# 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 is 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-skeleton`, `meta-selftest`, `meta-poky`, 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 = "3"

   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-poky`, can choose to enforce their own precedence over `BBPATH`. For an example of that syntax, see the `layer.conf` file for the `meta-poky` 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 recipe might appear in multiple layers and allows you to choose the layer that takes 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 class files (`.bbclass`), 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. It is recommended, therefore, that you use unique class 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 an append file (`.bbappend`) to override only those parts of the original recipe you need to modify.

#### Avoid Duplicating Include Files

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

#### 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 "

  As an actual example, here's a line from the recipe for gnutls, which adds dependencies on "argp-standalone" when building with the musl C library:

           DEPENDS_append_libc-musl = " argp-standalone"

  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-poky \
           $HOME/poky/meta-yocto-bsp \
           $HOME/poky/meta-mylayer \
           "

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`:

         SUMMARY = "Device formfactor information"
         SECTION = "base"
         LICENSE = "MIT"
         LIC_FILES_CHKSUM = "file://${COREBASE}/LICENSE;md5=4d92cd373abda3937c2bc47fbc49d690 \
                        file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420"
         PR = "r45"

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

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

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

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 Raspberry Pi BSP Layer named `meta-raspberrypi`. 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-raspberrypi/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" as part of the `FILESEXTRAPATHS` 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, your append file would not even use the `FILESEXTRAPATHS` 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.

- `add-layer:` Adds a layer to `bblayers.conf`.

- `remove-layer:` Removes a layer from `bblayers.conf`

- `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-poky \
            /usr/local/src/yocto/meta-yocto-bsp \
            /usr/local/src/yocto/meta-mylayer \
            "

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 are in effect for every build and consequently affect all images, which 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 the `core-image-minimal` image 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`. This class lists out the available `IMAGE_FEATURES` of which most map to package groups while some, such as `debug-tweaks` and `read-only-rootfs`, resolve as general configuration settings.

In summary, the file looks at the contents of the `IMAGE_FEATURES` variable and then maps or configures the feature accordingly. Based on this information, the build system automatically adds the appropriate packages or configurations to the `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-full-cmdline` 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. `glibc-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-base.bb`.

If you examine that recipe, you see that the `PACKAGES` variable lists the package group packages to produce. The `inherit packagegroup` statement sets appropriate default values and automatically adds `-dev`, `-dbg`, and `-ptest` complementary packages for each package specified in the `PACKAGES` statement.

The `inherit packages` should be located near the top of the recipe, certainly before the `PACKAGES` statement.

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. You can see examples of these further down in the `packagegroup-base.bb` recipe.

Here is a short, fabricated example showing the same basic pieces:

         DESCRIPTION = "My Custom Package Groups"

         inherit packagegroup

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

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

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

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

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.

### Customizing an Image Hostname

By default, the configured hostname (i.e. `/etc/hostname`) in an image is the same as the machine name. For example, if `MACHINE` equals "qemux86", the configured hostname written to `/etc/hostname` is "qemux86".

You can customize this name by altering the value of the "hostname" variable in the `base-files` recipe using either an append file or a configuration file. Use the following in an append file:

         hostname="myhostname"

Use the following in a configuration file:

         hostname_pn-base-files = "myhostname"

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

Another point of interest is that if you unset the variable, the image will have no default hostname in the filesystem. Here is an example that unsets the variable in a configuration file:

         hostname_pn-base-files = ""

Having no default hostname in the filesystem is suitable for environments that use dynamic hostnames such as virtual machines.

## Writing a New Recipe

Recipes (`.bb` files) are fundamental components in the Yocto Project environment. Each software component built by the OpenEmbedded build system requires a recipe to define the component. This section describes how to create, write, and test a new recipe.

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.

### Overview

The following figure shows the basic process for creating a new recipe. The remainder of the section provides details for the steps.

### Locate or Automatically Create a Base Recipe

You can always write a recipe from scratch. However, three choices exist that can help you quickly get a start on a new recipe:

- `devtool add`: A command that assists in creating a recipe and an environment conducive to development.

- `recipetool create`: A command provided by the Yocto Project that automates creation of a base recipe based on the source files.

- Existing Recipes: Location and modification of an existing recipe that is similar in function to the recipe you need.

#### Creating the Base Recipe Using `devtool add`

The `devtool add` command uses the same logic for auto-creating the recipe as `recipetool create`, which is listed below. Additionally, however, `devtool add` sets up an environment that makes it easy for you to patch the source and to make changes to the recipe as is often necessary when adding a recipe to build a new piece of software to be included in a build.

You can find a complete description of the `devtool add` command in the "Use `devtool add` to Add an Application" section.

#### Creating the Base Recipe Using `recipetool create`

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

To run the tool, you just need to be in your Build Directory and have sourced the build environment setup script (i.e. `oe-init-build-env` or `oe-init-build-env-memres`). Here is the basic `recipetool` syntax:

Running `recipetool -h` or `recipetool create -h` produces the Python-generated help, which presented differently than what follows here.

         recipetool -h
         recipetool create [-h]
         recipetool [-d] [-q] [--color auto | always | never ] create -o OUTFILE [-m] [-x EXTERNALSRC] source

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

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

Running `recipetool create -o` OUTFILE creates the base recipe and locates it properly in the layer that contains your source files. Following are some syntax examples:

Use this syntax to generate a recipe based on source. Once generated, the recipe resides in the existing source code layer:

         recipetool create -o OUTFILE source

Use this syntax to generate a recipe using code that you extract from source. The extracted code is placed in its own layer defined by EXTERNALSRC.

         recipetool create -o OUTFILE -x EXTERNALSRC source

Use this syntax to generate a recipe based on source. The options direct `recipetool` to generate debugging information. Once generated, the recipe resides in the existing source code layer:

         recipetool create -d -o OUTFILE source

#### Locating and Using a Similar Recipe

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

Working from an existing recipe or a skeleton recipe is the best way to get started. Here are some points on both methods:

- Locate and modify a recipe that is close to what you want to do: This method works when you are familiar with the current recipe space. The method does not work so well for those new to the Yocto Project or writing recipes.

  Some risks associated with this method are using a recipe that has areas totally unrelated to what you are trying to accomplish with your recipe, not recognizing areas of the recipe that you might have to add from scratch, and so forth. All these risks stem from unfamiliarity with the existing recipe space.

- Use and modify the following skeleton recipe: If for some reason you do not want to use `recipetool` and you cannot find an existing recipe that is close to meeting your needs, you can use the following structure to provide the fundamental areas of a new recipe.

           DESCRIPTION = ""
           HOMEPAGE = ""
           LICENSE = ""
           SECTION = ""
           DEPENDS = ""
           LIC_FILES_CHKSUM = ""

           SRC_URI = ""

### Storing and Naming the Recipe

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

- Storing Your Recipe: The OpenEmbedded build system locates your recipe through the layer's `conf/layer.conf` file and the `BBFILES` variable. This variable sets up a path from which the build system can locate recipes. Here is the typical use:

           BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
                       ${LAYERDIR}/recipes-*/*/*.bbappend"

  Consequently, you need to be sure you locate your new recipe inside your layer such that it can be found.

  You can find more information on how layers are structured in the "Understanding and Creating Layers" section.

- Naming Your Recipe: When you name your recipe, you need to follow this naming convention:

           basename_version.bb

  Use lower-cased characters and do not include the reserved suffixes `-native`, `-cross`, `-initial`, or `-dev` casually (i.e. do not use them as part of your recipe name unless the string applies). Here are some examples:

           cups_1.7.0.bb
           gawk_4.0.2.bb
           irssi_0.8.16-rc1.bb

### Understanding Recipe Syntax

Understanding recipe file syntax is important for writing recipes. The following list overviews the basic items that make up a BitBake recipe file. For more complete BitBake syntax descriptions, see the "Syntax and Operators" chapter of the BitBake User Manual.

- Variable Assignments and Manipulations: Variable assignments allow a value to be assigned to a variable. The assignment can be static text or might include the contents of other variables. In addition to the assignment, appending and prepending operations are also supported.

  The following example shows some of the ways you can use variables in recipes:

           S = "${WORKDIR}/postfix-${PV}"
           CFLAGS += "-DNO_ASM"
           SRC_URI_append = " file://fixup.patch"

- Functions: Functions provide a series of actions to be performed. You usually use functions to override the default implementation of a task function or to complement a default function (i.e. append or prepend to an existing function). Standard functions use `sh` shell syntax, although access to OpenEmbedded variables and internal methods are also available.

  The following is an example function from the `sed` recipe:

           do_install () {
               autotools_do_install
               install -d ${D}${base_bindir}
               mv ${D}${bindir}/sed ${D}${base_bindir}/sed
               rmdir ${D}${bindir}/
           }

  It is also possible to implement new functions that are called between existing tasks as long as the new functions are not replacing or complementing the default functions. You can implement functions in Python instead of shell. Both of these options are not seen in the majority of recipes.

- Keywords: BitBake recipes use only a few keywords. You use keywords to include common functions (`inherit`), load parts of a recipe from other files (`include` and `require`) and export variables to the environment (`export`).

  The following example shows the use of some of these keywords:

           export POSTCONF = "${STAGING_BINDIR}/postconf"
           inherit autoconf
           require otherfile.inc

- Comments: Any lines that begin with the hash character (`#`) are treated as comment lines and are ignored:

           # This is a comment

This next list summarizes the most important and most commonly used parts of the recipe syntax. For more information on these parts of the syntax, you can reference the Syntax and Operators chapter in the BitBake User Manual.

- Line Continuation: `\` - Use the backward slash (`\`) character to split a statement over multiple lines. Place the slash character at the end of the line that is to be continued on the next line:

           VAR = "A really long \
                  line"

  You cannot have any characters including spaces or tabs after the slash character.

- Using Variables: `${...}` - Use the `${VARNAME}` syntax to access the contents of a variable:

           SRC_URI = "${SOURCEFORGE_MIRROR}/libpng/zlib-${PV}.tar.gz"

  It is important to understand that the value of a variable expressed in this form does not get substituted automatically. The expansion of these expressions happens on-demand later (e.g. usually when a function that makes reference to the variable executes). This behavior ensures that the values are most appropriate for the context in which they are finally used. On the rare occasion that you do need the variable expression to be expanded immediately, you can use the `:=` operator instead of `=` when you make the assignment, but this is not generally needed.

- Quote All Assignments: `"value"` - Use double quotes around the value in all variable assignments.

           VAR1 = "${OTHERVAR}"
           VAR2 = "The version is ${PV}"

- Conditional Assignment: `?=` - Conditional assignment is used to assign a value to a variable, but only when the variable is currently unset. Use the question mark followed by the equal sign (`?=`) to make a "soft" assignment used for conditional assignment. Typically, "soft" assignments are used in the `local.conf` file for variables that are allowed to come through from the external environment.

  Here is an example where `VAR1` is set to "New value" if it is currently empty. However, if `VAR1` has already been set, it remains unchanged:

           VAR1 ?= "New value"

  In this next example, `VAR1` is left with the value "Original value":

           VAR1 = "Original value"
           VAR1 ?= "New value"

- Appending: `+=` - Use the plus character followed by the equals sign (`+=`) to append values to existing variables.

  This operator adds a space between the existing content of the variable and the new content.

  Here is an example:

           SRC_URI += "file://fix-makefile.patch"

- Prepending: `=+` - Use the equals sign followed by the plus character (`=+`) to prepend values to existing variables.

  This operator adds a space between the new content and the existing content of the variable.

  Here is an example:

           VAR =+ "Starts"

- Appending: `_append` - Use the `_append` operator to append values to existing variables. This operator does not add any additional space. Also, the operator is applied after all the `+=`, and `=+` operators have been applied and after all `=` assignments have occurred.

  The following example shows the space being explicitly added to the start to ensure the appended value is not merged with the existing value:

           SRC_URI_append = " file://fix-makefile.patch"

  You can also use the `_append` operator with overrides, which results in the actions only being performed for the specified target or machine:

           SRC_URI_append_sh4 = " file://fix-makefile.patch"

- Prepending: `_prepend` - Use the `_prepend` operator to prepend values to existing variables. This operator does not add any additional space. Also, the operator is applied after all the `+=`, and `=+` operators have been applied and after all `=` assignments have occurred.

  The following example shows the space being explicitly added to the end to ensure the prepended value is not merged with the existing value:

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

  You can also use the `_prepend` operator with overrides, which results in the actions only being performed for the specified target or machine:

           CFLAGS_prepend_sh4 = "-I${S}/myincludes "

- Overrides: - You can use overrides to set a value conditionally, typically based on how the recipe is being built. For example, to set the `KBRANCH` variable's value to "standard/base" for any target `MACHINE`, except for qemuarm where it should be set to "standard/arm-versatile-926ejs", you would do the following:

           KBRANCH = "standard/base"
           KBRANCH_qemuarm  = "standard/arm-versatile-926ejs"

  Overrides are also used to separate alternate values of a variable in other situations. For example, when setting variables such as `FILES` and `RDEPENDS` that are specific to individual packages produced by a recipe, you should always use an override that specifies the name of the package.

- Indentation: Use spaces for indentation rather than than tabs. For shell functions, both currently work. However, it is a policy decision of the Yocto Project to use tabs in shell functions. Realize that some layers have a policy to use spaces for all indentation.

- Using Python for Complex Operations: `${@python_code}` - For more advanced processing, it is possible to use Python code during variable assignments (e.g. search and replacement on a variable).

  You indicate Python code using the `${@python_code}` syntax for the variable assignment:

           SRC_URI = "ftp://ftp.info-zip.org/pub/infozip/src/zip${@d.getVar('PV',1).replace('.', '')}.tgz

- Shell Function Syntax: Write shell functions as if you were writing a shell script when you describe a list of actions to take. You should ensure that your script works with a generic `sh` and that it does not require any `bash` or other shell-specific functionality. The same considerations apply to various system utilities (e.g. `sed`, `grep`, `awk`, and so forth) that you might wish to use. If in doubt, you should check with multiple implementations - including those from BusyBox.

### Running a Build on the Recipe

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

Assuming you have sourced a build environment setup script (i.e. `&OE_INIT_FILE;` or `oe-init-build-env-memres`) and you are in the Build Directory, use BitBake to process your recipe. All you need to provide is the `basename` of the recipe as described in the previous section:

         $ bitbake basename

During the build, the OpenEmbedded build system creates a temporary work directory for each recipe (`${` `WORKDIR` `}`) where it keeps extracted source files, log files, intermediate compilation and packaging files, and so forth.

