# Source Directory Structure

The Source Directory consists of several components. Understanding them and knowing where they are located is key to using the Yocto Project well. This chapter describes the Source Directory and gives information about the various files and directories.

For information on how to establish a local Source Directory on your development system, see the "Locating Yocto Project Source Files" section in the Yocto Project Development Tasks Manual.

The OpenEmbedded build system does not support file or directory names that contain spaces. Be sure that the Source Directory you use does not contain these types of names.

## Top-Level Core Components

This section describes the top-level components of the Source Directory.

### `bitbake/`

This directory includes a copy of BitBake for ease of use. The copy usually matches the current stable BitBake release from the BitBake project. BitBake, a Metadata interpreter, reads the Yocto Project Metadata and runs the tasks defined by that data. Failures are usually from the Metadata and not from BitBake itself. Consequently, most users do not need to worry about BitBake.

When you run the `bitbake` command, the main BitBake executable, which resides in the `bitbake/bin/` directory, starts. Sourcing the environment setup script (i.e. `&OE_INIT_FILE;`) places the `scripts` and `bitbake/bin` directories (in that order) into the shell's `PATH` environment variable.

For more information on BitBake, see the BitBake User Manual.

### `build/`

This directory contains user configuration files and the output generated by the OpenEmbedded build system in its standard configuration where the source tree is combined with the output. The Build Directory is created initially when you `source` the OpenEmbedded build environment setup script (i.e. `&OE_INIT_FILE;`).

It is also possible to place output and configuration files in a directory separate from the Source Directory by providing a directory name when you `source` the setup script. For information on separating output from your local Source Directory files, see the "`&OE_INIT_FILE;`" section.

### `documentation/`

This directory holds the source for the Yocto Project documentation as well as templates and tools that allow you to generate PDF and HTML versions of the manuals. Each manual is contained in a sub-folder. For example, the files for this manual reside in the `ref-manual/` directory.

### `meta/`

This directory contains the OpenEmbedded-Core metadata. The directory holds recipes, common classes, and machine configuration for emulated targets (`qemux86`, `qemuarm`, and so forth.)

### `meta-poky/`

This directory contains the configuration for the Poky reference distribution.

### `meta-yocto-bsp/`

This directory contains the Yocto Project reference hardware Board Support Packages (BSPs). For more information on BSPs, see the Yocto Project Board Support Package (BSP) Developer's Guide.

### `meta-selftest/`

This directory adds additional recipes and append files used by the OpenEmbedded selftests to verify the behavior of the build system.

You do not have to add this layer to your `bblayers.conf` file unless you want to run the selftests.

### `meta-skeleton/`

This directory contains template recipes for BSP and kernel development.

### `scripts/`

This directory contains various integration scripts that implement extra functionality in the Yocto Project environment (e.g. QEMU scripts). The `&OE_INIT_FILE;` script appends this directory to the shell's `PATH` environment variable.

The `scripts` directory has useful scripts that assist in contributing back to the Yocto Project, such as `create-pull-request` and `send-pull-request`.

### `&OE_INIT_FILE;`

This script sets up the OpenEmbedded build environment. Running this script with the `source` command in a shell makes changes to `PATH` and sets other core BitBake variables based on the current working directory. You need to run an environment setup script before running BitBake commands. The script uses other scripts within the `scripts` directory to do the bulk of the work.

When you run this script, your Yocto Project environment is set up, a Build Directory is created, your working directory becomes the Build Directory, and you are presented with a list of common BitBake targets. Here is an example:

         $ source oe-init-build-env

         ### Shell environment set up for builds. ###

         You can now run 'bitbake <target>'

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

         You can also run generated qemu images with a command like 'runqemu qemux86'

The script gets its default list of common targets from the `conf-notes.txt` file, which is found in the `meta-poky` directory within the Source Directory. Should you have custom distributions, it is very easy to modify this configuration file to include your targets for your distribution. See the "Creating a Custom Template Configuration Directory" section in the Yocto Project Development Tasks Manual for more information.

