.. SPDX-License-Identifier: CC-BY-SA-2.0-UK

Creating Your Own Distribution
******************************

When you build an image using the Yocto Project and follow the default setup
showcased in :doc:`/dev-manual/start`, you are using the :term:`Poky` reference
distribution.

Poky is explicitly a *reference* distribution for testing and
development purposes. It enables most hardware and software features
so that they can be tested, but this also means that from a security
point of view the attack surface is very large. Additionally, at some
point it is likely that you will want to gain more control over package
alternative selections, compile-time options, and other low-level
configurations. For both of these reasons, if you are using the Yocto
Project for production use then you are strongly encouraged to 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
   ":ref:`dev-manual/layers:Creating Your Own Layer`"
   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``).

   .. note::

      The :term:`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:

   - :term:`DISTRO_NAME`

   - :term:`DISTRO_VERSION`

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

   - :term:`DISTRO_FEATURES`

   - :term:`DISTRO_EXTRA_RDEPENDS`

   - :term:`DISTRO_EXTRA_RRECOMMENDS`

   - :term:`TCLIBC`

   .. tip::

      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 another distribution such as Poky as a reference.

-  *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 :term:`Build Directory`, set your :term:`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
      ":ref:`dev-manual/layers:creating your own layer`" and
      ":ref:`dev-manual/layers:following best practices when creating layers`"
      sections.

   -  Add any image recipes that are specific to your distribution.

   -  Add a ``psplash`` append file for a branded splash screen, using
      the :term:`SPLASH_IMAGES` variable.

   -  Add any other append files to make custom changes that are
      specific to individual recipes.

   For information on append files, see the
   ":ref:`dev-manual/layers:appending other layers metadata with your layer`"
   section.

Copying and modifying the Poky distribution
===========================================

Instead of creating a custom distribution from scratch as per above, you may
wish to start your custom distribution configuration by copying the Poky
distribution provided within the ``meta-poky`` layer and then modifying it.
This is fine, however if you do this you should keep the following in mind:

-  Every reference to Poky needs to be updated in your copy so that it
   will still apply. This includes override usage within files (e.g. ``:poky``)
   and in directory names. This is a good opportunity to evaluate each one of
   these customizations to see if they are needed for your use case.

-  Unless you also intend to use them, the ``poky-tiny``, ``poky-altcfg`` and
   ``poky-bleeding`` variants and any references to them can be removed.

-  More generally, the Poky distribution configuration enables a lot more
   than you likely need for your production use case. You should evaluate *every*
   configuration choice made in your copy to determine if it is needed.
