Introduction

By default, Ubuntu systems run with the Ubuntu kernels provided by the Ubuntu repositories. However it is handy to be able to test with unmodified upstream kernels to help locate problems in Ubuntu kernel patches, or to confirm that upstream has fixed a specific issue. To this end we now offer select upstream kernel builds. These kernels are made from unmodified kernel source but using the Ubuntu kernel configuration files. These are then packaged as Ubuntu .deb files for simple installation, saving you the time of compiling kernels, and debugging build issues.

These kernels are not supported and are not appropriate for production use. Additionally, these kernels do not receive any security updates, therefore if you install them manually via the Mainline PPA, you will never receive a security update or patch for that version.

How do I install an upstream kernel?

Following these steps in order will help you successfully test an upstream kernel.

Prepare OS to install an upstream kernel

First, if one is using select proprietary or out-of-tree modules (e.g. bcmwl, fglrx, NVIDIA proprietary graphics drivers, VirtualBox, etc.) unless there is an extra package available for the version you are testing, you will need to uninstall the module first, in order to test the mainline kernel. If you do not uninstall these modules first, then the upstream kernel may fail to install, or boot.

Choose the proper upstream kernel files

The build directories are nicely organized into per architecture groups. For example, if one is using a 64-bit/amd64 architecture and wants the generic kernel version you would want those files marked A, from the appropriate group.
If you want the low latency version, B.

  Build for amd64 succeeded (see BUILD.LOG.amd64):
AB  linux-headers-4.19.0-041900_4.19.0-041900.201810221809_all.deb
A   linux-headers-4.19.0-041900-generic_4.19.0-041900.201810221809_amd64.deb
B   linux-headers-4.19.0-041900-lowlatency_4.19.0-041900.201810221809_amd64.deb
A   linux-image-unsigned-4.19.0-041900-generic_4.19.0-041900.201810221809_amd64.deb
B   linux-image-unsigned-4.19.0-041900-lowlatency_4.19.0-041900.201810221809_amd64.deb
A   linux-modules-4.19.0-041900-generic_4.19.0-041900.201810221809_amd64.deb
B   linux-modules-4.19.0-041900-lowlatency_4.19.0-041900.201810221809_amd64.deb

Download upstream kernel files from the Ubuntu archive

• Available From: Ubuntu Mainline Kernel Archive (sorted by most recent build)

The Mainline kernel archive has a directory for each tagged release version, with packages for the generic and lowlatency configurations inside.

Install all upstream kernel files

Execute the following command against each of the downloaded files in a terminal of your choosing:

sudo dpkg -i FILENAME.deb

If no errors show up, reboot while holding Shift then select "Advanced options for Ubuntu", then select and boot into the new entry that looks something like:

*Ubuntu with Linux 5.5.13-050513-generic

Problems installing upstream kernels

Virtualbox

Some errors that may occur while attempting to install an upstream kernel are the result of VirtualBox being installed. For example,

'''Error!'''

Bad return status for module build on kernel: 3.7.0-030700rc2-generic (x86_64)
Consult /var/lib/dkms/virtualbox/4.1.18/build/make.log for more information.

As per above, you need to either install the modules-extra package, if available, or uninstall VirtualBox.

Unsatisfied dependencies

A failure to install can also result from the installed version of Ubuntu lacking the newer packages the upstream kernel is dependent on for the install to succeed. For example,

...depends on libssl1.1 (>= 1.1.0); however: Package libssl1.1 is not installed.

If you already have the package referenced by the error message (in this instance, libssl1.1) installed but the version number is beneath the new kernel's requirements, then you would first need to upgrade your Ubuntu installation to a newer release. However, if libssl1.1 is not installed at all, and the version that comes with your release is sufficient, then install libssl1.1.

Other install errors

If for some reason the kernel you attempted to build failed, and it's not due to the above, then continue to test the next most recent kernel version until you can test to the issue.

Uninstalling upstream kernels

The upstream kernels have their own ABI namespace, so they install side by side with the stock Ubuntu kernels (each kernel has a separate directory under /lib/modules/VERSION for example). This means that you can keep several mainline and Ubuntu stock kernels installed at the same time and select the one you need from the GRUB boot menu.

If you want to uninstall an upstream kernel once your need for installing it has abated, execute the following to find the exact name of the kernel packages you need to uninstall:

dpkg -l | grep "linux\-[a-z]*\-"

and then execute the following to uninstall them:

sudo apt purge ''<KERNEL_PACKAGES_TO_REMOVE>''

Remember that several packages can belong to one kernel version; common headers plus the architecture specific headers, image and modules are to be expected at a minimum.

