/beagleboard

As a way of making it easier to generate and make these IPK configuration files available on your target, simply define `FEED_DEPLOYDIR_BASE_URI` to point to your server and the location within the document-root which contains the databases. For example: if you are serving your packages over HTTP, your server's IP address is 192.168.7.1, and your databases are located in a directory called `BOARD-dir` underneath your HTTP server's document-root, you need to set `FEED_DEPLOYDIR_BASE_URI` to `http://192.168.7.1/BOARD-dir` and a set of configuration files will be generated for you in your target to work with this feed.

On the target machine, fetch (or refresh) the repository information using this command:

         # opkg update

You can now use the `opkg list` and `opkg install` commands to find and install packages from the repositories.

### Testing Packages With ptest

A Package Test (ptest) runs tests against packages built by the OpenEmbedded build system on the target machine. A ptest contains at least two items: the actual test, and a shell script (`run-ptest`) that starts the test. The shell script that starts the test must not contain the actual test, the script only starts it. On the other hand, the test can be anything from a simple shell script that runs a binary and checks the output to an elaborate system of test binaries and data files.

The test generates output in the format used by Automake:

         <result>: <testname>

where the result can be `PASS`, `FAIL`, or `SKIP`, and the testname can be any identifying string.

A recipe is "ptest-enabled" if it inherits ptest.

#### Adding ptest to Your Build

To add package testing to your build, add the `DISTRO_FEATURES` and `EXTRA_IMAGE_FEATURES` variables to your `local.conf` file, which is found in the Build Directory:

         DISTRO_FEATURES_append = " ptest"
         EXTRA_IMAGE_FEATURES += "ptest-pkgs"

Once your build is complete, the ptest files are installed into the `/usr/lib/<package>/ptest` directory within the image, where `<package>` is the name of the package.

#### Running ptest

The `ptest-runner` package installs a shell script that loops through all installed ptest test suites and runs them in sequence. Consequently, you might want to add this package to your image.

#### Getting Your Package Ready

In order to enable a recipe to run installed ptests on target hardware, you need to prepare the recipes that build the packages you want to test. Here is what you have to do for each recipe:

- Be sure the recipe inherits ptest: Include the following line in each recipe:

           inherit ptest

- Create `run-ptest`: This script starts your test. Locate the script where you will refer to it using `SRC_URI`. Here is an example that starts a test for `dbus`:

           #!/bin/sh
           cd test
           make -k runtest-TESTS

- Ensure dependencies are met: If the test adds build or runtime dependencies that normally do not exist for the package (such as requiring "make" to run the test suite), use the `DEPENDS` and `RDEPENDS` variables in your recipe in order for the package to meet the dependencies. Here is an example where the package has a runtime dependency on "make":

           RDEPENDS_${PN}-ptest += "make"

- Add a function to build the test suite: Not many packages support cross-compilation of their test suites. Consequently, you usually need to add a cross-compilation function to the package.

  Many packages based on Automake compile and run the test suite by using a single command such as `make check`. However, the native `make check` builds and runs on the same computer, while cross-compiling requires that the package is built on the host but executed on the target. The built version of Automake that ships with the Yocto Project includes a patch that separates building and execution. Consequently, packages that use the unaltered, patched version of `make check` automatically cross-compiles.

  However, you still must add a `do_compile_ptest` function to build the test suite. Add a function similar to the following to your recipe:

           do_compile_ptest() {
              oe_runmake buildtest-TESTS
           }

- Ensure special configurations are set: If the package requires special configurations prior to compiling the test code, you must insert a `do_configure_ptest` function into the recipe.

- Install the test suite: The `ptest.bbclass` class automatically copies the file `run-ptest` to the target and then runs make `install-ptest` to run the tests. If this is not enough, you need to create a `do_install_ptest` function and make sure it gets called after the "make install-ptest" completes.

## Building Software from an External Source

By default, the OpenEmbedded build system uses the Build Directory to build source code. The build process involves fetching the source files, unpacking them, and then patching them if necessary before the build takes place.

Situations exist where you might want to build software from source files that are external to and thus outside of the OpenEmbedded build system. For example, suppose you have a project that includes a new BSP with a heavily customized kernel. And, you want to minimize exposing the build system to the development team so that they can focus on their project and maintain everyone's workflow as much as possible. In this case, you want a kernel source directory on the development machine where the development occurs. You want the recipe's `SRC_URI` variable to point to the external directory and use it as is, not copy it.

To build from software that comes from an external source, all you need to do is inherit `externalsrc.bbclass` and then set the `EXTERNALSRC` variable to point to your external source code. Here are the statements to put in your `local.conf` file:

         INHERIT += "externalsrc"
         EXTERNALSRC_pn-myrecipe = "/some/path/to/your/source/tree"

By default, `externalsrc.bbclass` builds the source code in a directory separate from the external source directory as specified by `EXTERNALSRC`. If you need to have the source built in the same directory in which it resides, or some other nominated directory, you can set `EXTERNALSRC_BUILD` to point to that directory:

         EXTERNALSRC_BUILD_pn-myrecipe = "/path/to/my/source/tree"

## Selecting an Initialization Manager

By default, the Yocto Project uses `SysVinit` as the initialization manager. However, support also exists for `systemd`, which is a full replacement for `init` with parallel starting of services, reduced shell overhead and other features that are used by many distributions.