The path to the per-recipe temporary work directory depends on the context in which it is being built. The quickest way to find this path is to have BitBake return it by running the following:

         $ bitbake -e basename | grep ^WORKDIR=

As an example, assume a Source Directory top-level folder named `poky`, a default Build Directory at `poky/build`, and a `qemux86-poky-linux` machine target system. Furthermore, suppose your recipe is named `foo_1.3.0.bb`. In this case, the work directory the build system uses to build the package would be as follows:

         poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0

Inside this directory you can find sub-directories such as `image`, `packages-split`, and `temp`. After the build, you can examine these to determine how well the build went.

You can find log files for each task in the recipe's `temp` directory (e.g. `poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0/temp`). Log files are named `log.taskname` (e.g. `log.do_configure`, `log.do_fetch`, and `log.do_compile`).

You can find more information about the build process in the "A Closer Look at the Yocto Project Development Environment" chapter of the Yocto Project Reference Manual.

### Fetching Code

The first thing your recipe must do is specify how to fetch the source files. Fetching is controlled mainly through the `SRC_URI` variable. Your recipe must have a `SRC_URI` variable that points to where the source is located. For a graphical representation of source locations, see the "Sources" section in the Yocto Project Reference Manual.

The `do_fetch` task uses the prefix of each entry in the `SRC_URI` variable value to determine which fetcher to use to get your source files. It is the `SRC_URI` variable that triggers the fetcher. The `do_patch` task uses the variable after source is fetched to apply patches. The OpenEmbedded build system uses `FILESOVERRIDES` for scanning directory locations for local files in `SRC_URI`.

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

Here is a simple example from the `meta/recipes-devtools/cdrtools/cdrtools-native_3.01a20.bb` recipe where the source comes from a single tarball. Notice the use of the `PV` variable:

         SRC_URI = "ftp://ftp.berlios.de/pub/cdrecord/alpha/cdrtools-${PV}.tar.bz2"

Files mentioned in `SRC_URI` whose names end in a typical archive extension (e.g. `.tar`, `.tar.gz`, `.tar.bz2`, `.zip`, and so forth), are automatically extracted during the `do_unpack` task. For another example that specifies these types of files, see the "Autotooled Package" section.

Another way of specifying source is from an SCM. For Git repositories, you must specify `SRCREV` and you should specify `PV` to include the revision with `SRCPV`. Here is an example from the recipe `meta/recipes-kernel/blktrace/blktrace_git.bb`:

         SRCREV = "d6918c8832793b4205ed3bfede78c2f915c23385"

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

         SRC_URI = "git://git.kernel.dk/blktrace.git \
                    file://ldflags.patch"

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

If your `SRC_URI` variable points to more than a single URL (excluding SCM URLs), you need to provide the `md5` and `sha256` checksums for each URL. For these cases, you provide a name for each URL as part of the `SRC_URI` and then reference that name in the subsequent checksum statements. Here is an example:

         SRC_URI = "${DEBIAN_MIRROR}/main/a/apmd/apmd_3.2.2.orig.tar.gz;name=tarball \
                    ${DEBIAN_MIRROR}/main/a/apmd/apmd_${PV}.diff.gz;name=patch"

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

         SRC_URI[patch.md5sum] = "57e1b689264ea80f78353519eece0c92"
         SRC_URI[patch.sha256sum] = "7905ff96be93d725544d0040e425c42f9c05580db3c272f11cff75b9aa89d430"

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

If no `SRC_URI` checksums are specified when you attempt to build the recipe, or you provide an incorrect checksum, the build will produce an error for each missing or incorrect checksum. As part of the error message, the build system provides the checksum string corresponding to the fetched file. Once you have the correct checksums, you can copy and paste them into your recipe and then run the build again to continue.

As mentioned, if the upstream source provides signatures for verifying the downloaded source code, you should verify those manually before setting the checksum values in the recipe and continuing with the build.

This final example is a bit more complicated and is from the `meta/recipes-sato/rxvt-unicode/rxvt-unicode_9.20.bb` recipe. The example's `SRC_URI` statement identifies multiple files as the source files for the recipe: a tarball, a patch file, a desktop file, and an icon.

         SRC_URI = "http://dist.schmorp.de/rxvt-unicode/Attic/rxvt-unicode-${PV}.tar.bz2 \
                    file://xwc.patch \
                    file://rxvt.desktop \
                    file://rxvt.png"

When you specify local files using the `file://` URI protocol, the build system fetches files from the local machine. The path is relative to the `FILESPATH` variable and searches specific directories in a certain order: `${` `BP` `}`, `${` `BPN` `}`, and `files`. The directories are assumed to be subdirectories of the directory in which the recipe or append file resides. For another example that specifies these types of files, see the "Single .c File Package (Hello World!)" section.

The previous example also specifies a patch file. Patch files are files whose names usually end in `.patch` or `.diff` but can end with compressed suffixes such as `diff.gz` and `patch.bz2`, for example. The build system automatically applies patches as described in the "Patching Code" section.

### Unpacking Code

During the build, the `do_unpack` task unpacks the source with `${` `S` `}` pointing to where it is unpacked.

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

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

### Patching Code

Sometimes it is necessary to patch code after it has been fetched. Any files mentioned in `SRC_URI` whose names end in `.patch` or `.diff` or compressed versions of these suffixes (e.g. `diff.gz` are treated as patches. The `do_patch` task automatically applies these patches.

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

As with all local files referenced in `SRC_URI` using `file://`, you should place patch files in a directory next to the recipe either named the same as the base name of the recipe (`BP` and `BPN`) or "files".

### Licensing

Your recipe needs to have both the `LICENSE` and `LIC_FILES_CHKSUM` variables:

- `LICENSE`: This variable specifies the license for the software. If you do not know the license under which the software you are building is distributed, you should go to the source code and look for that information. Typical files containing this information include `COPYING`, `LICENSE`, and `README` files. You could also find the information near the top of a source file. For example, given a piece of software licensed under the GNU General Public License version 2, you would set `LICENSE` as follows:

           LICENSE = "GPLv2"

  The licenses you specify within `LICENSE` can have any name as long as you do not use spaces, since spaces are used as separators between license names. For standard licenses, use the names of the files in `meta/files/common-licenses/` or the `SPDXLICENSEMAP` flag names defined in `meta/conf/licenses.conf`.

- `LIC_FILES_CHKSUM`: The OpenEmbedded build system uses this variable to make sure the license text has not changed. If it has, the build produces an error and it affords you the chance to figure it out and correct the problem.

  You need to specify all applicable licensing files for the software. At the end of the configuration step, the build process will compare the checksums of the files to be sure the text has not changed. Any differences result in an error with the message containing the current checksum. For more explanation and examples of how to set the `LIC_FILES_CHKSUM` variable, see the "Tracking License Changes" section in the Yocto Project Reference Manual.

  To determine the correct checksum string, you can list the appropriate files in the `LIC_FILES_CHKSUM` variable with incorrect md5 strings, attempt to build the software, and then note the resulting error messages that will report the correct md5 strings. See the "Fetching Code" section for additional information.

  Here is an example that assumes the software has a `COPYING` file:

           LIC_FILES_CHKSUM = "file://COPYING;md5=xxx"

  When you try to build the software, the build system will produce an error and give you the correct string that you can substitute into the recipe file for a subsequent build.

### Dependencies

Most software packages have a short list of other packages that they require, which are called dependencies. These dependencies fall into two main categories: build-time dependencies, which are required when the software is built; and runtime dependencies, which are required to be installed on the target in order for the software to run.

Within a recipe, you specify build-time dependencies using the `DEPENDS` variable. Although nuances exist, items specified in `DEPENDS` should be names of other recipes. It is important that you specify all build-time dependencies explicitly. If you do not, due to the parallel nature of BitBake's execution, you can end up with a race condition where the dependency is present for one task of a recipe (e.g. `do_configure`) and then gone when the next task runs (e.g. `do_compile`).

Another consideration is that configure scripts might automatically check for optional dependencies and enable corresponding functionality if those dependencies are found. This behavior means that to ensure deterministic results and thus avoid more race conditions, you need to either explicitly specify these dependencies as well, or tell the configure script explicitly to disable the functionality. If you wish to make a recipe that is more generally useful (e.g. publish the recipe in a layer for others to use), instead of hard-disabling the functionality, you can use the `PACKAGECONFIG` variable to allow functionality and the corresponding dependencies to be enabled and disabled easily by other users of the recipe.

Similar to build-time dependencies, you specify runtime dependencies through a variable - `RDEPENDS`, which is package-specific. All variables that are package-specific need to have the name of the package added to the end as an override. Since the main package for a recipe has the same name as the recipe, and the recipe's name can be found through the `${` `PN` `}` variable, then you specify the dependencies for the main package by setting `RDEPENDS_${PN}`. If the package were named `${PN}-tools`, then you would set `RDEPENDS_${PN}-tools`, and so forth.

Some runtime dependencies will be set automatically at packaging time. These dependencies include any shared library dependencies (i.e. if a package "example" contains "libexample" and another package "mypackage" contains a binary that links to "libexample" then the OpenEmbedded build system will automatically add a runtime dependency to "mypackage" on "example"). See the "Automatically Added Runtime Dependencies" in the Yocto Project Reference Manual for further details.

### Configuring the Recipe

Most software provides some means of setting build-time configuration options before compilation. Typically, setting these options is accomplished by running a configure script with some options, or by modifying a build configuration file.

As of Yocto Project Release 1.7, some of the core recipes that package binary configuration scripts now disable the scripts due to the scripts previously requiring error-prone path substitution. The OpenEmbedded build system uses `pkg-config` now, which is much more robust. You can find a list of the `*-config` scripts that are disabled list in the "Binary Configuration Scripts Disabled" section in the Yocto Project Reference Manual.

A major part of build-time configuration is about checking for build-time dependencies and possibly enabling optional functionality as a result. You need to specify any build-time dependencies for the software you are building in your recipe's `DEPENDS` value, in terms of other recipes that satisfy those dependencies. You can often find build-time or runtime dependencies described in the software's documentation.

The following list provides configuration items of note based on how your software is built:

- Autotools: If your source files have a `configure.ac` file, then your software is built using Autotools. If this is the case, you just need to worry about modifying the configuration.

  When using Autotools, your recipe needs to inherit the `autotools` class and your recipe does not have to contain a `do_configure` task. However, you might still want to make some adjustments. For example, you can set `EXTRA_OECONF` or `PACKAGECONFIG_CONFARGS` to pass any needed configure options that are specific to the recipe.

- CMake: If your source files have a `CMakeLists.txt` file, then your software is built using CMake. If this is the case, you just need to worry about modifying the configuration.

  When you use CMake, your recipe needs to inherit the `cmake` class and your recipe does not have to contain a `do_configure` task. You can make some adjustments by setting `EXTRA_OECMAKE` to pass any needed configure options that are specific to the recipe.

- Other: If your source files do not have a `configure.ac` or `CMakeLists.txt` file, then your software is built using some method other than Autotools or CMake. If this is the case, you normally need to provide a `do_configure` task in your recipe unless, of course, there is nothing to configure.

  Even if your software is not being built by Autotools or CMake, you still might not need to deal with any configuration issues. You need to determine if configuration is even a required step. You might need to modify a Makefile or some configuration file used for the build to specify necessary build options. Or, perhaps you might need to run a provided, custom configure script with the appropriate options.

  For the case involving a custom configure script, you would run `./configure --help` and look for the options you need to set.

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

### Compilation

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

However, if the compile step fails, you need to diagnose the failure. Here are some common issues that cause failures.

For cases where improper paths are detected for configuration files or for when libraries/headers cannot be found, be sure you are using the more robust `pkg-config`. See the note in section "Configuring the Recipe" for additional information.

- Parallel build failures: These failures manifest themselves as intermittent errors, or errors reporting that a file or directory that should be created by some other part of the build process could not be found. This type of failure can occur even if, upon inspection, the file or directory does exist after the build has failed, because that part of the build process happened in the wrong order.

  To fix the problem, you need to either satisfy the missing dependency in the Makefile or whatever script produced the Makefile, or (as a workaround) set `PARALLEL_MAKE` to an empty string:

           PARALLEL_MAKE = ""

  For information on parallel Makefile issues, see the "Debugging Parallel Make Races" section.

- Improper host path usage: This failure applies to recipes building for the target or `nativesdk` only. The failure occurs when the compilation process uses improper headers, libraries, or other files from the host system when cross-compiling for the target.

  To fix the problem, examine the `log.do_compile` file to identify the host paths being used (e.g. `/usr/include`, `/usr/lib`, and so forth) and then either add configure options, apply a patch, or do both.

- Failure to find required libraries/headers: If a build-time dependency is missing because it has not been declared in `DEPENDS`, or because the dependency exists but the path used by the build process to find the file is incorrect and the configure step did not detect it, the compilation process could fail. For either of these failures, the compilation process notes that files could not be found. In these cases, you need to go back and add additional options to the configure script as well as possibly add additional build-time dependencies to `DEPENDS`.

  Occasionally, it is necessary to apply a patch to the source to ensure the correct paths are used. If you need to specify paths to find files staged into the sysroot from other recipes, use the variables that the OpenEmbedded build system provides (e.g. `STAGING_BINDIR`, `STAGING_INCDIR`, `STAGING_DATADIR`, and so forth).

### Installing

During `do_install`, the task copies the built files along with their hierarchy to locations that would mirror their locations on the target device. The installation process copies files from the `${` `S` `}`, `${` `B` `}`, and `${` `WORKDIR` `}` directories to the `${` `D` `}` directory to create the structure as it should appear on the target system.

How your software is built affects what you must do to be sure your software is installed correctly. The following list describes what you must do for installation depending on the type of build system used by the software being built:

- Autotools and CMake: If the software your recipe is building uses Autotools or CMake, the OpenEmbedded build system understands how to install the software. Consequently, you do not have to have a `do_install` task as part of your recipe. You just need to make sure the install portion of the build completes with no issues. However, if you wish to install additional files not already being installed by `make install`, you should do this using a `do_install_append` function using the install command as described in the "Manual" bulleted item later in this list.

- Other (using `make install`): You need to define a `do_install` function in your recipe. The function should call `oe_runmake install` and will likely need to pass in the destination directory as well. How you pass that path is dependent on how the `Makefile` being run is written (e.g. `DESTDIR=${D}`, `PREFIX=${D}`, `INSTALLROOT=${D}`, and so forth).

