# Introduction

This manual provides reference information for the current release of the Yocto Project. The Yocto Project is an open-source collaboration project focused on embedded Linux developers. Amongst other things, the Yocto Project uses the OpenEmbedded build system, which is based on the Poky project, to construct complete Linux images. You can find complete introductory and getting started information on the Yocto Project by reading the Yocto Project Quick Start. For task-based information using the Yocto Project, see the Yocto Project Development Manual and the Yocto Project Linux Kernel Development Manual. For Board Support Package (BSP) structure information, see the Yocto Project Board Support Package (BSP) Developer's Guide. You can find information on tracing and profiling in the Yocto Project Profiling and Tracing Manual. For information on BitBake, which is the task execution tool the OpenEmbedded build system is based on, see the BitBake User Manual. Finally, you can also find lots of Yocto Project information on the Yocto Project website.

## Documentation Overview

This reference manual consists of the following:

- Using the Yocto Project: Provides an overview of the components that make up the Yocto Project followed by information about debugging images created in the Yocto Project.

- A Closer Look at the Yocto Project Development Environment: Provides a more detailed look at the Yocto Project development environment within the context of development.

- Technical Details: Describes fundamental Yocto Project components as well as an explanation behind how the Yocto Project uses shared state (sstate) cache to speed build time.

- Migrating to a Newer Yocto Project Release: Describes release-specific information that helps you move from one Yocto Project Release to another.

- Directory Structure: Describes the Source Directory created either by unpacking a released Yocto Project tarball on your host development system, or by cloning the upstream Poky Git repository.

- Classes: Describes the classes used in the Yocto Project.

- Tasks: Describes the tasks defined by the OpenEmbedded build system.

- QA Error and Warning Messages: Lists and describes QA warning and error messages.

- Images: Describes the standard images that the Yocto Project supports.

- Features: Describes mechanisms for creating distribution, machine, and image features during the build process using the OpenEmbedded build system.

- Variables Glossary: Presents most variables used by the OpenEmbedded build system, which uses BitBake. Entries describe the function of the variable and how to apply them.

- Variable Context: Provides variable locality or context.

- FAQ: Provides answers for commonly asked questions in the Yocto Project development environment.

- Contributing to the Yocto Project: Provides guidance on how you can contribute back to the Yocto Project.

## System Requirements

For general Yocto Project system requirements, see the "What You Need and How You Get It" section in the Yocto Project Quick Start. The remainder of this section provides details on system requirements not covered in the Yocto Project Quick Start.

### Supported Linux Distributions

Currently, the Yocto Project is supported on the following distributions:

Yocto Project releases are tested against the stable Linux distributions in the following list. The Yocto Project should work on other distributions but validation is not performed against them.

In particular, the Yocto Project does not support and currently has no plans to support rolling-releases or development distributions due to their constantly changing nature. We welcome patches and bug reports, but keep in mind that our priority is on the supported platforms listed below.

If you encounter problems, please go to Yocto Project Bugzilla and submit a bug. We are interested in hearing about your experience.

- Ubuntu 14.04 (LTS)

- Ubuntu 14.10

- Fedora release 21

- CentOS release 6.x

- CentOS release 7.x

- Debian GNU/Linux 7.x (Wheezy)

- Debian GNU/Linux 8.x (Jessie)

- openSUSE 13.2

While the Yocto Project Team attempts to ensure all Yocto Project releases are one hundred percent compatible with each officially supported Linux distribution, instances might exist where you encounter a problem while using the Yocto Project on a specific distribution. For example, the CentOS 6.4 distribution does not include the Gtk+ 2.20.0 and PyGtk 2.21.0 (or higher) packages, which are required to run Hob.

### Required Packages for the Host Development System

The list of packages you need on the host development system can be large when covering all build scenarios using the Yocto Project. This section provides required packages according to Linux distribution and function.

#### Ubuntu and Debian

The following list shows the required packages by function given a supported Ubuntu or Debian Linux distribution:

- Essentials: Packages needed to build an image on a headless system:

           $ sudo apt-get install &UBUNTU_HOST_PACKAGES_ESSENTIAL;

- Graphical and Eclipse Plug-In Extras: Packages recommended if the host system has graphics support or if you are going to use the Eclipse IDE:

           $ sudo apt-get install libsdl1.2-dev xterm

- Documentation: Packages needed if you are going to build out the Yocto Project documentation manuals:

           $ sudo apt-get install make xsltproc docbook-utils fop dblatex xmlto

- ADT Installer Extras: Packages needed if you are going to be using the Application Development Toolkit (ADT) Installer:

           $ sudo apt-get install autoconf automake libtool libglib2.0-dev

#### Fedora Packages

The following list shows the required packages by function given a supported Fedora Linux distribution:

- Essentials: Packages needed to build an image for a headless system:

           $ sudo yum install &FEDORA_HOST_PACKAGES_ESSENTIAL;

- Graphical and Eclipse Plug-In Extras: Packages recommended if the host system has graphics support or if you are going to use the Eclipse IDE:

           $ sudo yum install SDL-devel xterm perl-Thread-Queue

- Documentation: Packages needed if you are going to build out the Yocto Project documentation manuals:

           $ sudo yum install make docbook-style-dsssl docbook-style-xsl \
           docbook-dtds docbook-utils fop libxslt dblatex xmlto xsltproc

- ADT Installer Extras: Packages needed if you are going to be using the Application Development Toolkit (ADT) Installer:

           $ sudo yum install autoconf automake libtool glib2-devel

#### openSUSE Packages

The following list shows the required packages by function given a supported openSUSE Linux distribution:

- Essentials: Packages needed to build an image for a headless system:

           $ sudo zypper install &OPENSUSE_HOST_PACKAGES_ESSENTIAL;

- Graphical and Eclipse Plug-In Extras: Packages recommended if the host system has graphics support or if you are going to use the Eclipse IDE:

           $ sudo zypper install libSDL-devel xterm

- Documentation: Packages needed if you are going to build out the Yocto Project documentation manuals:

           $ sudo zypper install make fop xsltproc dblatex xmlto

- ADT Installer Extras: Packages needed if you are going to be using the Application Development Toolkit (ADT) Installer:

           $ sudo zypper install autoconf automake libtool glib2-devel

#### CentOS Packages

The following list shows the required packages by function given a supported CentOS Linux distribution:

For CentOS 6.x, some of the versions of the components provided by the distribution are too old (e.g. Git, Python, and tar). It is recommended that you install the buildtools in order to provide versions that will work with the OpenEmbedded build system. For information on how to install the buildtools tarball, see the "Required Git, Tar, and Python Versions" section.

- Essentials: Packages needed to build an image for a headless system:

           $ sudo yum install &CENTOS_HOST_PACKAGES_ESSENTIAL;

- Graphical and Eclipse Plug-In Extras: Packages recommended if the host system has graphics support or if you are going to use the Eclipse IDE:

           $ sudo yum install SDL-devel xterm

- Documentation: Packages needed if you are going to build out the Yocto Project documentation manuals:

           $ sudo yum install make docbook-style-dsssl docbook-style-xsl \
           docbook-dtds docbook-utils fop libxslt dblatex xmlto xsltproc

- ADT Installer Extras: Packages needed if you are going to be using the Application Development Toolkit (ADT) Installer:

           $ sudo yum install autoconf automake libtool glib2-devel

### Required Git, tar, and Python Versions

In order to use the build system, your host development system must meet the following version requirements for Git, tar, and Python:

- Git 1.7.8 or greater

- tar 1.24 or greater

- Python 2.7.3 or greater not including Python 3.x, which is not supported.

If your host development system does not meet all these requirements, you can resolve this by installing a `buildtools` tarball that contains these tools. You can get the tarball one of two ways: download a pre-built tarball or use BitBake to build the tarball.

#### Downloading a Pre-Built `buildtools` Tarball

Downloading and running a pre-built buildtools installer is the easiest of the two methods by which you can get these tools:

1. Locate and download the `*.sh` at .

2. Execute the installation script. Here is an example:

            $ sh poky-glibc-x86_64-buildtools-tarball-x86_64-buildtools-nativesdk-standalone-&DISTRO;.sh

   During execution, a prompt appears that allows you to choose the installation directory. For example, you could choose the following:

            /home/your-username/buildtools

3. Source the tools environment setup script by using a command like the following:

            $ source /home/your_username/buildtools/environment-setup-i586-poky-linux

   Of course, you need to supply your installation directory and be sure to use the right file (i.e. i585 or x86-64).

   After you have sourced the setup script, the tools are added to `PATH` and any other environment variables required to run the tools are initialized. The results are working versions versions of Git, tar, Python and `chrpath`.

#### Building Your Own `buildtools` Tarball

Building and running your own buildtools installer applies only when you have a build host that can already run BitBake. In this case, you use that machine to build the `.sh` file and then take steps to transfer and run it on a machine that does not meet the minimal Git, tar, and Python requirements.

Here are the steps to take to build and run your own buildtools installer:

1. On the machine that is able to run BitBake, be sure you have set up your build environment with the setup script (`&OE_INIT_FILE;` or `oe-init-build-env-memres`).

2. Run the BitBake command to build the tarball:

            $ bitbake buildtools-tarball

   The `SDKMACHINE` variable in your `local.conf` file determines whether you build tools for a 32-bit or 64-bit system.
   Once the build completes, you can find the `.sh` file that installs the tools in the `tmp/deploy/sdk` subdirectory of the Build Directory. The installer file has the string "buildtools" in the name.

3. Transfer the `.sh` file from the build host to the machine that does not meet the Git, tar, or Python requirements.

4. On the machine that does not meet the requirements, run the `.sh` file to install the tools. Here is an example:

            $ sh poky-glibc-x86_64-buildtools-tarball-x86_64-buildtools-nativesdk-standalone-&DISTRO;.sh

   During execution, a prompt appears that allows you to choose the installation directory. For example, you could choose the following:

            /home/your_username/buildtools

5. Source the tools environment setup script by using a command like the following:

            $ source /home/your_username/buildtools/environment-setup-i586-poky-linux

   Of course, you need to supply your installation directory and be sure to use the right file (i.e. i585 or x86-64).

   After you have sourced the setup script, the tools are added to `PATH` and any other environment variables required to run the tools are initialized. The results are working versions versions of Git, tar, Python and `chrpath`.

## Obtaining the Yocto Project

The Yocto Project development team makes the Yocto Project available through a number of methods:

- Source Repositories: Working from a copy of the upstream `poky` repository is the preferred method for obtaining and using a Yocto Project release. You can view the Yocto Project Source Repositories at . In particular, you can find the `poky` repository at .

- Releases: Stable, tested releases are available as tarballs through .

- Nightly Builds: These tarball releases are available at . These builds include Yocto Project releases, meta-toolchain tarball installation scripts, and experimental builds.

- Yocto Project Website: You can find tarball releases of the Yocto Project and supported BSPs at the Yocto Project website. Along with these downloads, you can find lots of other information at this site.

## Development Checkouts

Development using the Yocto Project requires a local Source Directory. You can set up the Source Directory by cloning a copy of the upstream poky Git repository. For information on how to do this, see the "Getting Set Up" section in the Yocto Project Development Manual.