If you want to use `sysvinit`, you do not have to do anything. But, if you want to use `systemd`, you must take some steps as described in the following sections.

### Using systemd Exclusively

Set the following variables in your distribution configuration file as follows:

         DISTRO_FEATURES_append = " systemd"
         VIRTUAL-RUNTIME_init_manager = "systemd"

You can also prevent the `sysvinit` distribution feature from being automatically enabled as follows:

         DISTRO_FEATURES_BACKFILL_CONSIDERED = "sysvinit"

Doing so removes any redundant `sysvinit` scripts.

For information on the backfill variable, see `DISTRO_FEATURES_BACKFILL_CONSIDERED` in the Yocto Project Reference Manual.

### Using systemd for the Main Image and Using SysVinit for the Rescue Image

Set the following variables in your distribution configuration file as follows:

         DISTRO_FEATURES_append = " systemd"
         VIRTUAL-RUNTIME_init_manager = "systemd"

Doing so causes your main image to use the `packagegroup-core-boot.bb` recipe and `systemd`. The rescue/minimal image cannot use this package group. However, it can install `sysvinit` and the appropriate packages will have support for both `systemd` and `sysvinit`.

## Excluding Recipes From the Build

You might find that there are groups of recipes or append files that you want to filter out of the build process. Usually, this is not necessary. However, on rare occasions where you might want to use a layer but exclude parts that are causing problems, such as introducing a different version of a recipe, you can use `BBMASK` to exclude the recipe.

It is possible to filter or mask out `.bb` and `.bbappend` files. You can do this by providing an expression with the `BBMASK` variable. Here is one example:

         BBMASK = "/meta-mymachine/recipes-maybe/"

Here, all `.bb` and `.bbappend` files in the directory that match the expression are ignored during the build process.

The value you provide is passed to Python's regular expression compiler. The expression is compared against the full paths to the files. For complete syntax information, see Python's documentation at .

## Using an External SCM

If you're working on a recipe that pulls from an external Source Code Manager (SCM), it is possible to have the OpenEmbedded build system notice new recipe changes added to the SCM and then build the resulting package that depends on the new recipes by using the latest versions. This only works for SCMs from which it is possible to get a sensible revision number for changes. Currently, you can do this with Apache Subversion (SVN), Git, and Bazaar (BZR) repositories.

To enable this behavior, simply add the following to the `local.conf` configuration file found in the Build Directory:

         SRCREV_pn-<PN> = "${AUTOREV}"

where `PN` is the name of the recipe for which you want to enable automatic source revision updating.

In fact, the Yocto Project provides a distribution named `poky-bleeding`, whose configuration file contains the line:

         require conf/distro/include/poky-floating-revisions.inc

This line pulls in the listed include file that contains numerous lines of exactly that form:

         SRCREV_pn-gconf-dbus ?= "${AUTOREV}"
         SRCREV_pn-matchbox-common ?= "${AUTOREV}"
         SRCREV_pn-matchbox-config-gtk ?= "${AUTOREV}"
         SRCREV_pn-matchbox-desktop ?= "${AUTOREV}"
         SRCREV_pn-matchbox-keyboard ?= "${AUTOREV}"
         SRCREV_pn-matchbox-panel ?= "${AUTOREV}"
         SRCREV_pn-matchbox-panel-2 ?= "${AUTOREV}"
         SRCREV_pn-matchbox-themes-extra ?= "${AUTOREV}"
         SRCREV_pn-matchbox-terminal ?= "${AUTOREV}"
         SRCREV_pn-matchbox-wm ?= "${AUTOREV}"
         SRCREV_pn-matchbox-wm-2 ?= "${AUTOREV}"
         SRCREV_pn-settings-daemon ?= "${AUTOREV}"
         SRCREV_pn-screenshot ?= "${AUTOREV}"
         SRCREV_pn-libfakekey ?= "${AUTOREV}"
         SRCREV_pn-oprofileui ?= "${AUTOREV}"
              .
              .
              .

These lines allow you to experiment with building a distribution that tracks the latest development source for numerous packages.

### Caution

The `poky-bleeding` distribution is not tested on a regular basis. Keep this in mind if you use it.

## Creating a Read-Only Root Filesystem

Suppose, for security reasons, you need to disable your target device's root filesystem's write permissions (i.e. you need a read-only root filesystem). Or, perhaps you are running the device's operating system from a read-only storage device. For either case, you can customize your image for that behavior.

Supporting a read-only root filesystem requires that the system and applications do not try to write to the root filesystem. You must configure all parts of the target system to write elsewhere, or to gracefully fail in the event of attempting to write to the root filesystem.

### Creating the Root Filesystem

To create the read-only root filesystem, simply add the `read-only-rootfs` feature to your image. Using either of the following statements in your image recipe or from within the `local.conf` file found in the Build Directory causes the build system to create a read-only root filesystem:

         IMAGE_FEATURES = "read-only-rootfs"

or

         EXTRA_IMAGE_FEATURES += "read-only-rootfs"

For more information on how to use these variables, see the "Customizing Images Using Custom `IMAGE_FEATURES` and `EXTRA_IMAGE_FEATURES`" section. For information on the variables, see `IMAGE_FEATURES` and `EXTRA_IMAGE_FEATURES`.