  For an example recipe using `make install`, see the "Makefile-Based Package" section.

- Manual: You need to define a `do_install` function in your recipe. The function must first use `install -d` to create the directories under `${` `D` `}`. Once the directories exist, your function can use `install` to manually install the built software into the directories.

  You can find more information on `install` at .

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

#### Notes

- During the installation process, you might need to modify some of the installed files to suit the target layout. For example, you might need to replace hard-coded paths in an initscript with values of variables provided by the build system, such as replacing `/usr/bin/` with `${bindir}`. If you do perform such modifications during `do_install`, be sure to modify the destination file after copying rather than before copying. Modifying after copying ensures that the build system can re-execute `do_install` if needed.

- `oe_runmake install`, which can be run directly or can be run indirectly by the `autotools` and `cmake` classes, runs `make install` in parallel. Sometimes, a Makefile can have missing dependencies between targets that can result in race conditions. If you experience intermittent failures during `do_install`, you might be able to work around them by disabling parallel Makefile installs by adding the following to the recipe:

           PARALLEL_MAKEINST = ""

  See `PARALLEL_MAKEINST` for additional information.

### Enabling System Services

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

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

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

The OpenEmbedded build system provides support for starting services two different ways:

- SysVinit: SysVinit is a system and service manager that manages the init system used to control the very basic functions of your system. The init program is the first program started by the Linux kernel when the system boots. Init then controls the startup, running and shutdown of all other programs.

  To enable a service using SysVinit, your recipe needs to inherit the `update-rc.d` class. The class helps facilitate safely installing the package on the target.

  You will need to set the `INITSCRIPT_PACKAGES`, `INITSCRIPT_NAME`, and `INITSCRIPT_PARAMS` variables within your recipe.

- systemd: System Management Daemon (systemd) was designed to replace SysVinit and to provide enhanced management of services. For more information on systemd, see the systemd homepage at .

  To enable a service using systemd, your recipe needs to inherit the `systemd` class. See the `systemd.bbclass` file located in your Source Directory. section for more information.

### Packaging

Successful packaging is a combination of automated processes performed by the OpenEmbedded build system and some specific steps you need to take. The following list describes the process:

- Splitting Files: The `do_package` task splits the files produced by the recipe into logical components. Even software that produces a single binary might still have debug symbols, documentation, and other logical components that should be split out. The `do_package` task ensures that files are split up and packaged correctly.

- Running QA Checks: The `insane` class adds a step to the package generation process so that output quality assurance checks are generated by the OpenEmbedded build system. This step performs a range of checks to be sure the build's output is free of common problems that show up during runtime. For information on these checks, see the `insane` class and the "QA Error and Warning Messages" chapter in the Yocto Project Reference Manual.

- Hand-Checking Your Packages: After you build your software, you need to be sure your packages are correct. Examine the `${` `WORKDIR` `}/packages-split` directory and make sure files are where you expect them to be. If you discover problems, you can set `PACKAGES`, `FILES`, `do_install(_append)`, and so forth as needed.

- Splitting an Application into Multiple Packages: If you need to split an application into several packages, see the "Splitting an Application into Multiple Packages" section for an example.

- Installing a Post-Installation Script: For an example showing how to install a post-installation script, see the "Post-Installation Scripts" section.

- Marking Package Architecture: Depending on what your recipe is building and how it is configured, it might be important to mark the packages produced as being specific to a particular machine, or to mark them as not being specific to a particular machine or architecture at all.

  By default, packages apply to any machine with the same architecture as the target machine. When a recipe produces packages that are machine-specific (e.g. the `MACHINE` value is passed into the configure script or a patch is applied only for a particular machine), you should mark them as such by adding the following to the recipe:

           PACKAGE_ARCH = "${MACHINE_ARCH}"

  On the other hand, if the recipe produces packages that do not contain anything specific to the target machine or architecture at all (e.g. recipes that simply package script files or configuration files), you should use the `allarch` class to do this for you by adding this to your recipe:

           inherit allarch

  Ensuring that the package architecture is correct is not critical while you are doing the first few builds of your recipe. However, it is important in order to ensure that your recipe rebuilds (or does not rebuild) appropriately in response to changes in configuration, and to ensure that you get the appropriate packages installed on the target machine, particularly if you run separate builds for more than one target machine.

### Sharing Files Between Recipes

Recipes often need to use files provided by other recipes on the build host. For example, an application linking to a common library needs access to the library itself and its associated headers. The way this access is accomplished is by populating sysroot with files. One sysroot exists per "machine" for which the image is being built. In practical terms, this means a sysroot exists for the target machine, and a sysroot exists for the build host.

You could find the term "staging" used within the Yocto project regarding files populating sysroot (e.g. the `STAGING_DIR` variable).

Recipes should never populate the sysroot directly (i.e. write files into sysroot). Instead, files should be installed into standard locations during the `do_install` task within the `${` `D` `}` directory.

A subset of these files, as defined by the the `SYSROOT_DIRS` variable, automatically populates the sysroot. The reason for this limitation is that almost all files that populate the sysroot are cataloged in manifests in order to ensure the files can be removed later when a recipe is either modified or removed. Thus, the sysroot is able to remain free from stale files.

It is possible to modify the list of directories that populate the sysroot. The following example shows how you could add the `/opt` directory to the list of directories:

         SYSROOT_DIRS += "/opt"

For information on variables you can use to help control how files sysroot is populated, see the `SYSROOT_DIRS`, `SYSROOT_DIRS_NATIVE`, and `SYSROOT_DIRS_BLACKLIST` variables.

### Properly Versioning Pre-Release Recipes

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

In order to ensure the versions compare properly, the recommended convention is to set `PV` within the recipe to "previous_version+current_version". You can use an additional variable so that you can use the current version elsewhere. Here is an example:

         REALPV = "0.8.16-rc1"
         PV = "0.8.15+${REALPV}"

### Post-Installation Scripts

Post-installation scripts run immediately after installing a package on the target or during image creation when a package is included in an image. To add a post-installation script to a package, add a `pkg_postinst_PACKAGENAME()` function to the recipe file (`.bb`) and replace `PACKAGENAME` with the name of the package you want to attach to the `postinst` script. To apply the post-installation script to the main package for the recipe, which is usually what is required, specify `${` `PN` `}` in place of `PACKAGENAME`.

A post-installation function has the following structure:

         pkg_postinst_PACKAGENAME() {
         # 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.

Any RPM post-installation script that runs on the target should return a 0 exit code. RPM does not allow non-zero exit codes for these scripts, and the RPM package manager will cause the package to fail installation on the target.

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() {
         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 environment variable `D` 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.

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

### Testing

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

For information on how to customize your image by adding specific packages, see the "Customizing Images" section.

### Examples

To help summarize how to write a recipe, this section provides some examples given various scenarios:

- Recipes that use local files

- Using an Autotooled package

- Using a Makefile-based package

- Splitting an application into multiple packages

- Adding binaries to an image

#### 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.

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

         SRC_URI = "file://helloworld.c"

         S = "${WORKDIR}"

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

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

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 inherit the `autotools` class, which contains the definitions of all the steps needed to build an Autotool-based application. The result of the build is automatically packaged. And, if the application uses NLS for localization, packages with local information are generated (one package per language). Following is one example: (`hello_2.3.bb`)

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

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

         inherit autotools gettext

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` or `PACKAGECONFIG_CONFARGS` variables. BitBake passes these options into the GNU `make` 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:

         SUMMARY = "Tools for managing memory technology devices"
         SECTION = "base"
         DEPENDS = "zlib lzo e2fsprogs util-linux"
         HOMEPAGE = "http://www.linux-mtd.infradead.org/"
         LICENSE = "GPLv2+"
         LIC_FILES_CHKSUM = "file://COPYING;md5=0636e73ff0215e8d672dc4c32c317bb3 \
                             file://include/common.h;beginline=1;endline=17;md5=ba05b07912a44ea2bf81ce409380049c"

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

         PV = "1.5.1+git${SRCPV}"

         S = "${WORKDIR}/git"

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

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

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

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

         PARALLEL_MAKE = ""

         BBCLASSEXTEND = "native"

#### 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

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

         XORG_PN = "libXpm"

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

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.

#### Packaging Externally Produced Binaries

Sometimes, you need to add pre-compiled binaries to an image. For example, suppose that binaries for proprietary code exist, which are created by a particular division of a company. Your part of the company needs to use those binaries as part of an image that you are building using the OpenEmbedded build system. Since you only have the binaries and not the source code, you cannot use a typical recipe that expects to fetch the source specified in `SRC_URI` and then compile it.

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

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

##### Notes

- Using `DEPENDS` is a good idea even for components distributed in binary form, and is often necessary for shared libraries. For a shared library, listing the library dependencies in `DEPENDS` makes sure that the libraries are available in the staging sysroot when other recipes link against the library, which might be necessary for successful linking.

- Using `DEPENDS` also allows runtime dependencies between packages to be added automatically. See the "Automatically Added Runtime Dependencies" section in the Yocto Project Reference Manual for more information.

If you cannot use the `bin_package` class, you need to be sure you are doing the following:

- Create a recipe where the `do_configure` and `do_compile` tasks do nothing: It is usually sufficient to just not define these tasks in the recipe, because the default implementations do nothing unless a Makefile is found in `${` `S` `}`.

  If `${S}` might contain a Makefile, or if you inherit some class that replaces `do_configure` and `do_compile` with custom versions, then you can use the `[` `noexec` `]` flag to turn the tasks into no-ops, as follows:

           do_configure[noexec] = "1"
           do_compile[noexec] = "1"

  Unlike `deleting the tasks`, using the flag preserves the dependency chain from the `do_fetch`, `do_unpack`, and `do_patch` tasks to the `do_install` task.

- Make sure your `do_install` task installs the binaries appropriately.

- Ensure that you set up `FILES` (usually `FILES_${` `PN` `}`) to point to the files you have installed, which of course depends on where you have installed them and whether those files are in different locations than the defaults.

### Following Recipe Style Guidelines

When writing recipes, it is good to conform to existing style guidelines. The OpenEmbedded Styleguide wiki page provides rough guidelines for preferred recipe style.

It is common for existing recipes to deviate a bit from this style. However, aiming for at least a consistent style is a good idea. Some practices, such as omitting spaces around `=` operators in assignments or ordering recipe components in an erratic way, are widely seen as poor style.

## Adding a New Machine

Adding a new machine to the Yocto Project is a straightforward process. This section describes how to add machines that are similar to those that the Yocto Project already supports.

Although well within the capabilities of the Yocto Project, adding a totally new architecture might require changes to `gcc/glibc` 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" section in the Yocto Project Board Support Package (BSP) Developer's Guide.

### Adding the Machine Configuration File

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

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

The most important variables you must set in your machine configuration file or include from a lower-level configuration file are as follows:

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

- `PREFERRED_PROVIDER_virtual/kernel`

- `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 existing machine `.conf` files from `meta-yocto-bsp/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 kernel recipe. You can find several kernel recipe examples in the Source Directory at `meta/recipes-kernel/linux` that you can use as references.

If you are creating a new kernel 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 `do_configure` task that configures the unpacked kernel with a `defconfig` file. 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 recipe, 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 recipe. 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)'

For more information on `defconfig` files, see the "Changing the Configuration" section in the Yocto Project Linux Kernel Development Manual.

### 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" machine:

         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

## Building Targets with Multiple Configurations

Bitbake also has functionality that allows you to build multiple targets at the same time, where each target uses a different configuration.

In order to accomplish this, you setup each of the configurations you need to use in parallel by placing the configuration files in your current build directory alongside the usual `local.conf` file.

Follow these guidelines to create an environment that supports multiple configurations:

- Create Configuration Files: You need to create a single configuration file for each configuration for which you want to add support. These files would contain lines such as the following:

           MACHINE = "A"

  The files would contain any other variables that can be set and built in the same directory.

  You can change the `TMPDIR` to not conflict.

  Furthermore, the configuration file must be located in the current build directory in a directory named `multiconfig` under the build's `conf` directory where `local.conf` resides. The reason for this restriction is because the `BBPATH` variable is not constructed until the layers are parsed. Consequently, using the configuration file as a pre-configuration file is not possible unless it is located in the current working directory.

- Add the BitBake Multi-Config Variable to you Local Configuration File: Use the `BBMULTICONFIG` variable in your `conf/local.conf` configuration file to specify each separate configuration. For example, the following line tells BitBake it should load `conf/multiconfig/configA.conf`, `conf/multiconfig/configB.conf`, and `conf/multiconfig/configC.conf`.

           BBMULTICONFIG = "configA configB configC"

- Launch BitBake: Use the following BitBake command form to launch the build:

           $ bitbake [multiconfig:multiconfigname:]target [[[multiconfig:multiconfigname:]target] ... ]

  Following is an example that supports building a minimal image for configuration A alongside a standard `core-image-sato`, which takes its configuration from `local.conf`:

           $ bitbake multiconfig:configA:core-image-minimal core-image-sato

Support for multiple configurations in this current release of the Yocto Project (&DISTRO_NAME; &DISTRO;) has some known issues:

- No inter-multi-configuration dependencies exist.

- Shared State (sstate) optimizations do not exist. Consequently, if the build uses the same object twice in, for example, two different `TMPDIR` directories, the build will either load from an existing sstate cache at the start or build the object twice.

## 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 includes `${PN}-staticdev`, which represents 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, where you can see how the static library files are defined:

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

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

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

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

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

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

### 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 a different set of libraries. The libraries could differ in architecture, compiler options, or other optimizations.

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 not be needed.

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_append = " lib32-glib-2.0"

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-glib-2.0` 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-glib-2.0

#### Additional Implementation Details

Generic implementation details as well as details that are specific to package management systems exist. Following are implementation details that exist regardless of the package management system:

- The typical convention used for the class extension code as used by Multilib assumes that all package names specified in `PACKAGES` that contain `${PN}` have `${PN}` at the start of the name. When that convention is not followed and `${PN}` appears at the middle or the end of a name, problems occur.

- The `TARGET_VENDOR` value under Multilib will be extended to "-vendormlmultilib" (e.g. "-pokymllib32" for a "lib32" Multilib with Poky). The reason for this slightly unwieldy contraction is that any "-" characters in the vendor string presently break Autoconf's `config.sub`, and other separators are problematic for different reasons.

