# 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 "Getting Set Up" section in the Yocto Project Development Manual.

## Top level core components

### `bitbake/`

The Source 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 wrapper script in `scripts/` is executed to run the main BitBake executable, which resides in the `bitbake/bin/` directory. Sourcing the &OE_INIT_FILE; script 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 documentation inculded in the `bitbake/doc/manual` directory of the Source Directory.

### `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 `&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 &OE_INIT_FILE;.

### `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 `poky-ref-manual`.

### `meta/`

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

### `meta-yocto/`

This directory contains the configuration for the Poky reference distribution.

### `meta-yocto-bsp/`

This directory contains the Yocto Project reference hardware BSPs.

### `meta-hob/`

This directory contains template recipes used by the Hob build UI.

### `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 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 this script before running BitBake commands. The script uses other scripts within the `scripts` directory to do the bulk of the work.

By default, running this script without a Build Directory argument creates the `build` directory. If you provide a Build Directory argument when you `source` the script, you direct 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

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

These files are standard top-level files.

## The Build Directory - `build/`

### `build/pseudodone`

This tag file indicates that the initial pseudo binary was created. The file is built the first time BitBake is invoked.

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

This file contains all the local user configuration for your build environment. If there is no `local.conf` present, it is created from `local.conf.sample`. 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`), where you want to downloaded files (`DL_DIR`), and how you want your host machine to use resources (`BB_NUMBER_THREADS` and `PARALLEL_MAKE`).

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

This file defines layers, which is a directory tree, traversed (or walked) by BitBake. If `bblayers.conf` is not present, it is created from `bblayers.conf.sample` when you `source` the environment setup script.

### `build/conf/sanity_info`

This file is created during the build to indicate the state of the sanity checks.

### `build/downloads/`

This directory is used for the upstream source tarballs. The directory can be reused by multiple builds or moved to another location. You can control the location of this directory through the `DL_DIR` variable.

### `build/sstate-cache/`

This directory is used for the shared state cache. The directory can be reused by multiple builds or moved to another location. You can control the location of this directory through the `SSTATE_DIR` variable.

### `build/tmp/`

This directory receives all the OpenEmbedded build system's output. 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 as well.

### `build/tmp/buildstats/`

This directory stores the build statistics.

### `build/tmp/cache/`

When BitBake parses the metadata, it creates a cache file of the result that can be used when subsequently running commands. These results are stored here on a per-machine basis.

### `build/tmp/deploy/`

This directory contains any 'end result' output from the OpenEmbedded build process.

### `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/licenses/`

This directory receives package licensing information. For example, the directory contains sub-directories for `bash`, `busybox`, and `eglibc` (among others) that in turn contain appropriate `COPYING` license files with other licensing information.

### `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-*`, `hob-image-*`, etc.). However, the kernel (`*zImage*`, `*uImage*`, etc.), bootloader and other supplementary files might be deployed here prior to building an image. Because these files, however, 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/ipk/`

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

### `build/tmp/sysroots/`

This directory contains shared header files and libraries as well as other shared data. Packages that need to share output with other packages do so within this directory. The directory is subdivided by architecture so multiple builds can run within the one Build Directory.

### `build/tmp/stamps/`

This directory holds information that that BitBake uses for accounting purposes to track what tasks have run and when they have run. The directory is sub-divided by architecture. The files in the directory are empty of data. However, BitBake uses the filenames and timestamps for tracking purposes.

### `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 `check_pkg` or `distro_check` tasks. Running a build does not necessarily mean this directory is created.

### `build/tmp/pkgdata/`

This directory contains intermediate packaging data that is used later in the packaging process. For more information, see the "Packaging - package*.bbclass" section.

### `build/tmp/work/`

This directory contains architecture-specific work sub-directories for packages built by BitBake. All tasks execute from a 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 for which the source is being compiled.

It is worth considering the structure of a typical work directory. As an example, consider the `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 `WORKDIR`, is created. Within this directory, the source is unpacked to `linux-qemux86-standard-build` and then patched by Quilt (see the "Modifying Package Source Code with Quilt" section in the Yocto Project Development Manual. 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/`.

## 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`.

### `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 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/`

Any distribution-specific configuration is controlled from this directory. 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/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-multimedia/`

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

### `meta/recipes-qt/`

This directory contains all things related to the Qt application framework.

### `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 that 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-*`.