By default, running this script without a Build Directory argument creates the `build` directory in your current working directory. If you provide a Build Directory argument when you `source` the script, you direct the OpenEmbedded build system to create a Build Directory of your choice. For example, the following command creates a Build Directory named `mybuilds` that is outside of the Source Directory:

         $ source &OE_INIT_FILE; ~/mybuilds

The OpenEmbedded build system uses the template configuration files, which are found by default in the `meta-poky/conf` directory in the Source Directory. See the "Creating a Custom Template Configuration Directory" section in the Yocto Project Development Tasks Manual for more information.
The OpenEmbedded build system does not support file or directory names that contain spaces. If you attempt to run the `&OE_INIT_FILE;` script from a Source Directory that contains spaces in either the filenames or directory names, the script returns an error indicating no such file or directory. Be sure to use a Source Directory free of names containing spaces.

### `LICENSE, README, and README.hardware`

These files are standard top-level files.

## The Build Directory - `build/`

The OpenEmbedded build system creates the Build Directory when you run the build environment setup scripts (i.e. `&OE_INIT_FILE;`).

If you do not give the Build Directory a specific name when you run a setup script, the name defaults to `build`.

The `TOPDIR` variable points to the Build Directory.

### `build/buildhistory`

The OpenEmbedded build system creates this directory when you enable the build history feature. The directory tracks build information into image, packages, and SDK subdirectories. For information on the build history feature, see the "Maintaining Build Output Quality" section in the Yocto Project Development Tasks Manual.

### `build/conf/local.conf`

This configuration file contains all the local user configurations for your build environment. The `local.conf` file contains documentation on the various configuration options. Any variable set here overrides any variable set elsewhere within the environment unless that variable is hard-coded within a file (e.g. by using '=' instead of '?='). Some variables are hard-coded for various reasons but these variables are relatively rare.

Edit this file to set the `MACHINE` for which you want to build, which package types you wish to use (`PACKAGE_CLASSES`), and the location from which you want to access downloaded files (`DL_DIR`).

If `local.conf` is not present when you start the build, the OpenEmbedded build system creates it from `local.conf.sample` when you `source` the top-level build environment setup script (i.e. `&OE_INIT_FILE;`).

The source `local.conf.sample` file used depends on the `$TEMPLATECONF` script variable, which defaults to `meta-poky/conf` when you are building from the Yocto Project development environment and defaults to `meta/conf` when you are building from the OpenEmbedded-Core environment. Because the script variable points to the source of the `local.conf.sample` file, this implies that you can configure your build environment from any layer by setting the variable in the top-level build environment setup script as follows:

         TEMPLATECONF=your_layer/conf

Once the build process gets the sample file, it uses `sed` to substitute final `${``OEROOT``}` values for all `##OEROOT##` values.
You can see how the `TEMPLATECONF` variable is used by looking at the `scripts/oe-setup-builddir` script in the Source Directory. You can find the Yocto Project version of the `local.conf.sample` file in the `meta-poky/conf` directory.

### `build/conf/bblayers.conf`

This configuration file defines layers, which are directory trees, traversed (or walked) by BitBake. The `bblayers.conf` file uses the `BBLAYERS` variable to list the layers BitBake tries to find.

If `bblayers.conf` is not present when you start the build, the OpenEmbedded build system creates it from `bblayers.conf.sample` when you `source` the top-level build environment setup script (i.e. `&OE_INIT_FILE;`).

The source `bblayers.conf.sample` file used depends on the `$TEMPLATECONF` script variable, which defaults to `meta-poky/conf` when you are building from the Yocto Project development environment and defaults to `meta/conf` when you are building from the OpenEmbedded-Core environment. Because the script variable points to the source of the `bblayers.conf.sample` file, this implies that you can base your build from any layer by setting the variable in the top-level build environment setup script as follows:

         TEMPLATECONF=your_layer/conf

Once the build process gets the sample file, it uses `sed` to substitute final `${``OEROOT``}` values for all `##OEROOT##` values.
You can see how the `TEMPLATECONF` variable `scripts/oe-setup-builddir` script in the Source Directory. You can find the Yocto Project version of the `bblayers.conf.sample` file in the `meta-poky/conf` directory.

### `build/conf/sanity_info`

This file indicates the state of the sanity checks and is created during the build.

### `build/downloads/`

This directory contains downloaded upstream source tarballs. You can reuse the directory for multiple builds or move the directory to another location. You can control the location of this directory through the `DL_DIR` variable.

