User Guide

Dependencies & installation

This projects depends on

  • Python 3
  • distro Python 3 package
  • jsonschema Python 3 package
  • PyYAML Python 3 package (optional, for yaml file support)

If you need Python 2 support consider sending patches. The most obvious place to start is to use the trollius package intead of asyncio.

To install kas into your python site-package repository, run:

$ sudo pip3 install .


There are three options for using kas:

  • Install it locally via pip to get the kas command.
  • Use the docker image. In this case, run the commands in the examples below within docker run -it kasproject/kas:<version> sh or bind-mount the project into the container. See for all available images.
  • Use the run-kas wrapper from this directory. In this case replace kas in the examples below with path/to/run-kas.

Start build:

$ kas build /path/to/kas-project.yml

Alternatively, experienced bitbake users can invoke usual bitbake steps manually, e.g.:

$ kas shell /path/to/kas-project.yml -c 'bitbake dosfsutils-native'

kas will place downloads and build artifacts under the current directory when being invoked. You can specify a different location via the environment variable KAS_WORK_DIR.

Command line usage

Environment variables

Environment variables Description
KAS_WORK_DIR The path of the kas work directory, current work directory is the default.
KAS_REPO_REF_DIR The path to the repository reference directory. Repositories in this directory are used as references when cloning. In order for kas to find those repositories, they have to be named in a specific way. The repo URLs are translated like this: “” resolves to the name “”.
KAS_DISTRO KAS_MACHINE KAS_TARGET KAS_TASK This overwrites the respective setting in the configuration file.
SSH_PRIVATE_KEY Path to the private key file that should be added to an internal ssh-agent. This key cannot be password protected. This setting is useful for CI build servers. On desktop machines, an ssh-agent running outside the kas environment is more useful.
SSH_AGENT_PID SSH_AUTH_SOCK SSH agent process id and authentication socket. Used for cloning over SSH (alternative to SSH_PRIVATE_KEY).
DL_DIR SSTATE_DIR TMPDIR Environment variables that are transferred to the bitbake environment.
http_proxy https_proxy ftp_proxy no_proxy This overwrites the proxy configuration in the configuration file.
GIT_PROXY_COMMAND NO_PROXY Set proxy for native git fetches. NO_PROXY is evaluated by OpenEmbedded’s oe-git-proxy script.
SHELL The shell to start when using the shell plugin.
TERM The terminal options used in the shell plugin.

Use Cases

  1. Initial build/setup:

    $ mkdir $PROJECT_DIR
    $ cd $PROJECT_DIR
    $ git clone $PROJECT_URL meta-project
    $ kas build meta-project/kas-project.yml
  2. Update/rebuild:

    $ cd $PROJECT_DIR/meta-project
    $ git pull
    $ kas build kas-project.yml

Project Configuration

Currently JSON and YAML is supported as the base file format. Since YAML is arguable easier to read, this documentation focuses on the YAML format.

# Every file needs to contain a header, that provides kas with information
# about the context of this file.
  # The `version` entry in the header describes for which configuration
  # format version this file was created for. It is used by kas to figure
  # out if it is compatible with this file. The version is an integer that
  # is increased on every format change.
  version: x
# The machine as it is written into the `local.conf` of bitbake.
machine: qemu
# The distro name as it is written into the `local.conf` of bitbake.
distro: poky
  # This entry includes the repository where the config file is located
  # to the bblayers.conf:
  # Here we include a list of layers from the poky repository to the
  # bblayers.conf:
    url: ""
    refspec: 89e6c98d92887913cadf06b2adb97f26cde4849b

A minimal input file consist out of the header, machine, distro, and repos.

Additionally, you can add bblayers_conf_header and local_conf_header which are strings that are added to the head of the respective files (bblayers.conf or local.conf):

  meta-custom: |
    BBPATH = "${TOPDIR}"
    BBFILES ?= ""
  meta-custom: |
    PATCHRESOLVE = "noop"
    CONF_VERSION = "1"
    IMAGE_FSTYPES = "tar"

meta-custom in these examples should be a unique name (in project scope) for this configuration entries. We assume that your configuration file is part of a meta-custom repository/layer. This way its possible to overwrite or append entries in files that include this configuration by naming an entry the same (overwriting) or using a unused name (appending).

Including in-tree configuration files

Its currently possible to include kas configuration files from the same repository/layer like this:

  version: x
    - base.yml
    - bsp.yml
    - product.yml

The specified files are addressed relative to your current configuration file.

Including configuration files from other repos

Its also possible to include configuration files from other repos like this:

  version: x
    - repo: poky
      file: kas-poky.yml
    - repo: meta-bsp-collection
      file: hw1/kas-hw-bsp1.yml
    - repo: meta-custom
      file: products/product.yml
    url: ""
    refspec: 3f786850e387550fdab836ed7e6dc881de23001b
      # Additional to the layers that are added from this repository
      # in the hw1/kas-hw-bsp1.yml, we add here an additional bsp
      # meta layer:
    url: ""
    refspec: 89e6c98d92887913cadf06b2adb97f26cde4849b
      # If `kas-poky.yml` adds the `meta-yocto-bsp` layer and we
      # do not want it in our bblayers for this project, we can
      # overwrite it by setting:
      meta-yocto-bsp: exclude

The files are addressed relative to the git repository path.