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 straightforward as long as the libraries use proper versioning. With properly versioned libraries, all you need to do to individually specify the libraries is create separate, appropriately named recipes where the `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"

## Enabling GObject Introspection Support

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

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

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

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

### Enabling the Generation of Introspection Data

Enabling the generation of introspection data (GIR files) in your library package involves the following:

1. Inherit the `gobject-introspection` class.

2. Make sure introspection is not disabled anywhere in the recipe or from anything the recipe includes. Also, make sure that "gobject-introspection-data" is not in `DISTRO_FEATURES_BACKFILL_CONSIDERED` and that "qemu-usermode" is not in `MACHINE_FEATURES_BACKFILL_CONSIDERED`. If either of these conditions exist, nothing will happen.

3. Try to build the recipe. If you encounter build errors that look like something is unable to find `.so` libraries, check where these libraries are located in the source tree and add the following to the recipe:

            GIR_EXTRA_LIBS_PATH = "${B}/something/.libs"

   See recipes in the `oe-core` repository that use that `GIR_EXTRA_LIBS_PATH` variable as an example.

4. Look for any other errors, which probably mean that introspection support in a package is not entirely standard, and thus breaks down in a cross-compilation environment. For such cases, custom-made fixes are needed. A good place to ask and receive help in these cases is the Yocto Project mailing lists.

Using a library that no longer builds against the latest Yocto Project release and prints introspection related errors is a good candidate for the previous procedure.

### Disabling the Generation of Introspection Data

You might find that you do not want to generate introspection data. Or, perhaps QEMU does not work on your build host and target architecture combination. If so, you can use either of the following methods to disable GIR file generations:

- Add the following to your distro configuration:

           DISTRO_FEATURES_BACKFILL_CONSIDERED = "gobject-introspection-data"

  Adding this statement disables generating introspection data using QEMU but will still enable building introspection tools and libraries (i.e. building them does not require the use of QEMU).

- Add the following to your machine configuration:

           MACHINE_FEATURES_BACKFILL_CONSIDERED = "qemu-usermode"

  Adding this statement disables the use of QEMU when building packages for your machine. Currently, this feature is used only by introspection recipes and has the same effect as the previously described option.

  Future releases of the Yocto Project might have other features affected by this option.

If you disable introspection data, you can still obtain it through other means such as copying the data from a suitable sysroot, or by generating it on the target hardware. The OpenEmbedded build system does not currently provide specific support for these techniques.

### Testing that Introspection Works in an Image

Use the following procedure to test if generating introspection data is working in an image:

1. Make sure that "gobject-introspection-data" is not in `DISTRO_FEATURES_BACKFILL_CONSIDERED` and that "qemu-usermode" is not in `MACHINE_FEATURES_BACKFILL_CONSIDERED`.

2. Build `core-image-sato`.

3. Launch a Terminal and then start Python in the terminal.

4. Enter the following in the terminal:

            >>> from gi.repository import GLib
            >>> GLib.get_host_name()

5. For something a little more advanced, enter the following:

            http://python-gtk-3-tutorial.readthedocs.org/en/latest/introduction.html

### Known Issues

The following know issues exist for GObject Introspection Support:

- `qemu-ppc64` immediately crashes. Consequently, you cannot build introspection data on that architecture.

- x32 is not supported by QEMU. Consequently, introspection data is disabled.

- musl causes transient GLib binaries to crash on assertion failures. Consequently, generating introspection data is disabled.

- Because QEMU is not able to run the binaries correctly, introspection is disabled for some specific packages under specific architectures (e.g. `gcr`, `libsecret`, and `webkit`).

- QEMU usermode might not work properly when running 64-bit binaries under 32-bit host machines. In particular, "qemumips64" is known to not work under i686.

## Optionally Using an External Toolchain

You might want to use an external toolchain as part of your development. If this is the case, the fundamental steps you need to accomplish are as follows:

- Understand where the installed toolchain resides. For cases where you need to build the external toolchain, you would need to take separate steps to build and install the toolchain.

- Make sure you add the layer that contains the toolchain to your `bblayers.conf` file through the `BBLAYERS` variable.

- Set the `EXTERNAL_TOOLCHAIN` variable in your `local.conf` file to the location in which you installed the toolchain.

A good example of an external toolchain used with the Yocto Project is Mentor Graphics Sourcery G++ Toolchain. You can see information on how to use that particular layer in the `README` file at . You can find further information by reading about the `TCMODE` variable in the Yocto Project Reference Manual's variable glossary.

## 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, Wic, to create the properly partitioned image.

You can generate partitioned images (image`.wic`) two ways: using the OpenEmbedded build system and by running the OpenEmbedded Image Creator Wic directly. The former way is preferable as it is easier to use and understand.

### Creating Partitioned Images

The OpenEmbedded build system can generate partitioned images the same way as it generates any other image type. To generate a partitioned image, you need to modify two variables.

- Include "wic" as part of the `IMAGE_FSTYPES` variable.

- Include the name of the wic kickstart file as part of the `WKS_FILE` variable

Further steps to generate a partitioned image are the same as for any other image type. For information on image types, see the "Building Images" section.

### Using OpenEmbedded Image Creator Wic to Generate Partitioned Images

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 as shown with the `wic list images` command in the "Using an Existing Kickstart File" section. When you apply the command 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.

The `wic` command and the infrastructure it is based on is by definition incomplete. The purpose of the command is to allow the generation of customized images, and as such, was designed to be completely extensible through a plug-in interface. See the "Plug-ins" section for information on these plug-ins.

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 the `wic` utility, 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 to 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 existing functionality in OE Core's `image-live` class and `mkefidisk.sh` script. The difference between Wic and those examples is that with Wic the functionality of those scripts is implemented by a general-purpose partitioning language, which is based on Redhat kickstart syntax.

#### Requirements

In order to use the `wic` utility with the OpenEmbedded Build system, your system needs 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 the list of distributions that support the Yocto Project.

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

- You need to have the build artifacts already available, which typically means that you must have already created an image using the Openembedded build system (e.g. `core-image-minimal`). While it might seem redundant to generate an image in order to create an image using Wic, the current version of Wic requires the artifacts in the form generated by the build system.

- You must build several native tools, which are tools built to run on the build system:

           $ bitbake parted-native dosfstools-native mtools-native

- 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` command 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
                        with command being either
                        create or list.

You can also get detailed help on a number of topics from the help system. The output of `wic --help` displays a list of available help topics under a "Help topics" heading. You can have the help system display the help text for a given topic by prefacing the topic with `wic help`:

         $ wic help help_topic

You can find out more about the images Wic creates using the existing kickstart files with the following form of the command:

         $ wic list image help

with `image` being either `directdisk` or `mkefidisk`.

#### Operational Modes

You can use Wic in two different modes, depending on how much control you need for specifying the Openembedded build artifacts that are used for creating the image: Raw and Cooked:

- 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.

Regardless of the mode you use, you need to have the build artifacts ready and available. Additionally, the environment must be set up using the `&OE_INIT_FILE;` or `oe-init-build-env-memres` script found in the Build Directory.

##### Raw Mode

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

         $ wic create image_name.wks [options] [...]

           Where:

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

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

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

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

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

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

              -k KERNEL_DIR, --kernel-dir=KERNEL_DIR
                 The path to the directory containing the kernel to use
                 in the .wks boot image.

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

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

              -D, --debug
                  Output debug information.

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

##### Cooked Mode

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

         $ wic create kickstart_file -e image_name

           Where:

               kickstart_file
                   An OpenEmbedded kickstart file. You can provide your own
                   custom file or a supplied file.

               image_name
                   Specifies the image built using the OpenEmbedded build
                   system.

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.

#### Using an Existing Kickstart File

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

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

When you use an existing 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-efi --ondisk sda --label msdos --active --align 1024

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

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

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

#### 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 an Existing 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

The previous example shows the easiest way to create an image by running in Cooked Mode and using the `-e` option with an existing 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 the exact image 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 at empanada ~]$ sudo eject /dev/sdb

##### Using a Modified Kickstart File

Because partitioned 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 existing 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 by 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-pcbios --ondisk sdb --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 at 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.

#### Plug-ins

Plug-ins allow Wic functionality to be extended and specialized by users. This section documents the plug-in interface, which is currently restricted to source plug-ins.

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

A source plug-in is created as a subclass of `SourcePlugin`. The plug-in file containing it is added to `scripts/lib/wic/plugins/source/` to make the plug-in implementation available to the Wic implementation. For more information, see `scripts/lib/wic/pluginbase.py`.

Source plug-ins can also be implemented and added by external layers. As such, any plug-ins found in a `scripts/lib/wic/plugins/source/` directory in an external layer are also made available.

When the Wic implementation needs to invoke a partition-specific implementation, it looks for the plug-in that has the same name as the `--source` parameter given to that partition. For example, if the partition is set up as follows:

         part /boot --source bootimg-pcbios   ...

The methods defined as class members of the plug-in having the matching `bootimg-pcbios.name` class member are used.

To be more concrete, here is the plug-in definition that matches a `--source bootimg-pcbios` usage, along with an example method called by the Wic implementation when it needs to invoke an implementation-specific partition-preparation function:

        class BootimgPcbiosPlugin(SourcePlugin):
            name = 'bootimg-pcbios'

        @classmethod
            def do_prepare_partition(self, part, ...)

If the subclass itself does not implement a function, a default version in a superclass is located and used, which is why all plug-ins must be derived from `SourcePlugin`.

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

- `do_prepare_partition()`: Called to do the actual content population for a partition. In other words, the method prepares the final partition image that is incorporated into the disk image.

- `do_configure_partition()`: Called before `do_prepare_partition()`. This method is typically used to create custom configuration files for a partition (e.g. syslinux or grub configuration files).

- `do_install_disk()`: Called after all partitions have been prepared and assembled into a disk image. This method provides a hook to allow finalization of a disk image, (e.g. writing an MBR).

- `do_stage_partition()`: Special content-staging hook called before `do_prepare_partition()`. This method is normally empty.

  Typically, a partition just uses the passed-in parameters (e.g. the unmodified value of `bootimg_dir`). However, in some cases things might need to be more tailored. As an example, certain files might additionally need to be taken from `bootimg_dir + /boot`. This hook allows those files to be staged in a customized fashion.

  `get_bitbake_var()` allows you to access non-standard variables that you might want to use for this.

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

#### OpenEmbedded Kickstart (`.wks`) Reference

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

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

The following is a list of the commands, their syntax, and meanings. The commands are based on the Fedora kickstart versions but with modifications to reflect Wic capabilities. You can see the original documentation for those commands at the following links:

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

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

##### Command: part or partition

Either of these commands create a partition on the system and use the following syntax:

         part [mntpoint]
         partition [mntpoint]

If you do not provide mntpoint, Wic creates a partition but does not mount it.

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

- `/path`: For example, `/`, `/usr`, or `/home`

- `swap`: The created partition is used as swap space.

Specifying a mntpoint causes the partition to automatically be mounted. Wic achieves this by adding entries to the filesystem table (fstab) during image generation. In order for wic to generate a valid fstab, you must also provide one of the `--ondrive`, `--ondisk`, or `--use-uuid` partition options as part of the command. Here is an example using "/" as the mountpoint. The command uses "--ondisk" to force the partition onto the `sdb` disk:

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

Here is a list that describes other supported options you can use with the `part` and `partition` commands:

- `--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 names the source of the data that populates the partition. The most common value for this option is "rootfs", but you can use any value that maps to a valid source plug-in. For information on the source plug-ins, see the "Plug-ins" section.

  If you use `--source rootfs`, Wic creates a partition as large as needed and to fill it with the contents of the root filesystem pointed to by the `-r` command-line option or the equivalent rootfs derived from the `-e` command-line option. The filesystem type used to create the partition is driven by the value of the `--fstype` option specified for the partition. See the entry on `--fstype` that follows for more information.

  If you use `--source plugin-name`, Wic creates a partition as large as needed and fills it with the contents of the partition that is generated by the specified plug-in name using the data pointed to by the `-r` command-line option or the equivalent rootfs derived from the `-e` command-line option. Exactly what those contents and filesystem type end up being are dependent on the given plug-in implementation.

  If you do not use the `--source` option, the `wic` command creates an empty partition. Consequently, you must use the `--size` option to specify the size of the empty partition.

- `--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:

  - `ext4`

  - `ext3`

  - `ext2`

  - `btrfs`

  - `squashfs`

  - `swap`

- `--fsoptions`: Specifies a free-form string of options to be used when mounting the filesystem. This string will be copied into the `/etc/fstab` file of the installed system and should be enclosed in quotes. If not specified, the default string is "defaults".

- `--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 a Wic-specific option that says to start a partition on an x KBytes boundary.

- `--no-table`: This option is a Wic-specific option. Using the option reserves space for the partition and causes it to become populated. However, the partition is not added to the partition table.

- `--extra-space`: This option is a Wic-specific option that adds extra space after the space filled by the content of the partition. The final size can go beyond the size specified by the `--size` option. The default value is 10 Mbytes.

- `--overhead-factor`: This option is a Wic-specific option that multiplies the size of the partition by the option's value. You must supply a value greater than or equal to "1". The default value is "1.3".

- `--part-type`: This option is a Wic-specific option that specifies the partition type globally unique identifier (GUID) for GPT partitions. You can find the list of partition type GUIDs at .

- `--use-uuid`: This option is a Wic-specific option that causes Wic to generate a random GUID for the partition. The generated identifier is used in the bootloader configuration to specify the root partition.

- `--uuid`: This option is a Wic-specific option that specifies the partition UUID.

##### Command: bootloader

This command specifies how the bootloader should be configured and supports the following options:

Bootloader functionality and boot partitions are implemented by the various `--source` plug-ins that implement bootloader functionality. The bootloader command essentially provides a means of modifying bootloader configuration.

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

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

- `--configfile`: Specifies a user-defined configuration file for the bootloader. You can provide a full pathname for the file or a file that exists in the `canned-wks` folder. This option overrides all other bootloader options.

## Building an Initial RAM Filesystem (initramfs) Image

initramfs is the successor of Initial RAM Disk (initrd). It is a "copy in and out" (cpio) archive of the initial file system that gets loaded into memory during the Linux startup process. Because Linux uses the contents of the archive during initialization, the initramfs needs to contain all of the device drivers and tools needed to mount the final root filesystem.