### `build/sstate-cache/`

This directory contains the shared state cache. You can reuse the directory for multiple builds or move the directory to another location. You can control the location of this directory through the `SSTATE_DIR` variable.

### `build/tmp/`

The OpenEmbedded build system creates and uses this directory for all the build system's output. The `TMPDIR` variable points to this directory.

BitBake creates this directory if it does not exist. As a last resort, to clean up a build and start it from scratch (other than the downloads), you can remove everything in the `tmp` directory or get rid of the directory completely. If you do, you should also completely remove the `build/sstate-cache` directory.

### `build/tmp/buildstats/`

This directory stores the build statistics.

### `build/tmp/cache/`

When BitBake parses the metadata (recipes and configuration files), it caches the results in `build/tmp/cache/` to speed up future builds. The results are stored on a per-machine basis.

During subsequent builds, BitBake checks each recipe (together with, for example, any files included or appended to it) to see if they have been modified. Changes can be detected, for example, through file modification time (mtime) changes and hashing of file contents. If no changes to the file are detected, then the parsed result stored in the cache is reused. If the file has changed, it is reparsed.

### `build/tmp/deploy/`

This directory contains any "end result" output from the OpenEmbedded build process. The `DEPLOY_DIR` variable points to this directory. For more detail on the contents of the `deploy` directory, see the "Images" and "Application Development SDK" sections in the Yocto Project Overview and Concepts Manual.

### `build/tmp/deploy/deb/`

This directory receives any `.deb` packages produced by the build process. The packages are sorted into feeds for different architecture types.

### `build/tmp/deploy/rpm/`

This directory receives any `.rpm` packages produced by the build process. The packages are sorted into feeds for different architecture types.

### `build/tmp/deploy/ipk/`

This directory receives `.ipk` packages produced by the build process.

### `build/tmp/deploy/licenses/`

This directory receives package licensing information. For example, the directory contains sub-directories for `bash`, `busybox`, and `glibc` (among others) that in turn contain appropriate `COPYING` license files with other licensing information. For information on licensing, see the "Maintaining Open Source License Compliance During Your Product's Lifecycle" section in the Yocto Project Development Tasks Manual.

### `build/tmp/deploy/images/`

This directory receives complete filesystem images. If you want to flash the resulting image from a build onto a device, look here for the image.

Be careful when deleting files in this directory. You can safely delete old images from this directory (e.g. `core-image-*`). However, the kernel (`*zImage*`, `*uImage*`, etc.), bootloader and other supplementary files might be deployed here prior to building an image. Because these files are not directly produced from the image, if you delete them they will not be automatically re-created when you build the image again.

If you do accidentally delete files here, you will need to force them to be re-created. In order to do that, you will need to know the target that produced them. For example, these commands rebuild and re-create the kernel files:

         $ bitbake -c clean virtual/kernel
         $ bitbake virtual/kernel

### `build/tmp/deploy/sdk/`

The OpenEmbedded build system creates this directory to hold toolchain installer scripts, which when executed, install the sysroot that matches your target hardware. You can find out more about these installers in the "Building an SDK Installer" section in the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual.

### `build/tmp/sstate-control/`

The OpenEmbedded build system uses this directory for the shared state manifest files. The shared state code uses these files to record the files installed by each sstate task so that the files can be removed when cleaning the recipe or when a newer version is about to be installed. The build system also uses the manifests to detect and produce a warning when files from one task are overwriting those from another.

### `build/tmp/sysroots-components/`

This directory is the location of the sysroot contents that the task `do_prepare_recipe_sysroot` links or copies into the recipe-specific sysroot for each recipe listed in `DEPENDS`. Population of this directory is handled through shared state, while the path is specified by the `COMPONENTS_DIR` variable. Apart from a few unusual circumstances, handling of the `sysroots-components` directory should be automatic, and recipes should not directly reference `build/tmp/sysroots-components`.

### `build/tmp/sysroots/`

Previous versions of the OpenEmbedded build system used to create a global shared sysroot per machine along with a native sysroot. Beginning with the &DISTRO; version of the Yocto Project, sysroots exist in recipe-specific `WORKDIR` directories. Thus, the `build/tmp/sysroots/` directory is unused.

The `build/tmp/sysroots/` directory can still be populated using the `bitbake build-sysroots` command and can be used for compatibility in some cases. However, in general it is not recommended to populate this directory. Individual recipe-specific sysroots should be used.