The include mechanism collects and merges the content from top to buttom and depth first. That means that settings in one include file are overwritten by settings in a latter include file and entries from the last include file can be overwritten by the current file. While merging all the dictionaries are merged recursive while preserving the order in which the entries are added to the dictionary. This means that local_conf_header entries are added to the local.conf file in the same order in which they are defined in the different include files. Note that the order of the configuration file entries is not preserved within one include file, because the parser creates normal unordered dictionaries.

Including configuration files via the command line

When specifying the kas configuration file on the command line, additional configurations can be included ad-hoc:

$ kas build kas-base.yml:debug-image.yml:board.yml

This is equivalent to static inclusion from some kas-combined.yml like this:

  version: x
    - kas-base.yml
    - debug.image.yml
    - board.yml

Command line inclusion allows to create configurations on-demand, without the need to write a kas configuration file for each possible combination.

Note that all configuration files combined via the command line either have to come from the same repository or have to live outside of any versioning control. kas will refuse any other combination in order to avoid complications and configuration flaws that can easily emerge from them.

Configuration reference

  • header: dict [required]

    The header of every kas configuration file. It contains information about context of the file.

    • version: integer [required]

      Lets kas check if it is compatible with this file. See the configuration format changelog for the format history and latest available version.

    • includes: list [optional]

      A list of configuration files this current file is based on. They are merged in order they are stated. So a latter one could overwrite settings from previous files. The current file can overwrite settings from every included file. An item in this list can have one of two types:

      • item: string

        The path to a kas configuration file, relative to the current file.

      • item: dict

        If files from other repositories should be included, choose this representation.

        • repo: string [required]
          The id of the repository where the file is located. The repo needs to be defined in the repos dictionary as <repo-id>.
        • file: string [required]
          The path to the file relative to the root of the repository.
  • machine: string [optional]

    Contains the value of the MACHINE variable that is written into the local.conf. Can be overwritten by the KAS_MACHINE environment variable and defaults to qemu.

  • distro: string [optional]

    Contains the value of the DISTRO variable that is written into the local.conf. Can be overwritten by the KAS_DISTRO environment variable and defaults to poky.

  • target: string [optional] or list [optional]

    Contains the target or a list of targets to build by bitbake. Can be overwritten by the KAS_TARGET environment variable and defaults to core-image-minimal. Space is used as a delimiter if multiple targets should be specified via the environment variable.

  • env: dict [optional]

    Contains environment variable names with the default values. These variables are made available to bitbake via BB_ENV_EXTRAWHITE and can be overwritten by the variables of the environment in which kas is started.

  • task: string [optional]

    Contains the task to build by bitbake. Can be overwritten by the KAS_TASK environment variable and defaults to build.

  • repos: dict [optional]

    Contains the definitions of all available repos and layers.

    • <repo-id>: dict [optional]

      Contains the definition of a repository and the layers, that should be part of the build. If the value is None, the repository, where the current configuration file is located is defined as <repo-id> and added as a layer to the build.

      • name: string [optional]

        Defines under which name the repository is stored. If its missing the <repo-id> will be used.

      • url: string [optional]

        The url of the repository. If this is missing, no version control operations are performed.

      • type: string [optional]

        The type of version control repository. The default value is git and hg is also supported.

      • refspec: string [optional]

        The refspec that should be used. If url was specified bot no refspec the revision you get depends on the defaults of the version control system used.

      • path: string [optional]

        The path where the repository is stored. If the url and path is missing, the repository where the current configuration file is located is defined. If the url is missing and the path defined, this entry references the directory the path points to. If the url as well as the path is defined, the path is used to overwrite the checkout directory, that defaults to kas_work_dir + In case of a relative path name kas_work_dir is prepended.

      • layers: dict [optional]

        Contains the layers from this repository that should be added to the bblayers.conf. If this is missing or None or and empty dictionary, the path to the repo itself is added as a layer.

        • <layer-path>: enum [optional]
          Adds the layer with <layer-path> that is relative to the repository root directory, to the bblayers.conf if the value of this entry is not in this list: ['disabled', 'excluded', 'n', 'no', '0', 'false']. This way it is possible to overwrite the inclusion of a layer in latter loaded configuration files.
      • patches: dict [optional]

        Contains the patches that should be applied to this repo before it is used.

        • <patches-id>: dict [optional]

          One entry in patches with its specific and unique id. All available patch entries are applied in the order of their sorted <patches-id>.

          • repo: string [required]
            The identifier of the repo where the path of this entry is relative to.
          • path: string [required]
            The path to one patch file or a quilt formatted patchset directory.
  • bblayers_conf_header: dict [optional]

    This contains strings that should be added to the bblayers.conf before any layers are included.

    • <bblayers-conf-id>: string [optional]
      A string that is added to the bblayers.conf. The entry id (<bblayers-conf-id>) should be unique if lines should be added and can be the same from another included file, if this entry should be overwritten. The lines are added to bblayers.conf in the same order as they are included from the different configuration files.
  • local_conf_header: dict [optional]

    This contains strings that should be added to the local.conf.

    • <local-conf-id>: string [optional]
      A string that is added to the local.conf. It operates in the same way as the bblayers_conf_header entry.
  • proxy_config: dict [optional]

    Defines the proxy configuration bitbake should use. Every entry can be overwritten by the respective environment variables.

    • http_proxy: string [optional]
    • https_proxy: string [optional]
    • no_proxy: string [optional]