To build an initramfs image and bundle it into the kernel, set the `INITRAMFS_IMAGE_BUNDLE` variable in your `local.conf` file, and set the `INITRAMFS_IMAGE` variable in your `machine.conf` file:

         INITRAMFS_IMAGE_BUNDLE = "1"
         INITRAMFS_IMAGE = "image_recipe_name"

Setting the `INITRAMFS_IMAGE_BUNDLE` flag causes the initramfs created by the recipe and defined by `INITRAMFS_IMAGE` to be unpacked into the `${B}/usr/` directory. The unpacked initramfs is then passed to the kernel's `Makefile` using the `CONFIG_INITRAMFS_SOURCE` variable, allowing initramfs to be built in to the kernel normally.

The preferred method is to use the `INITRAMFS_IMAGE` variable rather than the `INITRAMFS_TASK` variable. Setting `INITRAMFS_TASK` is supported for backward compatibility. However, use of this variable has circular dependency problems. See the `INITRAMFS_IMAGE_BUNDLE` variable for additional information on these dependency problems.

The recipe that `INITRAMFS_IMAGE` points to must produce a `.cpio.gz`, `.cpio.tar`, `.cpio.lz4`, `.cpio.lzma`, or `.cpio.xz` file. You can ensure you produce one of these `.cpio.*` files by setting the `INITRAMFS_FSTYPES` variable in your configuration file to one or more of the above file types.

If you add items to the initramfs image by way of its recipe, you should use `PACKAGE_INSTALL` rather than `IMAGE_INSTALL`. `PACKAGE_INSTALL` gives more direct control of what is added to the image as compared to the defaults you might not necessarily want that are set by the `image` or `core-image` classes.

## 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. You can also save known configurations in a `defconfig` file that the build system can use for kernel configuration.

This section describes how to use `menuconfig`, create and use configuration fragments, and how to interactively modify 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. You must also be sure of the state of your build in the Source Directory. The following commands run `menuconfig` assuming the Source Directory's top-level folder is `~/poky`:

         $ cd poky
         $ source oe-init-build-env
         $ bitbake linux-yocto -c kernel_configme -f
         $ 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-3.14` 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 3.14 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-3.14.11+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-3.14...` 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 as you want and save them, then compare the renamed configuration file against the newly created file. You can use the resulting differences as your base to create configuration fragments to permanently save in your kernel layer.

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 a `defconfig` File

A `defconfig` file is simply a `.config` renamed to "defconfig". You can use a `defconfig` file to retain a known set of kernel configurations from which the OpenEmbedded build system can draw to create the final `.config` file.

Out-of-the-box, the Yocto Project never ships a `defconfig` or `.config` file. The OpenEmbedded build system creates the final `.config` file used to configure the kernel.

To create a `defconfig`, start with a complete, working Linux kernel `.config` file. Copy that file to the appropriate `${` `PN` `}` directory in your layer's `recipes-kernel/linux` directory, and rename the copied file to "defconfig". Then, add the following lines to the linux-yocto `.bbappend` file in your layer:

         FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
         SRC_URI += "file://defconfig"

The `SRC_URI` tells the build system how to search for the file, while the `FILESEXTRAPATHS` extends the `FILESPATH` variable (search directories) to include the `${PN}` directory you created to hold the configuration changes.

The build system applies the configurations from the `defconfig` file before applying any subsequent configuration fragments. The final kernel configuration is a combination of the configurations in the `defconfig` file and any configuration fragments you provide. You need to realize that if you have any configuration fragments, the build system applies these on top of and after applying the existing defconfig file configurations.

For more information on configuring the kernel, see the "Changing the Configuration" and "Generating Configuration Files" sections, both in the Yocto Project Linux Kernel Development Manual.

### 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:

         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 fragment 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 fragment files? You can place these files in the same area pointed to by `SRC_URI`. The OpenEmbedded build system picks up the configuration and adds it to the kernel's configuration. For example, suppose you had a set of configuration options in a file called `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 `do_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 `do_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 configuration 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 `do_kernel_configme` and `do_kernel_configcheck` tasks.

3. Take the resulting list of files from the `do_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 `do_kernel_configme` and `do_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.

### Determining Hardware and Non-Hardware Features for the Kernel Configuration Audit Phase

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

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

To determine whether or not a given option is "hardware" or "non-hardware", the kernel Metadata contains files that classify individual or groups of options as either hardware or non-hardware. To better show this, consider a situation where the Yocto Project kernel cache contains the following files:

         kernel-cache/features/drm-psb/hardware.cfg
         kernel-cache/features/kgdb/hardware.cfg
         kernel-cache/ktypes/base/hardware.cfg
         kernel-cache/bsp/mti-malta32/hardware.cfg
         kernel-cache/bsp/fsl-mpc8315e-rdb/hardware.cfg
         kernel-cache/bsp/qemu-ppc32/hardware.cfg
         kernel-cache/bsp/qemuarma9/hardware.cfg
         kernel-cache/bsp/mti-malta64/hardware.cfg
         kernel-cache/bsp/arm-versatile-926ejs/hardware.cfg
         kernel-cache/bsp/common-pc/hardware.cfg
         kernel-cache/bsp/common-pc-64/hardware.cfg
         kernel-cache/features/rfkill/non-hardware.cfg
         kernel-cache/ktypes/base/non-hardware.cfg
         kernel-cache/features/aufs/non-hardware.kcf
         kernel-cache/features/ocf/non-hardware.kcf
         kernel-cache/ktypes/base/non-hardware.kcf
         kernel-cache/ktypes/base/hardware.kcf
         kernel-cache/bsp/qemu-ppc32/hardware.kcf

The following list provides explanations for the various files:

- `hardware.kcf`: Specifies a list of kernel Kconfig files that contain hardware options only.

- `non-hardware.kcf`: Specifies a list of kernel Kconfig files that contain non-hardware options only.

- `hardware.cfg`: Specifies a list of kernel `CONFIG_` options that are hardware, regardless of whether or not they are within a Kconfig file specified by a hardware or non-hardware Kconfig file (i.e. `hardware.kcf` or `non-hardware.kcf`).

- `non-hardware.cfg`: Specifies a list of kernel `CONFIG_` options that are not hardware, regardless of whether or not they are within a Kconfig file specified by a hardware or non-hardware Kconfig file (i.e. `hardware.kcf` or `non-hardware.kcf`).

Here is a specific example using the `kernel-cache/bsp/mti-malta32/hardware.cfg`:

         CONFIG_SERIAL_8250
         CONFIG_SERIAL_8250_CONSOLE
         CONFIG_SERIAL_8250_NR_UARTS
         CONFIG_SERIAL_8250_PCI
         CONFIG_SERIAL_CORE
         CONFIG_SERIAL_CORE_CONSOLE
         CONFIG_VGA_ARB

The kernel configuration audit automatically detects these files (hence the names must be exactly the ones discussed here), and uses them as inputs when generating warnings about the final `.config` file.

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

## 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.

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. Rather than use the `yocto-layer` script to create the layer, this example steps through the process by hand. If you want information on the script that creates a general layer, see the "Creating a General Layer Using the yocto-layer Script" section.

These two commands create a directory you can use for your layer:

         $ 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 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: `devtool` and Quilt. 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"

   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-poky`, and `meta-yocto-bsp` in the `poky` Git repository. Add the path to your `meta-mylayer` location:

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

### 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 using BitBake to run from within the Build Directory the `do_cleansstate` task as follows:

            $ 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. For information on the clean tasks, see the "`do_clean`", "`do_cleanall`", and "`do_cleansstate`" sections all in the Yocto Project Reference Manual.

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.

## Making Images More Secure

Security is of increasing concern for embedded devices. Consider the issues and problems discussed in just this sampling of work found across the Internet:

- "Security Risks of Embedded Systems" by Bruce Schneier

- "Internet Census 2012" by Carna Botnet

- "Security Issues for Embedded Devices" by Jake Edge

When securing your image is of concern, there are steps, tools, and variables that you can consider to help you reach the security goals you need for your particular device. Not all situations are identical when it comes to making an image secure. Consequently, this section provides some guidance and suggestions for consideration when you want to make your image more secure.

Because the security requirements and risks are different for every type of device, this section cannot provide a complete reference on securing your custom OS. It is strongly recommended that you also consult other sources of information on embedded Linux system hardening and on security.

### General Considerations

General considerations exist that help you create more secure images. You should consider the following suggestions to help make your device more secure:

- Scan additional code you are adding to the system (e.g. application code) by using static analysis tools. Look for buffer overflows and other potential security problems.

- Pay particular attention to the security for any web-based administration interface.

  Web interfaces typically need to perform administrative functions and tend to need to run with elevated privileges. Thus, the consequences resulting from the interface's security becoming compromised can be serious. Look for common web vulnerabilities such as cross-site-scripting (XSS), unvalidated inputs, and so forth.

  As with system passwords, the default credentials for accessing a web-based interface should not be the same across all devices. This is particularly true if the interface is enabled by default as it can be assumed that many end-users will not change the credentials.

- Ensure you can update the software on the device to mitigate vulnerabilities discovered in the future. This consideration especially applies when your device is network-enabled.

- Ensure you remove or disable debugging functionality before producing the final image. For information on how to do this, see the "Considerations Specific to the OpenEmbedded Build System" section.

- Ensure you have no network services listening that are not needed.

- Remove any software from the image that is not needed.

- Enable hardware support for secure boot functionality when your device supports this functionality.

### Security Flags

The Yocto Project has security flags that you can enable that help make your build output more secure. The security flags are in the `meta/conf/distro/include/security_flags.inc` file in your Source Directory (e.g. `poky`).

Depending on the recipe, certain security flags are enabled and disabled by default.

Use the following line in your `local.conf` file or in your custom distribution configuration file to enable the security compiler and linker flags for your build:

         require conf/distro/include/security_flags.inc

### Considerations Specific to the OpenEmbedded Build System

You can take some steps that are specific to the OpenEmbedded build system to make your images more secure:

- Ensure "debug-tweaks" is not one of your selected `IMAGE_FEATURES`. When creating a new project, the default is to provide you with an initial `local.conf` file that enables this feature using the `EXTRA_IMAGE_FEATURES` variable with the line:

           EXTRA_IMAGE_FEATURES = "debug-tweaks"

  To disable that feature, simply comment out that line in your `local.conf` file, or make sure `IMAGE_FEATURES` does not contain "debug-tweaks" before producing your final image. Among other things, leaving this in place sets the root password as blank, which makes logging in for debugging or inspection easy during development but also means anyone can easily log in during production.

- It is possible to set a root password for the image and also to set passwords for any extra users you might add (e.g. administrative or service type users). When you set up passwords for multiple images or users, you should not duplicate passwords.

  To set up passwords, use the `extrausers` class, which is the preferred method. For an example on how to set up both root and user passwords, see the "`extrausers.bbclass`" section.

  When adding extra user accounts or setting a root password, be cautious about setting the same password on every device. If you do this, and the password you have set is exposed, then every device is now potentially compromised. If you need this access but want to ensure security, consider setting a different, random password for each device. Typically, you do this as a separate step after you deploy the image onto the device.

- Consider enabling a Mandatory Access Control (MAC) framework such as SMACK or SELinux and tuning it appropriately for your device's usage. You can find more information in the `meta-selinux` layer.

### Tools for Hardening Your Image

The Yocto Project provides tools for making your image more secure. You can find these tools in the `meta-security` layer of the Yocto Project Source Repositories.

## 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
           DISTRO_VERSION

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

           DISTRO_FEATURES
           DISTRO_EXTRA_RDEPENDS
           DISTRO_EXTRA_RRECOMMENDS
           TCLIBC

  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 an append file (`.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.

## Creating a Custom Template Configuration Directory

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

The OpenEmbedded build system uses the environment variable `TEMPLATECONF` to locate the directory from which it gathers configuration information that ultimately ends up in the Build Directory's `conf` directory. By default, `TEMPLATECONF` is set as follows in the `poky` repository:

         TEMPLATECONF=${TEMPLATECONF:-meta-poky/conf}

This is the directory used by the build system to find templates from which to build some key configuration files. If you look at this directory, you will see the `bblayers.conf.sample`, `local.conf.sample`, and `conf-notes.txt` files. The build system uses these files to form the respective `bblayers.conf` file, `local.conf` file, and display the list of BitBake targets when running the setup script.

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

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

         TEMPLATECONF=${TEMPLATECONF:-meta-mylayer/myconf}

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

Here is the default list of targets displayed as a result of running either of the setup scripts:

         You can now run 'bitbake <target>'

         Common targets are:
             core-image-minimal
             core-image-sato
             meta-toolchain
             meta-ide-support

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

## 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 help 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 repositories (i.e. `linux-yocto-3.14`, `linux-yocto-3.10`, `linux-yocto-3.8`, and so forth) 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 modify 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, 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:

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

  1. Remove `glibc` 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 `glibc` features provide the support and restore the configuration.

  4. Rebuild and repeat the process.

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

## Building Images for More than One Machine

A common scenario developers face is creating images for several different machines that use the same software environment. In this situation, it is tempting to set the tunings and optimization flags for each build specifically for the targeted hardware (i.e. "maxing out" the tunings). Doing so can considerably add to build times and package feed maintenance collectively for the machines. For example, selecting tunes that are extremely specific to a CPU core used in a system might enable some micro optimizations in GCC for that particular system but would otherwise not gain you much of a performance difference across the other systems as compared to using a more general tuning across all the builds (e.g. setting `DEFAULTTUNE` specifically for each machine's build). Rather than "max out" each build's tunings, you can take steps that cause the OpenEmbedded build system to reuse software across the various machines where it makes sense.

If build speed and package feed maintenance are considerations, you should consider the points in this section that can help you optimize your tunings to best consider build times and package feed maintenance.

- Share the Build Directory: If at all possible, share the `TMPDIR` across builds. The Yocto Project supports switching between different `MACHINE` values in the same `TMPDIR`. This practice is well supported and regularly used by developers when building for multiple machines. When you use the same `TMPDIR` for multiple machine builds, the OpenEmbedded build system can reuse the existing native and often cross-recipes for multiple machines. Thus, build time decreases.

  If `DISTRO` settings change or fundamental configuration settings such as the filesystem layout, you need to work with a clean `TMPDIR`. Sharing `TMPDIR` under these circumstances might work but since it is not guaranteed, you should use a clean `TMPDIR`.

- Enable the Appropriate Package Architecture: By default, the OpenEmbedded build system enables three levels of package architectures: "all", "tune" or "package", and "machine". Any given recipe usually selects one of these package architectures (types) for its output. Depending for what a given recipe creates packages, making sure you enable the appropriate package architecture can directly impact the build time.