### Post-Installation Scripts

It is very important that you make sure all post-Installation (`pkg_postinst`) scripts for packages that are installed into the image can be run at the time when the root filesystem is created during the build on the host system. These scripts cannot attempt to run during first-boot on the target device. With the `read-only-rootfs` feature enabled, the build system checks during root filesystem creation to make sure all post-installation scripts succeed. If any of these scripts still need to be run after the root filesystem is created, the build immediately fails. These checks during build time ensure that the build fails rather than the target device fails later during its initial boot operation.

Most of the common post-installation scripts generated by the build system for the out-of-the-box Yocto Project are engineered so that they can run during root filesystem creation (e.g. post-installation scripts for caching fonts). However, if you create and add custom scripts, you need to be sure they can be run during file system creation.

Here are some common problems that prevent post-installation scripts from running during root filesystem creation:

- Not using $D in front of absolute paths: The build system defines `$` `D` at root filesystem creation time, and it is blank when run on the target device. This implies two purposes for `$D`: ensuring paths are valid in both the host and target environments, and checking to determine which environment is being used as a method for taking appropriate actions.

- Attempting to run processes that are specific to or dependent on the target architecture: You can work around these attempts by using native tools to accomplish the same tasks, or by alternatively running the processes under QEMU, which has the `qemu_run_binary` function. For more information, see the `meta/classes/qemu.bbclass` class in the Source Directory.

### Areas With Write Access

With the `read-only-rootfs` feature enabled, any attempt by the target to write to the root filesystem at runtime fails. Consequently, you must make sure that you configure processes and applications that attempt these types of writes do so to directories with write access (e.g. `/tmp` or `/var/run`).

## Performing Automated Runtime Testing

The OpenEmbedded build system makes available a series of automated tests for images to verify runtime functionality.

Currently, there is only support for running these tests under QEMU.

These tests are written in Python making use of the `unittest` module, and the majority of them run commands on the target system over `ssh`. This section describes how you set up the environment to use these tests, run available tests, and write and add your own tests.

### Enabling Tests

In order to run tests, you need to do the following:

- Set up to avoid interaction with `sudo` for networking: To accomplish this, you must do one of the following:

  - Add `NOPASSWD` for your user in `/etc/sudoers` either for ALL commands or just for `runqemu-ifup`. You must provide the full path as that can change if you are using multiple clones of the source repository.

    On some distributions, you also need to comment out "Defaults requiretty" in `/etc/sudoers`.

  - Manually configure a tap interface for your system.

  - Run as root the script in `scripts/runqemu-gen-tapdevs`, which should generate a list of tap devices. This is the option typically chosen for Autobuilder-type environments.

- Set the `DISPLAY` variable: You need to set this variable so that you have an X server available (e.g. start `vncserver` for a headless machine).

- Be sure your host's firewall accepts incoming connections from 192.168.7.0/24: Some of the tests (in particular smart tests) start a HTTP server on a random high number port, which is used to serve files to the target. The smart module serves `${DEPLOY_DIR}/rpm` so it can run smart channel commands. That means your host's firewall must accept incoming connections from 192.168.7.0/24, which is the default IP range used for tap devices by `runqemu`.

Regardless of how you initiate the tests, if you built your image using `rm_work`, most of the tests will fail with errors because they rely on `${WORKDIR}/installed_pkgs.txt`.

### Running Tests

You can start the tests automatically or manually:

- Automatically Running Tests: To run the tests automatically after the OpenEmbedded build system successfully creates an image, first set the `TEST_IMAGE` variable to "1" in your `local.conf` file in the Build Directory:

           TEST_IMAGE = "1"

  Next, simply build your image. If the image successfully builds, the tests will be run:

           bitbake core-image-sato

- Manually Running Tests: To manually run the tests, first globally inherit `testimage.class` by editing your `local.conf` file:

          INHERIT += "testimage"

  Next, use BitBake to run the tests:

           bitbake -c testimage <image>

Regardless of how you run the tests, once they start, the following happens:

- A copy of the root filesystem is written to `${WORKDIR}/testimage`.

- The image is booted under QEMU using the standard `runqemu` script.

- A default timeout of 500 seconds occurs to allow for the boot process to reach the login prompt. You can change the timeout period by setting `TEST_QEMUBOOT_TIMEOUT` in the `local.conf` file.

- Once the boot process is reached and the login prompt appears, the tests run. The full boot log is written to `${WORKDIR}/testimage/qemu_boot_log`.

- Each test module loads in the order found in `TEST_SUITES`. You can find the full output of the commands run over `ssh` in `${WORKDIR}/testimgage/ssh_target_log`.

- If no failures occur, the task running the tests ends successfully. You can find the output from the `unittest` in the task log at `${WORKDIR}/temp/log.do_testimage`.

All test files reside in `meta/lib/oeqa/runtime` in the Source Directory. A test name maps directly to a Python module. Each test module may contain a number of individual tests. Tests are usually grouped together by the area tested (e.g tests for `systemd` reside in `meta/lib/oeqa/runtime/systemd.py`).

