How to download Real-time Ubuntu kernel source code
===================================================

The source code for Ubuntu's real-time kernel is available for download.
The following guide will show you how to download it for your system's release of Ubuntu.
The process depends on the release of Ubuntu you are using.

Enable access to the real-time Ubuntu kernel
---------------------------------------------

.. tab-set::
    :sync-group: release

    .. tab-item:: LTS releases (22.04, 24.04, etc.)
        :sync: lts

        .. note::
            LTS releases of Ubuntu require Ubuntu Pro to download their respective real-time kernel source code.
            See the `Ubuntu Pro documentation <https://documentation.ubuntu.com/real-time/en/latest/how-to/enable-real-time-ubuntu/>`_ for more information.

        If you've already enabled the real-time kernel, you don't need to do anything in this step.
        You can verify the ``realtime-kernel`` service is activated with ``sudo pro status``.

        Otherwise, enable access to the real-time kernel source packages with the following command:

        .. code-block:: shell

            sudo pro enable realtime-kernel --access-only


    .. tab-item:: Interim releases (24.10, etc.)
        :sync: interim
        
        The real-time kernel source is freely available in the 
        `universe repository <https://packages.ubuntu.com/oracular/linux-realtime>`_ for interim releases. 
        No actions are required for this step!
    

Enable downloading source packages with apt
--------------------------------------------

APT is used to download the real-time kernel source. We need to enable the source repositories (``deb-src``) to allow ``apt`` to download real-time kernel source packages from its archives.

.. tab-set::
    :sync-group: release

    .. tab-item:: 22.04 LTS
        :sync: lts

        Open the ``/etc/apt/sources.list`` file in a text editor (requires elevated permissions) and :spellexception:`uncomment` (delete the leading ``#``) the line which includes ``deb-src http://archive.ubuntu.com/ubuntu/ jammy main``. 

        .. code-block:: debsources
           :emphasize-lines: 4
           :linenos:

           # See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
           # newer versions of the distribution.
           deb http://archive.ubuntu.com/ubuntu/ jammy main restricted universe multiverse
           deb-src http://archive.ubuntu.com/ubuntu/ jammy main restricted universe multiverse

           deb http://archive.ubuntu.com/ubuntu/ jammy-updates main restricted universe multiverse
           # deb-src http://archive.ubuntu.com/ubuntu/ jammy-updates main restricted universe multiverse

        .. caution::
            Be sure to :spellexception:`uncomment` only the line which includes ``main`` after the release code-name.

    .. tab-item:: 24.04 LTS and newer
        :sync: lts

        Use the following command to add ``deb-src`` to the :file:`ubuntu-realtime-kernel.sources` file:

        .. code-block:: shell
            
            sudo sed -i '2s/^Types: deb$/Types: deb deb-src/' /etc/apt/sources.list.d/ubuntu-realtime-kernel.sources


    .. tab-item:: Interim Releases (24.10, etc.)
        :sync: interim

        Use the following command to add ``deb-src`` to the :file:`ubuntu.sources` file:

        .. code-block:: shell
            
            sudo sed -i '1s/^Types: deb$/Types: deb deb-src/' /etc/apt/sources.list.d/ubuntu.sources

Get the real-time kernel source code
-------------------------------------

First, refresh APT to index newly-added repositories:

.. code-block:: shell 

    sudo apt update

Next, install ``dpkg-dev``, which is required to unpack Debian source packages:

.. code-block:: shell
    
    sudo apt install dpkg-dev

Lastly, download the real-time kernel source code:

.. code-block:: shell

    sudo apt-get source --only-source linux-realtime


.. tip:: 

    Ensure you have enough disk space; the downloaded and extracted packages take almost 2GB of storage.

At this point, the unpacked source files are in your current directory.