### `build/tmp/stamps/`

This directory holds information that BitBake uses for accounting purposes to track what tasks have run and when they have run. The directory is sub-divided by architecture, package name, and version. Following is an example:

         stamps/all-poky-linux/distcc-config/1.0-r0.do_build-2fdd....2do

Although the files in the directory are empty of data, BitBake uses the filenames and timestamps for tracking purposes.

For information on how BitBake uses stamp files to determine if a task should be rerun, see the "Stamp Files and the Rerunning of Tasks" section in the Yocto Project Overview and Concepts Manual.

### `build/tmp/log/`

This directory contains general logs that are not otherwise placed using the package's `WORKDIR`. Examples of logs are the output from the `do_check_pkg` or `do_distro_check` tasks. Running a build does not necessarily mean this directory is created.

### `build/tmp/work/`

This directory contains architecture-specific work sub-directories for packages built by BitBake. All tasks execute from the appropriate work directory. For example, the source for a particular package is unpacked, patched, configured and compiled all within its own work directory. Within the work directory, organization is based on the package group and version for which the source is being compiled as defined by the `WORKDIR`.

It is worth considering the structure of a typical work directory. As an example, consider `linux-yocto-kernel-3.0` on the machine `qemux86` built within the Yocto Project. For this package, a work directory of `tmp/work/qemux86-poky-linux/linux-yocto/3.0+git1+<.....>`, referred to as the `WORKDIR`, is created. Within this directory, the source is unpacked to `linux-qemux86-standard-build` and then patched by Quilt. (See the "Using Quilt in Your Workflow" section in the Yocto Project Development Tasks Manual for more information.) Within the `linux-qemux86-standard-build` directory, standard Quilt directories `linux-3.0/patches` and `linux-3.0/.pc` are created, and standard Quilt commands can be used.

There are other directories generated within `WORKDIR`. The most important directory is `WORKDIR/temp/`, which has log files for each task (`log.do_*.pid`) and contains the scripts BitBake runs for each task (`run.do_*.pid`). The `WORKDIR/image/` directory is where "make install" places its output that is then split into sub-packages within `WORKDIR/packages-split/`.

### `build/tmp/work/tunearch/recipename/version/`

The recipe work directory - `${WORKDIR}`.

As described earlier in the "`build/tmp/sysroots/`" section, beginning with the &DISTRO; release of the Yocto Project, the OpenEmbedded build system builds each recipe in its own work directory (i.e. `WORKDIR`). The path to the work directory is constructed using the architecture of the given build (e.g. `TUNE_PKGARCH`, `MACHINE_ARCH`, or "allarch"), the recipe name, and the version of the recipe (i.e. `PE``:``PV``-``PR`).

A number of key subdirectories exist within each recipe work directory:

- `${WORKDIR}/temp`: Contains the log files of each task executed for this recipe, the "run" files for each executed task, which contain the code run, and a `log.task_order` file, which lists the order in which tasks were executed.

- `${WORKDIR}/image`: Contains the output of the `do_install` task, which corresponds to the `${``D``}` variable in that task.

- `${WORKDIR}/pseudo`: Contains the pseudo database and log for any tasks executed under pseudo for the recipe.

- `${WORKDIR}/sysroot-destdir`: Contains the output of the `do_populate_sysroot` task.

- `${WORKDIR}/package`: Contains the output of the `do_package` task before the output is split into individual packages.

- `${WORKDIR}/packages-split`: Contains the output of the `do_package` task after the output has been split into individual packages. Subdirectories exist for each individual package created by the recipe.

- `${WORKDIR}/recipe-sysroot`: A directory populated with the target dependencies of the recipe. This directory looks like the target filesystem and contains libraries that the recipe might need to link against (e.g. the C library).

- `${WORKDIR}/recipe-sysroot-native`: A directory populated with the native dependencies of the recipe. This directory contains the tools the recipe needs to build (e.g. the compiler, Autoconf, libtool, and so forth).

- `${WORKDIR}/build`: This subdirectory applies only to recipes that support builds where the source is separate from the build artifacts. The OpenEmbedded build system uses this directory as a separate build directory (i.e. `${``B``}`).