You can add tests to any layer provided you place them in the proper area and you extend `BBPATH` in the `local.conf` file as normal. Be sure that tests reside in `<layer>/lib/oeqa/runtime`.

Be sure that module names do not collide with module names used in the default set of test modules in `meta/lib/oeqa/runtime`.

You can change the set of tests run by appending or overriding `TEST_SUITES` variable in `local.conf`. Each name in `TEST_SUITES` represents a required test for the image. Test modules named within `TEST_SUITES` cannot be skipped even if a test is not suitable for an image (e.g. running the rpm tests on an image without `rpm`). Appending "auto" to `TEST_SUITES` causes the build system to try to run all tests that are suitable for the image (i.e. each test module may elect to skip itself).

The order you list tests in `TEST_SUITES` is important. The order influences test dependencies. Consequently, tests that depend on other tests should be added after the test on which they depend. For example, since `ssh` depends on the `ping` test, `ssh` needs to come after `ping` in the list. The test class provides no re-ordering or dependency handling.

Each module can have multiple classes with multiple test methods. And, Python `unittest` rules apply.

Here are some things to keep in mind when running tests:

- The default tests for the image are defined as:

           DEFAULT_TEST_SUITES_pn-<image> = "ping ssh df connman syslog xorg scp vnc date rpm smart dmesg"

- Add your own test to the list of the by using the following:

           TEST_SUITES_append = " mytest"

- Run a specific list of tests as follows:

           TEST_SUITES = "test1 test2 test3"

  Remember, order is important. Be sure to place a test that is dependent on another test later in the order.

### Writing New Tests

As mentioned previously, all new test files need to be in the proper place for the build system to find them. New tests for additional functionality outside of the core should be added to the layer that adds the functionality, in `<layer>/lib/oeqa/runtime` (as long as `BBPATH` is extended in the layer's `layer.conf` file as normal). Just remember that filenames need to map directly to test (module) names and that you do not use module names that collide with existing core tests.

To create a new test, start by copying an existing module (e.g. `syslog.py` or `gcc.py` are good ones to use). Test modules can use code from `meta/lib/oeqa/utils`, which are helper classes.

Structure shell commands such that you rely on them and they return a single code for success. Be aware that sometimes you will need to parse the output. See the `df.py` and `date.py` modules for examples.

You will notice that all test classes inherit `oeRuntimeTest`, which is found in `meta/lib/oetest.py`. This base class offers some helper attributes, which are described in the following sections:

#### Class Methods

Class methods are as follows:

- `hasPackage(pkg)`: Returns "True" if `pkg` is in the installed package list of the image, which is based on `${WORKDIR}/installed_pkgs.txt` that is generated during the `do.rootfs` task.

- `hasFeature(feature)`: Returns "True" if the feature is in `IMAGE_FEATURES` or `DISTRO_FEATURES`.

- `restartTarget(params)`: Restarts the QEMU image optionally passing `params` to the `runqemu` script's `qemuparams` list (e.g "-m 1024" for more memory).

#### Class Attributes

Class attributes are as follows:

- `pscmd`: Equals "ps -ef" if `procps` is installed in the image. Otherwise, `pscmd` equals "ps" (busybox).

- `tc`: The called text context, which gives access to the following attributes:

  - `d`: The BitBake data store, which allows you to use stuff such as `oeRuntimeTest.tc.d.getVar("VIRTUAL-RUNTIME_init_manager")`.

  - `testslist` and `testsrequired`: Used internally. The tests do not need these.

  - `filesdir`: The absolute path to `meta/lib/oeqa/runtime/files`, which contains helper files for tests meant for copying on the target such as small files written in C for compilation.

  - `qemu`: Provides access to the `QemuRunner` object, which is the class that boots the image. The `qemu` attribute provides the following useful attributes:

    - `ip`: The machine's IP address.

    - `host_ip`: The host IP address, which is only used by smart tests.

  - `target`: The `SSHControl` object, which is used for running the following commands on the image:

    - `host`: Used internally. The tests do not use this command.

    - `timeout`: A global timeout for commands run on the target for the instance of a test. The default is 300 seconds.

    - `run(cmd, timeout=None)`: The single, most used method. This command is a wrapper for: `ssh root@host "cmd"`. The command returns a tuple: (status, output), which are what their names imply - the return code of 'cmd' and whatever output it produces. The optional timeout argument represents the number of seconds the test should wait for 'cmd' to return. If the argument is "None", the test uses the default instance's timeout period, which is 300 seconds. If the argument is "0", the test runs until the command returns.

    - `copy_to(localpath, remotepath)`: `scp localpath root@ip:remotepath`.

    - `copy_from(remotepath, localpath)`: `scp root@host:remotepath localpath`.

#### Instance Attributes

A single instance attribute exists, which is `target`. The `target` instance attribute is identical to the class attribute of the same name, which is described in the previous section. This attribute exists as both an instance and class attribute so tests can use `self.target.run(cmd)` in instance methods instead of `oeRuntimeTest.tc.target.run(cmd)`.

## Debugging With the GNU Project Debugger (GDB) Remotely

GDB allows you to examine running programs, which in turn helps you to understand and fix problems. It also allows you to perform post-mortem style analysis of program crashes. GDB is available as a package within the Yocto Project and is installed in SDK images by default. See the "Images" chapter in the Yocto Project Reference Manual for a description of these images. You can find information on GDB at .