  A recipe that just generates scripts can enable "all" architecture because there are no binaries to build. To specifically enable "all" architecture, be sure your recipe inherits the `allarch` class. This class is useful for "all" architectures because it configures many variables so packages can be used across multiple architectures.

  If your recipe needs to generate packages that are machine-specific or when one of the build or runtime dependencies is already machine-architecture dependent, which makes your recipe also machine-architecture dependent, make sure your recipe enables the "machine" package architecture through the `MACHINE_ARCH` variable:

           PACKAGE_ARCH = "${MACHINE_ARCH}"

  When you do not specifically enable a package architecture through the `PACKAGE_ARCH`, The OpenEmbedded build system defaults to the `TUNE_PKGARCH` setting:

           PACKAGE_ARCH = "${TUNE_PKGARCH}"

- Choose a Generic Tuning File if Possible: Some tunes are more generic and can run on multiple targets (e.g. an `armv5` set of packages could run on `armv6` and `armv7` processors in most cases). Similarly, `i486` binaries could work on `i586` and higher processors. You should realize, however, that advances on newer processor versions would not be used.

  If you select the same tune for several different machines, the OpenEmbedded build system reuses software previously built, thus speeding up the overall build time. Realize that even though a new sysroot for each machine is generated, the software is not recompiled and only one package feed exists.

- Manage Granular Level Packaging: Sometimes cases exist where injecting another level of package architecture beyond the three higher levels noted earlier can be useful. For example, consider the `emgd` graphics stack in the `meta-intel` layer. In this layer, a subset of software exists that is compiled against something different from the rest of the generic packages. You can examine the key code in the Source Repositories "daisy" branch in `classes/emgd-gl.bbclass`. For a specific set of packages, the code redefines `PACKAGE_ARCH`. `PACKAGE_EXTRA_ARCHS` is then appended with this extra tune name in `meta-intel-emgd.inc`. The result is that when searching for packages, the build system uses a four-level search and the packages in this new level are preferred as compared to the standard tune. The overall result is that the build system reuses most software from the common tune except for specific cases as needed.

- Use Tools to Debug Issues: Sometimes you can run into situations where software is being rebuilt when you think it should not be. For example, the OpenEmbedded build system might not be using shared state between machines when you think it should be. These types of situations are usually due to references to machine-specific variables such as `MACHINE`, `SERIAL_CONSOLE`, `XSERVER`, `MACHINE_FEATURES`, and so forth in code that is supposed to only be tune-specific or when the recipe depends (`DEPENDS`, `RDEPENDS`, `RRECOMMENDS`, `RSUGGESTS`, and so forth) on some other recipe that already has `PACKAGE_ARCH` defined as "${MACHINE_ARCH}".

  Patches to fix any issues identified are most welcome as these issues occasionally do occur.

  For such cases, you can use some tools to help you sort out the situation:

  - `sstate-diff-machines.sh`: You can find this tool in the `scripts` directory of the Source Repositories. See the comments in the script for information on how to use the tool.

  - BitBake's "-S printdiff" Option: Using this option causes BitBake to try to establish the closest signature match it can (e.g. in the shared state cache) and then run `bitbake-diffsigs` over the matches to determine the stamps and delta where these two stamp trees diverge.

## Working with Packages

This section describes a few tasks that involve packages:

- Excluding packages from an image

- Incrementing a package revision number

- 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 --host ip --port port --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 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 used 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
         summary
            Summary to set for each package. Must include %s;
            defaults to description if not set.

#### 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 of which you need to be aware in order to provide support for runtime package management.

When BitBake generates packages, it needs to know what format or formats to use. In your configuration, you use the `PACKAGE_CLASSES` variable to specify the format:

1. Open the `local.conf` file inside your Build Directory (e.g. `~/poky/build/conf/local.conf`).

2. Select the desired package format as follows:

            PACKAGE_CLASSES ?= “package_packageformat”

   where packageformat can be "ipk", "rpm", and "deb", which are the supported package formats.

   Because the Yocto Project supports three different package formats, you can set the variable with more than one argument. However, the OpenEmbedded build system only uses the first argument when creating an image or Software Development Kit (SDK).

If you would like your image to start off with a basic package database containing the packages in your current build as well as to 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

The reason for this restriction 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.

You can use the `PACKAGE_FEED_ARCHS`, `PACKAGE_FEED_BASE_PATHS`, and `PACKAGE_FEED_URIS` variables to pre-configure target images to use a package feed. If you do not define these variables, then manual steps as described in the subsequent sections are necessary to configure the target. You should set these variables before building the image in order to produce a correctly configured image.

When your build is complete, your packages reside in the `${TMPDIR}/deploy/packageformat` directory. For example, if `${` `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

Although other protocols are possible, a server using HTTP typically serves packages. If you want to use HTTP, then set up and configure a web server such as Apache 2, lighttpd, or SimpleHTTPServer on the machine serving the packages.

To keep things simple, this section describes how to set up a SimpleHTTPServer web server to share package feeds from the developer's machine. Although this server might not be the best for a production environment, the setup is simple and straight forward. Should you want to use a different server more suited for production (e.g. Apache 2, Lighttpd, or Nginx), take the appropriate steps to do so.

From within the build directory where you have built an image based on your packaging choice (i.e. the `PACKAGE_CLASSES` setting), simply start the server. The following example assumes a build directory of `~/poky/build/tmp/deploy/rpm` and a `PACKAGE_CLASSES` setting of "package_rpm":

         $ cd ~/poky/build/tmp/deploy/rpm
         $ python -m SimpleHTTPServer

#### Target Setup

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

##### Using RPM

The `smart` application performs runtime package management of RPM packages. You must perform an initial setup for `smart` on the target machine if the `PACKAGE_FEED_ARCHS`, `PACKAGE_FEED_BASE_PATHS`, and `PACKAGE_FEED_URIS` variables have not been set or the target image was built before the variables were set.

As an example, assume the target is able to use the following package databases: `all`, `i586`, and `qemux86` from a server named `my.server`. You must inform `smart` of the availability of these databases by issuing the following commands on the target:

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

From the target machine, fetch the repository:

         # smart update

After everything is set up, `smart` is able to find, install, and upgrade packages from the specified repository.

##### Using IPK

The `opkg` application performs runtime package management of IPK packages. You must perform an initial setup for `opkg` on the target machine if the `PACKAGE_FEED_ARCHS`, `PACKAGE_FEED_BASE_PATHS`, and `PACKAGE_FEED_URIS` variables have not been set or the target image was built before the variables were set.

The `opkg` application uses configuration files to find available package databases. Thus, you need to create a configuration file inside the `/etc/opkg/` direction, which informs `opkg` of any repository you want to use.

As an example, suppose you are serving packages from a `ipk/` directory containing the `i586`, `all`, and `qemux86` databases through an HTTP server named `my.server`. On the target, create a configuration file (e.g. `my_repo.conf`) inside the `/etc/opkg/` directory containing the following:

         src/gz all http://my.server/ipk/all
         src/gz i586 http://my.server/ipk/i586
         src/gz qemux86 http://my.server/ipk/qemux86

Next, instruct `opkg` to fetch the repository information:

         # opkg update

The `opkg` application is now able to find, install, and upgrade packages from the specified repository.

##### Using DEB

The `apt` application performs runtime package management of DEB packages. This application uses a source list file to find available package databases. You must perform an initial setup for `apt` on the target machine if the `PACKAGE_FEED_ARCHS`, `PACKAGE_FEED_BASE_PATHS`, and `PACKAGE_FEED_URIS` variables have not been set or the target image was built before the variables were set.

To inform `apt` of the repository you want to use, you might create a list file (e.g. `my_repo.list`) inside the `/etc/apt/sources.list.d/` directory. As an example, suppose you are serving packages from a `deb/` directory containing the `i586`, `all`, and `qemux86` databases through an HTTP server named `my.server`. The list file should contain:

         deb http://my.server/deb/all ./
         deb http://my.server/deb/i586 ./
         deb http://my.server/deb/qemux86 ./

Next, instruct the `apt` application to fetch the repository information:

         # apt-get update

After this step, `apt` is able to find, install, and upgrade packages from the specified repository.

### 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 the test. 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.

For a list of Yocto Project recipes that are already enabled with ptest, see the Ptest wiki page.

A recipe is "ptest-enabled" if it inherits the `ptest` class.

#### 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 the `ptest` class: 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 host `make check` builds and runs on the same computer, while cross-compiling requires that the package is built on the host but executed for the target architecture (though often, as in the case for ptest, the execution occurs on the host). 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.

  Regardless, 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` 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.

## Working with Source Files

The OpenEmbedded build system works with source files located through the `SRC_URI` variable. When you build something using BitBake, a big part of the operation is locating and downloading all the source tarballs. For images, downloading all the source for various packages can take a significant amount of time.

This section presents information for working with source files that can lead to more efficient use of resources and time.

### Setting up Effective Mirrors

As mentioned, a good deal that goes into a Yocto Project build is simply downloading all of the source tarballs. Maybe you have been working with another build system (OpenEmbedded or Angstrom) for which you have built up a sizable directory of source tarballs. Or, perhaps someone else has such a directory for which you have read access. If so, you can save time by adding statements to your configuration file so that the build process checks local directories first for existing tarballs before checking the Internet.

Here is an efficient way to set it up in your `local.conf` file:

         SOURCE_MIRROR_URL ?= "file:///home/you/your-download-dir/"
         INHERIT += "own-mirrors"
         BB_GENERATE_MIRROR_TARBALLS = "1"
         # BB_NO_NETWORK = "1"

In the previous example, the `BB_GENERATE_MIRROR_TARBALLS` variable causes the OpenEmbedded build system to generate tarballs of the Git repositories and store them in the `DL_DIR` directory. Due to performance reasons, generating and storing these tarballs is not the build system's default behavior.

You can also use the `PREMIRRORS` variable. For an example, see the variable's glossary entry in the Yocto Project Reference Manual.

### Getting Source Files and Suppressing the Build

Another technique you can use to ready yourself for a successive string of build operations, is to pre-fetch all the source files without actually starting a build. This technique lets you work through any download issues and ultimately gathers all the source files into your download directory `build/downloads`, which is located with `DL_DIR`.

Use the following BitBake command form to fetch all the necessary sources without starting the build:

         $ bitbake -c fetchall target

This variation of the BitBake command guarantees that you have all the sources for that BitBake target should you disconnect from the Internet and want to do the build later offline.

## Building Software from an External Source

By default, the OpenEmbedded build system uses the Build Directory when building 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 the `externalsrc` class 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 = "path-to-your-source-tree"

This next example shows how to accomplish the same thing by setting `EXTERNALSRC` in the recipe itself or in the recipe's append file:

         EXTERNALSRC = "path"
         EXTERNALSRC_BUILD = "path"

In order for these settings to take effect, you must globally or locally inherit the `externalsrc` class.

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-your-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 these 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.

To remove initscripts from your image altogether, set this variable also:

         VIRTUAL-RUNTIME_initscripts = ""

For information on the backfill variable, see `DISTRO_FEATURES_BACKFILL_CONSIDERED`.

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

Set these 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.

## Selecting a Device Manager

The Yocto Project provides multiple ways to manage the device manager (`/dev`):

- Persistent and Pre-Populated`/dev`: For this case, the `/dev` directory is persistent and the required device nodes are created during the build.

- Use `devtmpfs` with a Device Manager: For this case, the `/dev` directory is provided by the kernel as an in-memory file system and is automatically populated by the kernel at runtime. Additional configuration of device nodes is done in user space by a device manager like `udev` or `busybox-mdev`.

### Using Persistent and Pre-Populated`/dev`

To use the static method for device population, you need to set the `USE_DEVFS` variable to "0" as follows:

         USE_DEVFS = "0"

The content of the resulting `/dev` directory is defined in a Device Table file. The `IMAGE_DEVICE_TABLES` variable defines the Device Table to use and should be set in the machine or distro configuration file. Alternatively, you can set this variable in your `local.conf` configuration file.

If you do not define the `IMAGE_DEVICE_TABLES` variable, the default `device_table-minimal.txt` is used:

         IMAGE_DEVICE_TABLES = "device_table-mymachine.txt"

The population is handled by the `makedevs` utility during image creation:

### Using `devtmpfs` and a Device Manager

To use the dynamic method for device population, you need to use (or be sure to set) the `USE_DEVFS` variable to "1", which is the default:

         USE_DEVFS = "1"

With this setting, the resulting `/dev` directory is populated by the kernel using `devtmpfs`. Make sure the corresponding kernel configuration variable `CONFIG_DEVTMPFS` is set when building you build a Linux kernel.

All devices created by `devtmpfs` will be owned by `root` and have permissions `0600`.

To have more control over the device nodes, you can use a device manager like `udev` or `busybox-mdev`. You choose the device manager by defining the `VIRTUAL-RUNTIME_dev_manager` variable in your machine or distro configuration file. Alternatively, you can set this variable in your `local.conf` configuration file:

         VIRTUAL-RUNTIME_dev_manager = "udev"

         # Some alternative values
         # VIRTUAL-RUNTIME_dev_manager = "busybox-mdev"
         # VIRTUAL-RUNTIME_dev_manager = "systemd"

## 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 packages that depend 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, the `PV` of the recipe needs to reference `SRCPV`. Here is an example:

         PV = "1.2.3+git${SRCPV}"

Then, you can add the following to your `local.conf`:

         SRCREV_pn-PN = "${AUTOREV}"

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

If you do not want to update your local configuration file, you can add the following directly to the recipe to finish enabling the feature:

         SRCREV = "${AUTOREV}"

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-opkg-native ?= "${AUTOREV}"
         #SRCREV_pn-opkg-sdk ?= "${AUTOREV}"
         #SRCREV_pn-opkg ?= "${AUTOREV}"
         #SRCREV_pn-opkg-utils-native ?= "${AUTOREV}"
         #SRCREV_pn-opkg-utils ?= "${AUTOREV}"
         SRCREV_pn-gconf-dbus ?= "${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-2 ?= "${AUTOREV}"
         SRCREV_pn-matchbox-themes-extra ?= "${AUTOREV}"
         SRCREV_pn-matchbox-terminal ?= "${AUTOREV}"
         SRCREV_pn-matchbox-wm ?= "${AUTOREV}"
         SRCREV_pn-settings-daemon ?= "${AUTOREV}"
         SRCREV_pn-screenshot ?= "${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 build-time checks 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 this 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` when the root filesystem is created. Furthermore, `$D` is blank when the script is run on the target device. This implies two purposes for `$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, which run on the host system, 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 `qemu` class.