Mainline kernel build toolchain

These kernels are built with the toolchain (gcc, g++, etc.) from either the most recent Ubuntu stable release or development release, at the discretion of the Kernel Team. (21.10 "Impish Indri" and 22.04 "J. J." respectively, as of October 2021) Therefore, out-of-tree kernel modules you already have built and installed for use with your release kernels on LTS releases are not likely to work with the mainline builds (unless the LTS release is also the most recent release, a/k/a from Late April to Late October in even-numbered years).

Mainline kernel mapping to Ubuntu kernel

• See Also: Ubuntu kernel version mappings

The Ubuntu kernel is not bit-for-bit the same as the mainline. However, one may find the upstream release that the Ubuntu kernel is based on via the Ubuntu to mainline mapping table.

Support (BEWARE: there is none)

The mainline kernel builds are produced for debugging purposes and therefore come with no support. Use them at your own risk.

Kernel source code trees

In each directory of the above-linked archive there is a file named <kbd>COMMIT</kbd> which defines the base commit in Linus Torvalds' master tree from which they were built. The patches in the same directory ????-* are applied on top of this commit to make the build tree. A mirror of Linus' tree is available from git://git.launchpad.net/~ubuntu-kernel-test/ubuntu/+source/linux/+git/linus--linux.

First download the COMMIT and patch files ????-* from the mainline build in question to a temporary directory:

git clone git://git.launchpad.net/~ubuntu-kernel-test/ubuntu/+source/linux/+git/linus--linux mainline && cd mainline
git checkout -b $(cat ${MAINLINE}/COMMIT)
git am ${MAINLINE}/????-*

Verifying mainline build binaries

To provide verification that the published builds are 1. built by the Ubuntu mainline build system, and 1. are bit-for-bit identical copies of the files on the server,

the individual files are checksummed and the results are published as a file named <kbd>CHECKSUMS</kbd> in the same directory. This file is in turn signed by the mainline builder using the GPG key below, which can be validated against its record from the Ubuntu Keyserver.

pub   2048R/17C622B0 2008-05-01
      Key fingerprint = 60AA 7B6F 3043 4AE6 8E56  9963 E50C 6A09 17C6 22B0
uid                  Kernel PPA <kernel-ppa@canonical.com>

The verification can be done by running the following commands:

1. Import the above public key to your keyring (if you haven't already done that):

     $ gpg --keyserver hkps://pgp.mit.edu --recv-key "60AA7B6F30434AE68E569963E50C6A0917C622B0"

2. Download the CHECKSUMS and CHECKSUMS.gpg files from the build directory and verify if the CHECKSUMS is signed with the above key:

     $ gpg --verify CHECKSUMS.gpg CHECKSUMS
   
           gpg: Signature made .... using RSA key ID 17C622B0
           gpg: Good signature from "Kernel PPA <kernel-ppa@canonical.com>"
           gpg: WARNING: This key is not certified with a trusted signature!
           gpg:          There is no indication that the signature belongs to the owner.

3. Verify the checksums of downloaded deb files:

     $ shasum -c CHECKSUMS 2>&1 | grep 'OK$'

   You should get a line ending with "OK" for each of downloaded deb file and each type of checksums that are given in the CHECKSUMS file.

Upstream kernel details

We currently build five sets of upstream kernels. All formal tags from Linus' tree and from the stable trees, plus:

1. the daily tip of Linus' linux kernel source tree,

2. the tip of the drm-next head of Dave Airlie's linux repository daily,

3. the tip of the drm-intel-next head of Keith Packard's linux repository daily until 2012, after which it has been taken over by Daniel Vetter at http://cgit.freedesktop.org/drm-intel/, and in particular, the drm-intel-next branch,

4. the tip of the master branch of the debloat-testing tree daily,

5. tags from the combined v2.6.32.x.y tree (by StefanBader) which is v2.6.32.x with DRM from 2.6.33.y.

This makes these kernels closer to the Lucid kernels which are based on 2.6.32 kernels with DRM backported from the 2.6.33 series.

The tagged releases (as made by Linus and the stable maintainers) are found under a directory matching their tag name and which kernel configuration they were built with (<tag>-<series>).

Daily tip of the tree builds are found in the daily sub-directory named for the date they were made.

Each build directory contains the header and image .deb files for the generic flavour i386 and amd64 architectures, as well lowlatency.

Can I install and use a mainline kernel in a live environment?

No. One has two choices to use a mainline kernel:

1. Install the mainline kernel in an installed environment, restart, and choose this newly installed kernel.
2. Build a live environment with the new kernel in it. Given the amount of effort involved in doing this, it is easiest to use an installed OS to test the mainline kernel.