For best results, install `-dbg` packages for the applications you are going to debug. Doing so makes extra debug symbols available that give you more meaningful output.

Sometimes, due to memory or disk space constraints, it is not possible to use GDB directly on the remote target to debug applications. These constraints arise because GDB needs to load the debugging information and the binaries of the process being debugged. Additionally, GDB needs to perform many computations to locate information such as function names, variable names and values, stack traces and so forth - even before starting the debugging process. These extra computations place more load on the target system and can alter the characteristics of the program being debugged.

To help get past the previously mentioned constraints, you can use Gdbserver. Gdbserver runs on the remote target and does not load any debugging information from the debugged process. Instead, a GDB instance processes the debugging information that is run on a remote computer - the host GDB. The host GDB then sends control commands to Gdbserver to make it stop or start the debugged program, as well as read or write memory regions of that debugged program. All the debugging information loaded and processed as well as all the heavy debugging is done by the host GDB. Offloading these processes gives the Gdbserver running on the target a chance to remain small and fast.

Because the host GDB is responsible for loading the debugging information and for doing the necessary processing to make actual debugging happen, the user has to make sure the host can access the unstripped binaries complete with their debugging information and also be sure the target is compiled with no optimizations. The host GDB must also have local access to all the libraries used by the debugged program. Because Gdbserver does not need any local debugging information, the binaries on the remote target can remain stripped. However, the binaries must also be compiled without optimization so they match the host's binaries.

To remain consistent with GDB documentation and terminology, the binary being debugged on the remote target machine is referred to as the "inferior" binary. For documentation on GDB see the GDB site.

The remainder of this section describes the steps you need to take to debug using the GNU project debugger.

### Set Up the Cross-Development Debugging Environment

Before you can initiate a remote debugging session, you need to be sure you have set up the cross-development environment, toolchain, and sysroot. The "Preparing for Application Development" chapter of the Yocto Project Application Developer's Guide describes this process. Be sure you have read that chapter and have set up your environment.

### Launch Gdbserver on the Target

Make sure Gdbserver is installed on the target. If it is not, install the package `gdbserver`, which needs the `libthread-db1` package.

Here is an example that when entered from the host connects to the target and launches Gdbserver in order to "debug" a binary named `helloworld`:

         $ gdbserver localhost:2345 /usr/bin/helloworld

Gdbserver should now be listening on port 2345 for debugging commands coming from a remote GDB process that is running on the host computer. Communication between Gdbserver and the host GDB are done using TCP. To use other communication protocols, please refer to the Gdbserver documentation.

### Launch GDB on the Host Computer

Running GDB on the host computer takes a number of stages, which this section describes.

#### Build the Cross-GDB Package

A suitable GDB cross-binary is required that runs on your host computer but also knows about the the ABI of the remote target. You can get this binary from the Cross-Development Toolchain. Here is an example where the toolchain has been installed in the default directory `/opt/poky/&DISTRO;`:

         /opt/poky/1.4/sysroots/i686-pokysdk-linux/usr/bin/armv7a-vfp-neon-poky-linux-gnueabi/arm-poky-linux-gnueabi-gdb

where `arm` is the target architecture and `linux-gnueabi` is the target ABI.

Alternatively, you can use BitBake to build the `gdb-cross` binary. Here is an example:

         $ bitbake gdb-cross

Once the binary is built, you can find it here:

         tmp/sysroots/<host-arch>/usr/bin/<target-platform>/<target-abi>-gdb

#### Create the GDB Initialization File and Point to Your Root Filesystem

Aside from the GDB cross-binary, you also need a GDB initialization file in the same top directory in which your binary resides. When you start GDB on your host development system, GDB finds this initialization file and executes all the commands within. For information on the `.gdbinit`, see "Debugging with GDB", which is maintained by sourceware.org.

You need to add a statement in the `.gdbinit` file that points to your root filesystem. Here is an example that points to the root filesystem for an ARM-based target device:

         set sysroot /home/jzhang/sysroot_arm

#### Launch the Host GDB

Before launching the host GDB, you need to be sure you have sourced the cross-debugging environment script, which if you installed the root filesystem in the default location is at `/opt/poky/&DISTRO;` and begins with the string "environment-setup". For more information, see the "Setting Up the Cross-Development Environment" section in the Yocto Project Application Developer's Guide.

Finally, switch to the directory where the binary resides and run the `cross-gdb` binary. Provide the binary file you are going to debug. For example, the following command continues with the example used in the previous section by loading the `helloworld` binary as well as the debugging information:

         $ arm-poky-linux-gnuabi-gdb helloworld

The commands in your `.gdbinit` execute and the GDB prompt appears.

### Connect to the Remote GDB Server

From the target, you need to connect to the remote GDB server that is running on the host. You need to specify the remote host and port. Here is the command continuing with the example:

         target remote 192.168.7.2:2345

### Use the Debugger

You can now proceed with debugging as normal - as if you were debugging on the local machine. For example, to instruct GDB to break in the "main" function and then continue with execution of the inferior binary use the following commands from within GDB:

         (gdb) break main
         (gdb) continue

For more information about using GDB, see the project's online documentation at .

