Your first kernel package¶

This tutorial guides you through packaging your own custom Linux kernel using ukpack.

Requirements¶

You need a Git repository containing your custom kernel tree. For this tutorial, we use the upstream Linux kernel and modify it to simulate a custom kernel.

Install dependencies¶

Ensure the required packages are installed:

sudo apt-get update
sudo apt-get install git wget devscripts

Clone required repositories¶

Clone the ukpack repository:

git clone https://kernel.ubuntu.com/forgejo/esmil/ukpack.git

Create a custom kernel repository¶

Now create a new repository for a custom kernel based on the official upstream Linux kernel, 6.6.20.

git clone --depth 1 --branch v6.6.20 \
  https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git \
  custom-linux
cd custom-linux/

Make an example change to the kernel¶

To simulate a custom kernel for this tutorial, modify the EXTRAVERSION field in the Makefile. Here is where you apply your changes.

sed -i 's/^EXTRAVERSION =$/EXTRAVERSION = -custom1/' Makefile

Now, commit the change:

git add Makefile
git commit -m "Add custom EXTRAVERSION"

Sync with upstream kernel¶

Get the upstream Linux kernel tag corresponding to the version the custom kernel is based on:

git remote add linux-stable \
  https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
git fetch --no-tags linux-stable tag v6.6.20

This tag is used to produce a diff between the custom kernel tree and the upstream one. That the tag is correctly fetched can be checked with git tag | grep v6.6.20.

Define the kernel package configuration¶

Inside the custom-linux directory, create a custom_kernel.toml file:

linux-tutorial (6.6.20-1.1ubuntu1) noble; urgency=medium

 * Initial packaging

 -- Your Name <[email protected]> Wed, 12 Mar 2025 14:02:38 +0100
---
arch = "riscv64"
# Use the architecture's upstream defconfig
config = "defconfig"
orig = "v6.6.20"

[pkg.source]
Maintainer = "[email protected]"

The name of the kernel package should always be of the form linux-<custom flavour>, and the version should be of the form <kernel_version>-<local_version>, where <kernel_version> is the Linux kernel source on which the custom kernel is currently based. Also, this tutorial uses the noble Ubuntu release.

Build the kernel package¶

Download the Linux kernel source on which the custom kernel is currently based, which in this case is Linux version 6.6.20, create an output directory outside your kernel tree, and run ukpack:

wget -P .. https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.6.20.tar.xz
mkdir ../ukpack.output/
../ukpack/ukpack -o ../linux-6.6.20.tar.xz \
  -d ../ukpack.output/ custom_kernel.toml

Sign the package¶

Move to the output directory and sign the package:

cd ../ukpack.output
debsign *.changes

Next steps¶

After signing, you can install or upload the package for further testing.