### `build/tmp/work-shared/`

For efficiency, the OpenEmbedded build system creates and uses this directory to hold recipes that share a work directory with other recipes. In practice, this is only used for `gcc` and its variants (e.g. `gcc-cross`, `libgcc`, `gcc-runtime`, and so forth).

## The Metadata - `meta/`

As mentioned previously, Metadata is the core of the Yocto Project. Metadata has several important subdivisions:

### `meta/classes/`

This directory contains the `*.bbclass` files. Class files are used to abstract common code so it can be reused by multiple packages. Every package inherits the `base.bbclass` file. Examples of other important classes are `autotools.bbclass`, which in theory allows any Autotool-enabled package to work with the Yocto Project with minimal effort. Another example is `kernel.bbclass` that contains common code and functions for working with the Linux kernel. Functions like image generation or packaging also have their specific class files such as `image.bbclass`, `rootfs_*.bbclass` and `package*.bbclass`.

For reference information on classes, see the "Classes" chapter.

### `meta/conf/`

This directory contains the core set of configuration files that start from `bitbake.conf` and from which all other configuration files are included. See the include statements at the end of the `bitbake.conf` file and you will note that even `local.conf` is loaded from there. While `bitbake.conf` sets up the defaults, you can often override these by using the (`local.conf`) file, machine file or the distribution configuration file.

### `meta/conf/machine/`

This directory contains all the machine configuration files. If you set `MACHINE = "qemux86"`, the OpenEmbedded build system looks for a `qemux86.conf` file in this directory. The `include` directory contains various data common to multiple machines. If you want to add support for a new machine to the Yocto Project, look in this directory.

### `meta/conf/distro/`

The contents of this directory controls any distribution-specific configurations. For the Yocto Project, the `defaultsetup.conf` is the main file here. This directory includes the versions and the `SRCDATE` definitions for applications that are configured here. An example of an alternative configuration might be `poky-bleeding.conf`. Although this file mainly inherits its configuration from Poky.

### `meta/conf/machine-sdk/`

The OpenEmbedded build system searches this directory for configuration files that correspond to the value of `SDKMACHINE`. By default, 32-bit and 64-bit x86 files ship with the Yocto Project that support some SDK hosts. However, it is possible to extend that support to other SDK hosts by adding additional configuration files in this subdirectory within another layer.

### `meta/files/`

This directory contains common license files and several text files used by the build system. The text files contain minimal device information and lists of files and directories with known permissions.

### `meta/lib/`

This directory contains OpenEmbedded Python library code used during the build process.

### `meta/recipes-bsp/`

This directory contains anything linking to specific hardware or hardware configuration information such as "u-boot" and "grub".

### `meta/recipes-connectivity/`

This directory contains libraries and applications related to communication with other devices.

### `meta/recipes-core/`

This directory contains what is needed to build a basic working Linux image including commonly used dependencies.

### `meta/recipes-devtools/`

This directory contains tools that are primarily used by the build system. The tools, however, can also be used on targets.

### `meta/recipes-extended/`

This directory contains non-essential applications that add features compared to the alternatives in core. You might need this directory for full tool functionality or for Linux Standard Base (LSB) compliance.

### `meta/recipes-gnome/`

This directory contains all things related to the GTK+ application framework.

### `meta/recipes-graphics/`

This directory contains X and other graphically related system libraries

### `meta/recipes-kernel/`

This directory contains the kernel and generic applications and libraries that have strong kernel dependencies.

### `meta/recipes-lsb4/`

This directory contains recipes specifically added to support the Linux Standard Base (LSB) version 4.x.

### `meta/recipes-multimedia/`

This directory contains codecs and support utilities for audio, images and video.

### `meta/recipes-rt/`

This directory contains package and image recipes for using and testing the `PREEMPT_RT` kernel.

### `meta/recipes-sato/`

This directory contains the Sato demo/reference UI/UX and its associated applications and configuration data.

### `meta/recipes-support/`

This directory contains recipes used by other recipes, but that are not directly included in images (i.e. dependencies of other recipes).

### `meta/site/`

This directory contains a list of cached results for various architectures. Because certain "autoconf" test results cannot be determined when cross-compiling due to the tests not able to run on a live system, the information in this directory is passed to "autoconf" for the various architectures.

### `meta/recipes.txt`

This file is a description of the contents of `recipes-*`.