## Examining Builds Using the Toaster API

Toaster is an Application Programming Interface (API) and web-based interface to the OpenEmbedded build system, which uses BitBake. Both interfaces are based on a Representational State Transfer (REST) API that queries for and returns build information using `GET` and `JSON`. These types of search operations retrieve sets of objects from a data store used to collect build information. The results contain all the data for the objects being returned. You can order the results of the search by key and the search parameters are consistent for all object types.

Using the interfaces you can do the following:

- See information about the tasks executed and reused during the build.

- See what is built (recipes and packages) and what packages were installed into the final image.

- See performance-related information such as build time, CPU usage, and disk I/O.

- Examine error, warning and trace messages to aid in debugging.

This release of Toaster provides you with information about a BitBake run. The tool does not allow you to configure and launch a build. However, future development includes plans to integrate the configuration and build launching capabilities of Hob.

For more information on using Hob to build an image, see the "Image Development Using Hob" section.

The remainder of this section describes what you need to have in place to use Toaster, how to start it, use it, and stop it. For additional information on installing and running Toaster, see the "Installation and Running" section of the "Toaster" wiki page. For complete information on the API and its search operation URI, parameters, and responses, see the REST API Contracts Wiki page.

### Starting Toaster

Getting set up to use and start Toaster is simple. First, be sure you have met the following requirements:

- You have set up your Source Directory by cloning the upstream `poky` repository. See the Yocto Project Release item for information on how to set up the Source Directory.

- You have checked out the `dora-toaster` branch:

           $ cd poky
           $ git checkout -b dora-toaster origin/dora-toaster

- Be sure your build machine has Django version 1.4.5 installed.

- Make sure that port 8000 and 8200 are free (i.e. they have no servers on them).

Once you have met the requirements, follow these steps to start Toaster running in the background of your shell:

1. Set up your build environment: Source a build environment script (i.e. `oe-init-build-env` or `oe-init-build-env-memres`).

2. Prepare your local configuration file: Toaster needs the Toaster class enabled in Bitbake in order to record target image package information. You can enable it by adding the following line to your `conf/local.conf` file:

            INHERIT += "toaster"

   Toaster also needs Build History enabled in Bitbake in order to record target image package information. You can enable this by adding the following two lines to your `conf/local.conf` file:

            INHERIT += "buildhistory"
            BUILDHISTORY_COMMIT = "1"

3. Start Toaster: Start the Toaster service using this command from within your build directory:

            $ source toaster start

The Toaster must be started and running in order for it to collect data.

When Toaster starts, it creates some additional files in your Build Directory. Deleting these files will cause you to lose data or interrupt Toaster:

- `toaster.sqlite`: Toaster's database file.

- `toaster_web.log`: The log file of the web server.

- `toaster_ui.log`: The log file of the user interface component.

- `toastermain.pid`: The PID of the web server.

- `toasterui.pid`: The PID of the DSI data bridge.

- `bitbake-cookerdaemon.log`: The BitBake server's log file.

### Using Toaster

Once Toaster is running, it logs information for any BitBake run from your Build Directory. This logging is automatic. All you need to do is access and use the information.

You access the information one of two ways:

- Open a Browser and type enter in the `http://localhost:8000` URL.

- Use the `xdg-open` tool from the shell and pass it the same URL.

Either method opens the home page for the Toaster interface, which is temporary for this release.

### Examining Toaster Data

The Toaster database is persistent regardless of whether you start or stop the service.

Toaster's interface shows you a list of builds (successful and unsuccessful) for which it has data. You can click on any build to see related information. This information includes configuration details, information about tasks, all recipes and packages built and their dependencies, packages installed in your final image, execution time, CPU usage and disk I/O per task.

### Stopping Toaster

Stop the Toaster service with the following command:

         $ source toaster stop

The service stops but the Toaster database remains persistent.

## Profiling with OProfile

OProfile is a statistical profiler well suited for finding performance bottlenecks in both user-space software and in the kernel. This profiler provides answers to questions like "Which functions does my application spend the most time in when doing X?" Because the OpenEmbedded build system is well integrated with OProfile, it makes profiling applications on target hardware straightforward.

For more information on how to set up and run OProfile, see the "OProfile" section in the Yocto Project Profiling and Tracing Manual.

To use OProfile, you need an image that has OProfile installed. The easiest way to do this is with `tools-profile` in the `IMAGE_FEATURES` variable. You also need debugging symbols to be available on the system where the analysis takes place. You can gain access to the symbols by using `dbg-pkgs` in the `IMAGE_FEATURES` variable or by installing the appropriate `-dbg` packages.

For successful call graph analysis, the binaries must preserve the frame pointer register and should also be compiled with the `-fno-omit-framepointer` flag. You can achieve this by setting the `SELECTED_OPTIMIZATION` variable with the following options:

         -fexpensive-optimizations
         -fno-omit-framepointer
         -frename-registers
         -O2

You can also achieve it by setting the `DEBUG_BUILD` variable to "1" in the `local.conf` configuration file. If you use the `DEBUG_BUILD` variable, you also add extra debugging information that can make the debug packages large.

