Importing changes from Debian (merges & syncs)
==============================================

This article explains how and why changes from :term:`Debian` are imported
into Ubuntu.

How does Ubuntu import changes from Debian?
-------------------------------------------

Because Ubuntu is derived from Debian and uses the same package management
system (:term:`APT`), most changes made to Debian can also be applied to
Ubuntu.

**Syncs** and **merges** are the two processes through which Ubuntu developers
integrate updates and improvements from Debian into the
:doc:`/explanation/archive`.

Sync
~~~~

Beginning with the archive opening for a new Ubuntu release until the 
:ref:`DebianImportFreeze`, new :term:`packages <Package>` and packages with
higher version identifiers than the corresponding Ubuntu packages are
automatically copied from Debian unstable (also known as :term:`Code name` 
"Sid") into the Ubuntu package archive if the corresponding Ubuntu packages
do not carry :term:`Ubuntu Delta`. This process is called "synchronisation with
Debian", or "sync" for short.

On request (via a :term:`Launchpad` bug-ticket), 
:term:`Archive Admins <Archive Admin>` can sync a package from Debian even if
the Ubuntu package carries Ubuntu Delta. In this case, the Ubuntu Delta will
be dropped. A good example is when Ubuntu-specific changes have been merged
into the Debian package or :term:`Upstream` project and are no longer needed.

.. note::
    The :ref:`FeatureFreeze` is often scheduled for the same day as the
    :ref:`DebianImportFreeze`.
    
    After the Debian Import Freeze and before the :ref:`FinalRelease`, you
    must also request the respective freeze exception. 

    After the Final Release, you must follow the 
    :doc:`/explanation/stable-release-updates` process. For additional details
    about the freezes, see the :doc:`/explanation/development-process` article.

Merges
~~~~~~

When importing a newer Debian package into Ubuntu, a merge must be performed 
if the corresponding Ubuntu package carries Ubuntu Delta that needs to be
partially or fully applied to the Debian package.

The Ubuntu Merge-o-Matic (MoM) automatically performs merges and publishes the
reports on `this page <https://merges.ubuntu.com/>`_. See the lists of
outstanding merges for:

* `main <https://merges.ubuntu.com/main.html>`_
* `universe <https://merges.ubuntu.com/universe.html>`_
* `restricted <https://merges.ubuntu.com/restricted.html>`_
* `multiverse <https://merges.ubuntu.com/multiverse.html>`_

To complete a merge, interaction and supervision by Ubuntu maintainers are
required. See the :doc:`tutorial </tutorial/merge-a-package>` and
:doc:`how-to </how-to/merge-a-package>` for details on performing a merge.

See the section :ref:`ArchiveComponents` in the article that explains the 
Ubuntu package archive for an explanation of ``main``, ``universe``,
``restricted`` and ``multiverse``.

Why does Ubuntu import changes from Debian?
-------------------------------------------

Ubuntu incorporates changes from Debian through merging and syncing to
leverage the extensive work and improvements made by the Debian community.
Debian provides a stable foundation and a vast repository of packages.
By integrating changes from Debian, Ubuntu can focus on refining the
:term:`user experience`. At the same time, the consistency between Ubuntu and 
Debian allows for sharing resources (e.g., testing and bug fixing) and
contributing back to the open-source ecosystem, ultimately benefiting both
:term:`distributions <distribution>` and their users.