### 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. You can run these tests on either QEMU or actual target hardware. 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

Depending on whether you are planning to run tests using QEMU or on the hardware, you have to take different steps to enable the tests. See the following subsections for information on how to enable both types of tests.

#### Enabling Runtime Tests on QEMU

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 an 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`.

- Be sure your host has the correct packages installed: Depending your host's distribution, you need to have the following packages installed:

  - Ubuntu and Debian: `sysstat` and `iproute2`

  - OpenSUSE: `sysstat` and `iproute2`

  - Fedora: `sysstat` and `iproute`

  - CentOS: `sysstat` and `iproute`

Once you start running the tests, the following happens:

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

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

3. 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.

4. 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`.

5. 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`.

6. 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`.

#### Enabling Runtime Tests on Hardware

The OpenEmbedded build system can run tests on real hardware, and for certain devices it can also deploy the image to be tested onto the device beforehand.

For automated deployment, a "master image" is installed onto the hardware once as part of setup. Then, each time tests are to be run, the following occurs:

1. The master image is booted into and used to write the image to be tested to a second partition.

2. The device is then rebooted using an external script that you need to provide.

3. The device boots into the image to be tested.

When running tests (independent of whether the image has been deployed automatically or not), the device is expected to be connected to a network on a pre-determined IP address. You can either use static IP addresses written into the image, or set the image to use DHCP and have your DHCP server on the test network assign a known IP address based on the MAC address of the device.

In order to run tests on hardware, you need to set `TEST_TARGET` to an appropriate value. For QEMU, you do not have to change anything, the default value is "QemuTarget". For running tests on hardware, the following options exist:

- "SimpleRemoteTarget": Choose "SimpleRemoteTarget" if you are going to run tests on a target system that is already running the image to be tested and is available on the network. You can use "SimpleRemoteTarget" in conjunction with either real hardware or an image running within a separately started QEMU or any other virtual machine manager.

- "Systemd-bootTarget": Choose "Systemd-bootTarget" if your hardware is an EFI-based machine with `systemd-boot` as bootloader and `core-image-testmaster` (or something similar) is installed. Also, your hardware under test must be in a DHCP-enabled network that gives it the same IP address for each reboot.

  If you choose "Systemd-bootTarget", there are additional requirements and considerations. See the "Selecting Systemd-bootTarget" section, which follows, for more information.

- "BeagleBoneTarget": Choose "BeagleBoneTarget" if you are deploying images and running tests on the BeagleBone "Black" or original "White" hardware. For information on how to use these tests, see the comments at the top of the BeagleBoneTarget `meta-yocto-bsp/lib/oeqa/controllers/beaglebonetarget.py` file.

- "EdgeRouterTarget": Choose "EdgeRouterTarget" is you are deploying images and running tests on the Ubiquiti Networks EdgeRouter Lite. For information on how to use these tests, see the comments at the top of the EdgeRouterTarget `meta-yocto-bsp/lib/oeqa/controllers/edgeroutertarget.py` file.

- "GrubTarget": Choose the "supports deploying images and running tests on any generic PC that boots using GRUB. For information on how to use these tests, see the comments at the top of the GrubTarget `meta-yocto-bsp/lib/oeqa/controllers/grubtarget.py` file.

- "your-target": Create your own custom target if you want to run tests when you are deploying images and running tests on a custom machine within your BSP layer. To do this, you need to add a Python unit that defines the target class under `lib/oeqa/controllers/` within your layer. You must also provide an empty `__init__.py`. For examples, see files in `meta-yocto-bsp/lib/oeqa/controllers/`.

#### Selecting Systemd-bootTarget

If you did not set `TEST_TARGET` to "Systemd-bootTarget", then you do not need any information in this section. You can skip down to the "Running Tests" section.

If you did set `TEST_TARGET` to "Systemd-bootTarget", you also need to perform a one-time setup of your master image by doing the following:

1. Set `EFI_PROVIDER`: Be sure that `EFI_PROVIDER` is as follows:

            EFI_PROVIDER = "systemd-boot"

2. Build the master image: Build the `core-image-testmaster` image. The `core-image-testmaster` recipe is provided as an example for a "master" image and you can customize the image recipe as you would any other recipe.

   Here are the image recipe requirements:

   - Inherits `core-image` so that kernel modules are installed.

   - Installs normal linux utilities not busybox ones (e.g. `bash`, `coreutils`, `tar`, `gzip`, and `kmod`).

   - Uses a custom Initial RAM Disk (initramfs) image with a custom installer. A normal image that you can install usually creates a single rootfs partition. This image uses another installer that creates a specific partition layout. Not all Board Support Packages (BSPs) can use an installer. For such cases, you need to manually create the following partition layout on the target:

     - First partition mounted under `/boot`, labeled "boot".

     - The main rootfs partition where this image gets installed, which is mounted under `/`.

     - Another partition labeled "testrootfs" where test images get deployed.

3. Install image: Install the image that you just built on the target system.

The final thing you need to do when setting `TEST_TARGET` to "Systemd-bootTarget" is to set up the test image:

1. Set up your `local.conf` file: Make sure you have the following statements in your `local.conf` file:

            IMAGE_FSTYPES += "tar.gz"
            INHERIT += "testimage"
            TEST_TARGET = "Systemd-bootTarget"
            TEST_TARGET_IP = "192.168.2.3"

2. Build your test image: Use BitBake to build the image:

            $ bitbake core-image-sato

#### Power Control

For most hardware targets other than SimpleRemoteTarget, you can control power:

- You can use `TEST_POWERCONTROL_CMD` together with `TEST_POWERCONTROL_EXTRA_ARGS` as a command that runs on the host and does power cycling. The test code passes one argument to that command: off, on or cycle (off then on). Here is an example that could appear in your `local.conf` file:

           TEST_POWERCONTROL_CMD = "powercontrol.exp test 10.11.12.1 nuc1"

  In this example, the expect script does the following:

           ssh test@10.11.12.1 "pyctl nuc1 arg"

  It then runs a Python script that controls power for a label called `nuc1`.

  You need to customize `TEST_POWERCONTROL_CMD` and `TEST_POWERCONTROL_EXTRA_ARGS` for your own setup. The one requirement is that it accepts "on", "off", and "cycle" as the last argument.

- When no command is defined, it connects to the device over SSH and uses the classic reboot command to reboot the device. Classic reboot is fine as long as the machine actually reboots (i.e. the SSH test has not failed). It is useful for scenarios where you have a simple setup, typically with a single board, and where some manual interaction is okay from time to time.

If you have no hardware to automatically perform power control but still wish to experiment with automated hardware testing, you can use the dialog-power-control script that shows a dialog prompting you to perform the required power action. This script requires either KDialog or Zenity to be installed. To use this script, set the `TEST_POWERCONTROL_CMD` variable as follows:

         TEST_POWERCONTROL_CMD = "${COREBASE}/scripts/contrib/dialog-power-control"

#### Serial Console Connection

For test target classes requiring a serial console to interact with the bootloader (e.g. BeagleBoneTarget, EdgeRouterTarget, and GrubTarget), you need to specify a command to use to connect to the serial console of the target machine by using the `TEST_SERIALCONTROL_CMD` variable and optionally the `TEST_SERIALCONTROL_EXTRA_ARGS` variable.

These cases could be a serial terminal program if the machine is connected to a local serial port, or a `telnet` or `ssh` command connecting to a remote console server. Regardless of the case, the command simply needs to connect to the serial console and forward that connection to standard input and output as any normal terminal program does. For example, to use the picocom terminal program on serial device `/dev/ttyUSB0` at 115200bps, you would set the variable as follows:

         TEST_SERIALCONTROL_CMD = "picocom /dev/ttyUSB0 -b 115200"

For local devices where the serial port device disappears when the device reboots, an additional "serdevtry" wrapper script is provided. To use this wrapper, simply prefix the terminal command with `${COREBASE}/scripts/contrib/serdevtry`:

         TEST_SERIALCONTROL_CMD = "${COREBASE}/scripts/contrib/serdevtry picocom -b
    115200 /dev/ttyUSB0"

### 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, 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 the `testimage` class by editing your `local.conf` file:

          INHERIT += "testimage"

  Next, use BitBake to run the tests:

           bitbake -c testimage image

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 and influences test dependencies. Consequently, tests that depend on other tests should be added after the test on which they depend. For example, since the `ssh` test 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.

### Exporting Tests

You can export tests so that they can run independently of the build system. Exporting tests is required if you want to be able to hand the test execution off to a scheduler. You can only export tests that are defined in `TEST_SUITES`.

If your image is already built, make sure the following are set in your `local.conf` file:

         INHERIT +="testexport"
         TEST_TARGET_IP = "IP-address-for-the-test-target"
         TEST_SERVER_IP = "IP-address-for-the-test-server"

You can then export the tests with the following BitBake command form:

         $ bitbake image -c testexport

Exporting the tests places them in the Build Directory in `tmp/testexport/`image, which is controlled by the `TEST_EXPORT_DIR` variable.

You can now run the tests outside of the build environment:

         $ cd tmp/testexport/image
         $ ./runexported.py testdata.json

Here is a complete example that shows IP addresses and uses the `core-image-sato` image:

         INHERIT +="testexport"
         TEST_TARGET_IP = "192.168.7.2"
         TEST_SERVER_IP = "192.168.7.1"

Use BitBake to export the tests:

         $ bitbake core-image-sato -c testexport

Run the tests outside of the build environment using the following:

         $ cd tmp/testexport/core-image-sato
         $ ./runexported.py testdata.json

### 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 the following:

- Filenames need to map directly to test (module) names.

- Do not use module names that collide with existing core tests.

- Minimally, an empty `__init__.py` file must exist in the runtime directory.

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 the manifest file that is generated during the `do_rootfs` task.

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

#### 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 test context, which gives access to the following attributes:

  - `d`: The BitBake datastore, 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.

  - `target`: The target controller object used to deploy and start an image on a particular target (e.g. QemuTarget, SimpleRemote, and Systemd-bootTarget). Tests usually use the following:

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

    - `server_ip`: The host's IP address, which is usually used by the "smart" test suite.

    - `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)`.

### Installing Packages in the DUT Without the Package Manager

When a test requires a package built by BitBake, it is possible to install that package. Installing the package does not require a package manager be installed in the device under test (DUT). It does, however, require an SSH connection and the target must be using the `sshcontrol` class.

This method uses `scp` to copy files from the host to the target, which causes permissions and special attributes to be lost.

A JSON file is used to define the packages needed by a test. This file must be in the same path as the file used to define the tests. Furthermore, the filename must map directly to the test module name with a `.json` extension.

The JSON file must include an object with the test name as keys of an object or an array. This object (or array of objects) uses the following data:

- "pkg" - A mandatory string that is the name of the package to be installed.

- "rm" - An optional boolean, which defaults to "false", that specifies to remove the package after the test.

- "extract" - An optional boolean, which defaults to "false", that specifies if the package must be extracted from the package format. When set to "true", the package is not automatically installed into the DUT.

Following is an example JSON file that handles test "foo" installing package "bar" and test "foobar" installing packages "foo" and "bar". Once the test is complete, the packages are removed from the DUT.

         {
             "foo": {
                 "pkg": "bar"
             },
             "foobar": [
                 {
                     "pkg": "foo",
                     "rm": true
                 },
                 {
                     "pkg": "bar",
                     "rm": true
                 }
             ]
         }

## 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 debug (`-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, you have 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 following steps show you how to debug using the GNU project debugger.

1. Configure your build system to construct the companion debug filesystem:

   In your `local.conf` file, set the following:

            IMAGE_GEN_DEBUGFS = "1"
            IMAGE_FSTYPES_DEBUGFS = "tar.bz2"

   These options cause the OpenEmbedded build system to generate a special companion filesystem fragment, which contains the matching source and debug symbols to your deployable filesystem. The build system does this by looking at what is in the deployed filesystem, and pulling the corresponding `-dbg` packages.

   The companion debug filesystem is not a complete filesystem, but only contains the debug fragments. This filesystem must be combined with the full filesystem for debugging. Subsequent steps in this procedure show how to combine the partial filesystem with the full filesystem.

2. Configure the system to include Gdbserver in the target filesystem:

   Make the following addition in either your `local.conf` file or in an image recipe:

            IMAGE_INSTALL_append = “ gdbserver"

   The change makes sure the `gdbserver` package is included.

3. Build the environment:

   Use the following command to construct the image and the companion Debug Filesystem:

            $ bitbake image

   Build the cross GDB component and make it available for debugging. Build the SDK that matches the image. Building the SDK is best for a production build that can be used later for debugging, especially during long term maintenance:

            $ bitbake -c populate_sdk image

   Alternatively, you can build the minimal toolchain components that match the target. Doing so creates a smaller than typical SDK and only contains a minimal set of components with which to build simple test applications, as well as run the debugger:

            $ bitbake meta-toolchain

   A final method is to build Gdb itself within the build system:

            $ bitbake gdb-cross-architecture

   Doing so produces a temporary copy of `cross-gdb` you can use for debugging during development. While this is the quickest approach, the two previous methods in this step are better when considering long-term maintenance strategies.

   If you run `bitbake gdb-cross`, the OpenEmbedded build system suggests the actual image (e.g. `gdb-cross-i586`). The suggestion is usually the actual name you want to use.

4. Set up the `debugfs`

   Run the following commands to set up the `debugfs`:

            $ mkdir debugfs
            $ cd debugfs
            $ tar xvfj build-dir/tmp-glibc/deploy/images/machine/image.rootfs.tar.bz2
            $ tar xvfj build-dir/tmp-glibc/deploy/images/machine/image-dbg.rootfs.tar.bz2

5. Set up GDB

   Install the SDK (if you built one) and then source the correct environment file. Sourcing the environment file puts the SDK in your `PATH` environment variable.

   If you are using the build system, Gdb is located in build-dir/tmp/sysroots/host/usr/bin/architecture/architecture-gdb

6. Boot the target:

   For information on how to run QEMU, see the QEMU Documentation.

   Be sure to verify that your host can access the target via TCP.

7. Debug a program:

   Debugging a program involves running Gdbserver on the target and then running Gdb on the host. The example in this step debugs `gzip`:

            root@qemux86:~# gdbserver localhost:1234 /bin/gzip —help

   For additional Gdbserver options, see the Gdb Server Documentation.