### Profiling on the Target

Using OProfile you can perform all the profiling work on the target device. A simple OProfile session might look like the following:

         # opcontrol --reset
         # opcontrol --start --separate=lib --no-vmlinux -c 5
                  .
                  .
            [do whatever is being profiled]
                  .
                  .
         # opcontrol --stop
         $ opreport -cl

In this example, the `reset` command clears any previously profiled data. The next command starts OProfile. The options used when starting the profiler separate dynamic library data within applications, disable kernel profiling, and enable callgraphing up to five levels deep.

To profile the kernel, you would specify the `--vmlinux=/path/to/vmlinux` option. The `vmlinux` file is usually in the source directory in the `/boot/` directory and must match the running kernel.

After you perform your profiling tasks, the next command stops the profiler. After that, you can view results with the `opreport` command with options to see the separate library symbols and callgraph information.

Callgraphing logs information about time spent in functions and about a function's calling function (parent) and called functions (children). The higher the callgraphing depth, the more accurate the results. However, higher depths also increase the logging overhead. Consequently, you should take care when setting the callgraphing depth.

On ARM, binaries need to have the frame pointer enabled for callgraphing to work. To accomplish this use the `-fno-omit-framepointer` option with `gcc`.

For more information on using OProfile, see the OProfile online documentation at .

### Using OProfileUI

A graphical user interface for OProfile is also available. You can download and build this interface from the Yocto Project at . If the "tools-profile" image feature is selected, all necessary binaries are installed onto the target device for OProfileUI interaction. For a list of image features that ship with the Yocto Project, see the "Image Features" section in the Yocto Project Reference Manual.

Even though the source directory usually includes all needed patches on the target device, you might find you need other OProfile patches for recent OProfileUI features. If so, see the OProfileUI README for the most recent information.

#### Online Mode

Using OProfile in online mode assumes a working network connection with the target hardware. With this connection, you just need to run "oprofile-server" on the device. By default, OProfile listens on port 4224.

You can change the port using the `--port` command-line option.

The client program is called `oprofile-viewer` and its UI is relatively straightforward. You access key functionality through the buttons on the toolbar, which are duplicated in the menus. Here are the buttons:

- Connect: Connects to the remote host. You can also supply the IP address or hostname.

- Disconnect: Disconnects from the target.

- Start: Starts profiling on the device.

- Stop: Stops profiling on the device and downloads the data to the local host. Stopping the profiler generates the profile and displays it in the viewer.

- Download: Downloads the data from the target and generates the profile, which appears in the viewer.

- Reset: Resets the sample data on the device. Resetting the data removes sample information collected from previous sampling runs. Be sure you reset the data if you do not want to include old sample information.

- Save: Saves the data downloaded from the target to another directory for later examination.

- Open: Loads previously saved data.

The client downloads the complete 'profile archive' from the target to the host for processing. This archive is a directory that contains the sample data, the object files, and the debug information for the object files. The archive is then converted using the `oparchconv` script, which is included in this distribution. The script uses `opimport` to convert the archive from the target to something that can be processed on the host.

Downloaded archives reside in the Build Directory in `tmp` and are cleared up when they are no longer in use.

If you wish to perform kernel profiling, you need to be sure a `vmlinux` file that matches the running kernel is available. In the source directory, that file is usually located in `/boot/vmlinux-KERNELVERSION`, where `KERNEL-version` is the version of the kernel. The OpenEmbedded build system generates separate `vmlinux` packages for each kernel it builds. Thus, it should just be a question of making sure a matching package is installed (e.g. `opkg install kernel-vmlinux`). The files are automatically installed into development and profiling images alongside OProfile. A configuration option exists within the OProfileUI settings page that you can use to enter the location of the `vmlinux` file.

Waiting for debug symbols to transfer from the device can be slow, and it is not always necessary to actually have them on the device for OProfile use. All that is needed is a copy of the filesystem with the debug symbols present on the viewer system. The "Launch GDB on the Host Computer" section covers how to create such a directory with the Source Directory and how to use the OProfileUI Settings Dialog to specify the location. If you specify the directory, it will be used when the file checksums match those on the system you are profiling.

#### Offline Mode

If network access to the target is unavailable, you can generate an archive for processing in `oprofile-viewer` as follows:

         # opcontrol --reset
         # opcontrol --start --separate=lib --no-vmlinux -c 5
                .
                .
         [do whatever is being profiled]
                .
                .
         # opcontrol --stop
         # oparchive -o my_archive

In the above example, `my_archive` is the name of the archive directory where you would like the profile archive to be kept. After the directory is created, you can copy it to another host and load it using `oprofile-viewer` open functionality. If necessary, the archive is converted.

## Maintaining Open Source License Compliance During Your Product's Lifecycle

One of the concerns for a development organization using open source software is how to maintain compliance with various open source licensing during the lifecycle of the product. While this section does not provide legal advice or comprehensively cover all scenarios, it does present methods that you can use to assist you in meeting the compliance requirements during a software release.

With hundreds of different open source licenses that the Yocto Project tracks, it is difficult to know the requirements of each and every license. However, we can begin to cover the requirements of the major FLOSS licenses, by assuming that there are three main areas of concern:

- Source code must be provided.

- License text for the software must be provided.

- Compilation scripts and modifications to the source code must be provided.

There are other requirements beyond the scope of these three and the methods described in this section (e.g. the mechanism through which source code is distributed).

As different organizations have different methods of complying with open source licensing, this section is not meant to imply that there is only one single way to meet your compliance obligations, but rather to describe one method of achieving compliance. The remainder of this section describes methods supported to meet the previously mentioned three requirements. Once you take steps to meet these requirements, and prior to releasing images, sources, and the build system, you should audit all artifacts to ensure completeness.

The Yocto Project generates a license manifest during image creation that is located in `${DEPLOY_DIR}/licenses/<image_name-datestamp>` to assist with any audits.

### Providing the Source Code

Compliance activities should begin before you generate the final image. The first thing you should look at is the requirement that tops the list for most compliance groups - providing the source. The Yocto Project has a few ways of meeting this requirement.

One of the easiest ways to meet this requirement is to provide the entire `DL_DIR` used by the build. This method, however, has a few issues. The most obvious is the size of the directory since it includes all sources used in the build and not just the source used in the released image. It will include toolchain source, and other artifacts, which you would not generally release. However, the more serious issue for most companies is accidental release of proprietary software. The Yocto Project provides an archiver class to help avoid some of these concerns. See the "Archiving Sources - `archive*.bbclass`" section in the Yocto Project Reference Manual for information on this class.

Before you employ `DL_DIR` or the archiver class, you need to decide how you choose to provide source. The source archiver class can generate tarballs and SRPMs and can create them with various levels of compliance in mind. One way of doing this (but certainly not the only way) is to release just the original source as a tarball. You can do this by adding the following to the `local.conf` file found in the Build Directory:

         ARCHIVER_MODE ?= "original"
         ARCHIVER_CLASS = "${@'archive-${ARCHIVER_MODE}-source' if ARCHIVER_MODE != 'none' else ''}"
         INHERIT += "${ARCHIVER_CLASS}"
         SOURCE_ARCHIVE_PACKAGE_TYPE = "tar"

During the creation of your image, the source from all recipes that deploy packages to the image is placed within subdirectories of `DEPLOY_DIR/sources` based on the `LICENSE` for each recipe. Releasing the entire directory enables you to comply with requirements concerning providing the unmodified source. It is important to note that the size of the directory can get large.

A way to help mitigate the size issue is to only release tarballs for licenses that require the release of source. Let's assume you are only concerned with GPL code as identified with the following:

         $ cd poky/build/tmp/deploy/sources
         $ mkdir ~/gpl_source_release
         $ for dir in */*GPL*; do cp -r $dir ~/gpl_source_release; done

At this point, you could create a tarball from the `gpl_source_release` directory and provide that to the end user. This method would be a step toward achieving compliance with section 3a of GPLv2 and with section 6 of GPLv3.

### Providing License Text

One requirement that is often overlooked is inclusion of license text. This requirement also needs to be dealt with prior to generating the final image. Some licenses require the license text to accompany the binary. You can achieve this by adding the following to your `local.conf` file:

         COPY_LIC_MANIFEST = "1"
         COPY_LIC_DIRS = "1"

Adding these statements to the configuration file ensures that the licenses collected during package generation are included on your image. As the source archiver has already archived the original unmodified source that contains the license files, you would have already met the requirements for inclusion of the license information with source as defined by the GPL and other open source licenses.

### Providing Compilation Scripts and Source Code Modifications

At this point, we have addressed all we need to address prior to generating the image. The next two requirements are addressed during the final packaging of the release.

By releasing the version of the OpenEmbedded build system and the layers used during the build, you will be providing both compilation scripts and the source code modifications in one step.

If the deployment team has a BSP layer and a distro layer, and those those layers are used to patch, compile, package, or modify (in any way) any open source software included in your released images, you may be required to to release those layers under section 3 of GPLv2 or section 1 of GPLv3. One way of doing that is with a clean checkout of the version of the Yocto Project and layers used during your build. Here is an example:

         # We built using the &DISTRO_NAME; branch of the poky repo
         $ git clone -b &DISTRO_NAME; git://git.yoctoproject.org/poky
         $ cd poky
         # We built using the release_branch for our layers
         $ git clone -b release_branch git://git.mycompany.com/meta-my-bsp-layer
         $ git clone -b release_branch git://git.mycompany.com/meta-my-software-layer
         # clean up the .git repos
         $ find . -name ".git" -type d -exec rm -rf {} \;

One thing a development organization might want to consider for end-user convenience is to modify `meta-yocto/conf/bblayers.conf.sample` to ensure that when the end user utilizes the released build system to build an image, the development organization's layers are included in the `bblayers.conf` file automatically:

         # LAYER_CONF_VERSION is increased each time build/conf/bblayers.conf
         # changes incompatibly
         LCONF_VERSION = "6"

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

         BBLAYERS ?= " \
           ##OEROOT##/meta \
           ##OEROOT##/meta-yocto \
           ##OEROOT##/meta-yocto-bsp \
           ##OEROOT##/meta-mylayer \
           "

         BBLAYERS_NON_REMOVABLE ?= " \
           ##OEROOT##/meta \
           ##OEROOT##/meta-yocto \
           "

Creating and providing an archive of the Metadata layers (recipes, configuration files, and so forth) enables you to meet your requirements to include the scripts to control compilation as well as any modifications to the original source.