   After running Gdbserver on the target, you need to run Gdb on the host and configure it and connect to the target. Use these commands:

            $ cd directory-holding-the-debugfs-directory
            $ arch-gdb

            (gdb) set sysroot debugfs
            (gdb) set substitute-path /usr/src/debug debugfs/usr/src/debug
            (gdb) target remote IP-of-target:1234

   At this point, everything should automatically load (i.e. matching binaries, symbols and headers).

   The Gdb `set` commands in the previous example can be placed into the users `~/.gdbinit` file. Upon starting, Gdb automatically runs whatever commands are in that file.

8. Deploying without a full image rebuild:

   In many cases, during development you want a quick method to deploy a new binary to the target and debug it, without waiting for a full image build.

   One approach to solving this situation is to just build the component you want to debug. Once you have built the component, copy the executable directly to both the target and the host `debugfs`.

   If the binary is processed through the debug splitting in OpenEmbedded, you should also copy the debug items (i.e. `.debug` contents and corresponding `/usr/src/debug` files) from the work directory. Here is an example:

            $ bitbake bash
            $ bitbake -c devshell bash
            $ cd ..
            $ scp packages-split/bash/bin/bash target:/bin/bash
            $ cp -a packages-split/bash-dbg/* path/debugfs

## Debugging with the GNU Project Debugger (GDB) on the Target

The previous section addressed using GDB remotely for debugging purposes, which is the most usual case due to the inherent hardware limitations on many embedded devices. However, debugging in the target hardware itself is also possible with more powerful devices. This section describes what you need to do in order to support using GDB to debug on the target hardware.

To support this kind of debugging, you need do the following:

- Ensure that GDB is on the target. You can do this by adding "gdb" to `IMAGE_INSTALL`:

           IMAGE_INSTALL_append = " gdb"

  Alternatively, you can add "tools-debug" to `IMAGE_FEATURES`:

           IMAGE_FEATURES_append = " tools-debug"

- Ensure that debug symbols are present. You can make sure these symbols are present by installing `-dbg`:

           IMAGE_INSTALL_append = " packagename-dbg"

  Alternatively, you can do the following to include all the debug symbols:

           IMAGE_FEATURES_append = " dbg-pkgs"

To improve the debug information accuracy, you can reduce the level of optimization used by the compiler. For example, when adding the following line to your `local.conf` file, you will reduce optimization from `FULL_OPTIMIZATION` of "-O2" to `DEBUG_OPTIMIZATION` of "-O -fno-omit-frame-pointer":

         DEBUG_BUILD = "1"

Consider that this will reduce the application's performance and is recommended only for debugging purposes.

## Debugging Parallel Make Races

A parallel `make` race occurs when the build consists of several parts that are run simultaneously and a situation occurs when the output or result of one part is not ready for use with a different part of the build that depends on that output. Parallel make races are annoying and can sometimes be difficult to reproduce and fix. However, some simple tips and tricks exist that can help you debug and fix them. This section presents a real-world example of an error encountered on the Yocto Project autobuilder and the process used to fix it.

If you cannot properly fix a `make` race condition, you can work around it by clearing either the `PARALLEL_MAKE` or `PARALLEL_MAKEINST` variables.

### The Failure

For this example, assume that you are building an image that depends on the "neard" package. And, during the build, BitBake runs into problems and creates the following output.

This example log file has longer lines artificially broken to make the listing easier to read.

If you examine the output or the log file, you see the failure during `make`:

         | DEBUG: SITE files ['endian-little', 'bit-32', 'ix86-common', 'common-linux', 'common-glibc', 'i586-linux', 'common']
         | DEBUG: Executing shell function do_compile
         | NOTE: make -j 16
         | make --no-print-directory all-am
         | /bin/mkdir -p include/near
         | /bin/mkdir -p include/near
         | /bin/mkdir -p include/near
         | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
           0.14-r0/neard-0.14/include/types.h include/near/types.h
         | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
           0.14-r0/neard-0.14/include/log.h include/near/log.h
         | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
           0.14-r0/neard-0.14/include/plugin.h include/near/plugin.h
         | /bin/mkdir -p include/near
         | /bin/mkdir -p include/near
         | /bin/mkdir -p include/near
         | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
           0.14-r0/neard-0.14/include/tag.h include/near/tag.h
         | /bin/mkdir -p include/near
         | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
           0.14-r0/neard-0.14/include/adapter.h include/near/adapter.h
         | /bin/mkdir -p include/near
         | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
           0.14-r0/neard-0.14/include/ndef.h include/near/ndef.h
         | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
           0.14-r0/neard-0.14/include/tlv.h include/near/tlv.h
         | /bin/mkdir -p include/near
         | /bin/mkdir -p include/near
         | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
           0.14-r0/neard-0.14/include/setting.h include/near/setting.h
         | /bin/mkdir -p include/near
         | /bin/mkdir -p include/near
         | /bin/mkdir -p include/near
         | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
           0.14-r0/neard-0.14/include/device.h include/near/device.h
         | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
           0.14-r0/neard-0.14/include/nfc_copy.h include/near/nfc_copy.h
         | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
           0.14-r0/neard-0.14/include/snep.h include/near/snep.h
         | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
           0.14-r0/neard-0.14/include/version.h include/near/version.h
         | ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
           0.14-r0/neard-0.14/include/dbus.h include/near/dbus.h
         | ./src/genbuiltin nfctype1 nfctype2 nfctype3 nfctype4 p2p > src/builtin.h
         | i586-poky-linux-gcc  -m32 -march=i586 --sysroot=/home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/
           build/build/tmp/sysroots/qemux86 -DHAVE_CONFIG_H -I. -I./include -I./src -I./gdbus  -I/home/pokybuild/
           yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/sysroots/qemux86/usr/include/glib-2.0
           -I/home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/sysroots/qemux86/usr/
           lib/glib-2.0/include  -I/home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/
           tmp/sysroots/qemux86/usr/include/dbus-1.0 -I/home/pokybuild/yocto-autobuilder/yocto-slave/
           nightly-x86/build/build/tmp/sysroots/qemux86/usr/lib/dbus-1.0/include  -I/home/pokybuild/yocto-autobuilder/
           yocto-slave/nightly-x86/build/build/tmp/sysroots/qemux86/usr/include/libnl3
           -DNEAR_PLUGIN_BUILTIN -DPLUGINDIR=\""/usr/lib/near/plugins"\"
           -DCONFIGDIR=\""/etc/neard\"" -O2 -pipe -g -feliminate-unused-debug-types -c
           -o tools/snep-send.o tools/snep-send.c
         | In file included from tools/snep-send.c:16:0:
         | tools/../src/near.h:41:23: fatal error: near/dbus.h: No such file or directory
         |  #include <near/dbus.h>
         |                        ^
         | compilation terminated.
         | make[1]: *** [tools/snep-send.o] Error 1
         | make[1]: *** Waiting for unfinished jobs....
         | make: *** [all] Error 2
         | ERROR: oe_runmake failed

### Reproducing the Error

Because race conditions are intermittent, they do not manifest themselves every time you do the build. In fact, most times the build will complete without problems even though the potential race condition exists. Thus, once the error surfaces, you need a way to reproduce it.

In this example, compiling the "neard" package is causing the problem. So the first thing to do is build "neard" locally. Before you start the build, set the `PARALLEL_MAKE` variable in your `local.conf` file to a high number (e.g. "-j 20"). Using a high value for `PARALLEL_MAKE` increases the chances of the race condition showing up:

         $ bitbake neard

Once the local build for "neard" completes, start a `devshell` build:

         $ bitbake neard -c devshell

For information on how to use a `devshell`, see the "Using a Development Shell" section.

In the `devshell`, do the following:

         $ make clean
         $ make tools/snep-send.o

The `devshell` commands cause the failure to clearly be visible. In this case, a missing dependency exists for the "neard" Makefile target. Here is some abbreviated, sample output with the missing dependency clearly visible at the end:

         i586-poky-linux-gcc  -m32 -march=i586 --sysroot=/home/scott-lenovo/......
            .
            .
            .
         tools/snep-send.c
         In file included from tools/snep-send.c:16:0:
         tools/../src/near.h:41:23: fatal error: near/dbus.h: No such file or directory
          #include <near/dbus.h>
                           ^
         compilation terminated.
         make: *** [tools/snep-send.o] Error 1
         $

### Creating a Patch for the Fix

Because there is a missing dependency for the Makefile target, you need to patch the `Makefile.am` file, which is generated from `Makefile.in`. You can use Quilt to create the patch:

         $ quilt new parallelmake.patch
         Patch patches/parallelmake.patch is now on top
         $ quilt add Makefile.am
         File Makefile.am added to patch patches/parallelmake.patch

For more information on using Quilt, see the "Using Quilt in Your Workflow" section.

At this point you need to make the edits to `Makefile.am` to add the missing dependency. For our example, you have to add the following line to the file:

         tools/snep-send.$(OBJEXT): include/near/dbus.h

Once you have edited the file, use the `refresh` command to create the patch:

         $ quilt refresh
         Refreshed patch patches/parallelmake.patch

Once the patch file exists, you need to add it back to the originating recipe folder. Here is an example assuming a top-level Source Directory named `poky`:

         $ cp patches/parallelmake.patch poky/meta/recipes-connectivity/neard/neard

The final thing you need to do to implement the fix in the build is to update the "neard" recipe (i.e. `neard-0.14.bb`) so that the `SRC_URI` statement includes the patch file. The recipe file is in the folder above the patch. Here is what the edited `SRC_URI` statement would look like:

         SRC_URI = "${KERNELORG_MIRROR}/linux/network/nfc/${BPN}-${PV}.tar.xz \
                    file://neard.in \
                    file://neard.service.in \
                    file://parallelmake.patch \
                   "

With the patch complete and moved to the correct folder and the `SRC_URI` statement updated, you can exit the `devshell`:

         $ exit

### Testing the Build

With everything in place, you can get back to trying the build again locally:

         $ bitbake neard

This build should succeed.

Now you can open up a `devshell` again and repeat the clean and make operations as follows:

         $ bitbake neard -c devshell
         $ make clean
         $ make tools/snep-send.o

The build should work without issue.

As with all solved problems, if they originated upstream, you need to submit the fix for the recipe in OE-Core and upstream so that the problem is taken care of at its source. See the "How to Submit a Change" section for more information.

## 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, the requirements of the major FLOSS licenses can begin to be covered by assuming that three main areas of concern exist:

- 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.

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 source as a tarball. You can do this by adding the following to the `local.conf` file found in the Build Directory:

         INHERIT += "archiver"
         ARCHIVER_MODE[src] = "original"

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 us assume you are only concerned with GPL code as identified by running the following script:

         # Script to archive a subset of packages matching specific license(s)
         # Source and license files are copied into sub folders of package folder
         # Must be run from build folder
         #!/bin/bash
         src_release_dir="source-release"
         mkdir -p $src_release_dir
         for a in tmp/deploy/sources/*; do
            for d in $a/*; do
               # Get package name from path
               p=`basename $d`
               p=${p%-*}
               p=${p%-*}
               # Only archive GPL packages (update *GPL* regex for your license check)
               numfiles=`ls tmp/deploy/licenses/$p/*GPL* 2> /dev/null | wc -l`
               if [ $numfiles -gt 1 ]; then
                  echo Archiving $p
                  mkdir -p $src_release_dir/$p/source
                  cp $d/* $src_release_dir/$p/source 2> /dev/null
                  mkdir -p $src_release_dir/$p/license
                  cp tmp/deploy/licenses/$p/* $src_release_dir/$p/license 2> /dev/null
               fi
            done
         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"
         LICENSE_CREATE_PACKAGE = "1"

Adding these statements to the configuration file ensures that the licenses collected during package generation are included on your image.

Setting all three variables to "1" results in the image having two copies of the same license file. One copy resides in `/usr/share/common-licenses` and the other resides in `/usr/share/license`.

The reason for this behavior is because `COPY_LIC_DIRS` and `COPY_LIC_MANIFEST` add a copy of the license when the image is built but do not offer a path for adding licenses for newly installed packages to an image. `LICENSE_CREATE_PACKAGE` adds a separate package and an upgrade path for adding licenses to an 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 might 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_NO_CAP; branch of the poky repo
         $ git clone -b &DISTRO_NAME_NO_CAP; 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-poky/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-poky \
           ##OEROOT##/meta-yocto-bsp \
           ##OEROOT##/meta-mylayer \
           "

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.

## Using the Error Reporting Tool

The error reporting tool allows you to submit errors encountered during builds to a central database. Outside of the build environment, you can use a web interface to browse errors, view statistics, and query for errors. The tool works using a client-server system where the client portion is integrated with the installed Yocto Project Source Directory (e.g. `poky`). The server receives the information collected and saves it in a database.

A live instance of the error reporting server exists at . This server exists so that when you want to get help with build failures, you can submit all of the information on the failure easily and then point to the URL in your bug report or send an email to the mailing list.

If you send error reports to this server, the reports become publicly visible.

### Enabling and Using the Tool

By default, the error reporting tool is disabled. You can enable it by inheriting the `report-error` class by adding the following statement to the end of your `local.conf` file in your Build Directory.

         INHERIT += "report-error"

By default, the error reporting feature stores information in `${` `LOG_DIR` `}/error-report`. However, you can specify a directory to use by adding the following to your `local.conf` file:

         ERR_REPORT_DIR = "path"

Enabling error reporting causes the build process to collect the errors and store them in a file as previously described. When the build system encounters an error, it includes a command as part of the console output. You can run the command to send the error file to the server. For example, the following command sends the errors to an upstream server:

         $ send-error-report /home/brandusa/project/poky/build/tmp/log/error-report/error_report_201403141617.txt

In the previous example, the errors are sent to a public database available at , which is used by the entire community. If you specify a particular server, you can send the errors to a different database. Use the following command for more information on available options:

         $ send-error-report --help

When sending the error file, you are prompted to review the data being sent as well as to provide a name and optional email address. Once you satisfy these prompts, the command returns a link from the server that corresponds to your entry in the database. For example, here is a typical link:

         http://errors.yoctoproject.org/Errors/Details/9522/

Following the link takes you to a web interface where you can browse, query the errors, and view statistics.

### Disabling the Tool

To disable the error reporting feature, simply remove or comment out the following statement from the end of your `local.conf` file in your Build Directory.

         INHERIT += "report-error"

### Setting Up Your Own Error Reporting Server

If you want to set up your own error reporting server, you can obtain the code from the Git repository at . Instructions on how to set it up are in the README document.