[HowTo] Install a kernel from Backports

[sunrat]

There are various Backports guides in random places but as the most common reason for Backports is to install a kernel more recent than the one in Stable for hardware support, here's a specific guide.

Add Backports to sources.list:

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deb http://deb.debian.org/debian bookworm-backports main

to /etc/apt/sources.list (or add a new file with the ".list" extension to /etc/apt/sources.list.d/ . I use backports.list)
Update the package database, run:

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apt update

Install kernel metapackages (these will ensure any kernel updates are applied during normal update process):

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apt install -t bookworm-backports linux-image-amd64 linux-headers-amd64

Note: as @fabien posted below, linux-headers is not essential unless you need to build packages. This includes packages which use Dynamic Kernel Module Support (DKMS) such as Nvidia drivers
Reboot to use the new kernel.
That is for the most common amd64 architecture, modify if you use something else but check first if it is available in backports.
That is all!

New(ish) hardware may also require more current firmware. Check if a backports version is available and install it. If not, it is normally safe to install newer firmware packages from Testing or Unstable but do not add those as sources. Rather download the required package and install manually.

More info on Backports - https://backports.debian.org/Instructions/

[fabien]

Thanks @sunrat, just wanted to note that linux-headers-amd64 is not always necessary. It is mainly needed if you use dkms, e.g. to install the nvidia proprietary driver. I guess the rule is, if you already have it installed, install it from Backports, otherwise, don't install it.
How to check if linux-headers-amd64 is installed:

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$> apt policy linux-headers-amd64 
linux-headers-amd64:
  Installed: (none)
  Candidate: 6.1.90-1
  Version table:
     6.7.12-1~bpo12+1 100
        100 https://deb.debian.org/debian bookworm-backports/main amd64 Packages
     6.1.90-1 500
        500 https://deb.debian.org/debian-security bookworm-security/main amd64 Packages
     6.1.76-1 500
        500 https://deb.debian.org/debian bookworm/main amd64 Packages
     6.1.67-1 500
        500 https://deb.debian.org/debian bookworm-updates/main amd64 Packages

In the above case, it is not installed.

Edit 2024-06-05: it is possible that a linux-headers package is installed while the linux-headers-amd64 meta-package is not. Here is a method to display all installed linux-headers packages:

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$> apt list --installed "linux-headers-*amd64"

If this command shows linux-headers packages installed, it is probably advisable to install the linux-headers-amd64 meta-package from Backports.

[sunrat]

Thanks @sunrat, just wanted to note that linux-headers-amd64 is not always necessary. It is mainly needed if you use dkms, e.g. to install the nvidia proprietary driver. I guess the rule is, if you already have it installed, install it from Backports, otherwise, don't install it.

Thanks @fabien . I added a note to my post above. I always install it as I use nvidia drivers and build some other things.

[larienna]

Question, after upgrading the kernel, do I have to remove the backports from the sources.list?

Else, I imagine any further software update will use the backports? Is it necessary since I am using a new kernel, or it's optional only if I want newer software?

[sunrat]

Question, after upgrading the kernel, do I have to remove the backports from the sources.list?

Else, I imagine any further software update will use the backports? Is it necessary since I am using a new kernel, or it's optional only if I want newer software?

Backports inherits a default pin priority of 100 whereas the main repo is 500. This means it won't install or replace anything unless you specifically specify the -t bookworm-backports option when you wish to install a package from backports. I think any packages you do install from backports however will be updated if a new version appears in backports (not 100% sure on this, I'll check later).
I keep backports active in sources, never had any issue.

[fabien]

I think any packages you do install from backports however will be updated if a new version appears in backports (not 100% sure on this, I'll check later).

Yes, because of the ButAutomaticUpgrades: yes field

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$> head -n17 /var/lib/apt/lists/deb.debian.org_debian_dists_bookworm-backports_InRelease
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

Origin: Debian Backports
Label: Debian Backports
Suite: stable-backports
Codename: bookworm-backports
Changelogs: https://metadata.ftp-master.debian.org/changelogs/@CHANGEPATH@_changelog
Date: Tue, 15 Oct 2024 20:21:00 UTC
Valid-Until: Tue, 22 Oct 2024 20:21:00 UTC
NotAutomatic: yes
ButAutomaticUpgrades: yes
Acquire-By-Hash: yes
No-Support-for-Architecture-all: Packages
Architectures: all amd64 arm64 armel armhf i386 mips64el mipsel ppc64el s390x
Components: main contrib non-free-firmware non-free
Description: Debian bookworm - Backports

[larienna]

OK thanks, so I can update in peace

[Danathar]

Once you use a kernel from backports, how does this affect upgrades when going to the next major version (like 13)? I’m contemplating upgrading my hardware soon and will need a later kernel for the newer motherboard, but I wonder what I’ll need to do when upgrade time comes to make sure the upgrade does not break.

Thanks!

[wizard10000]

Once you use a kernel from backports, how does this affect upgrades when going to the next major version (like 13)?

It won't affect an upgrade to 13. Kernels are backported from Testing so there's zero chance a kernel in bookworm-backports will be newer than Trixie's kernel.

Hope this helps -

[Danathar]

Once you use a kernel from backports, how does this affect upgrades when going to the next major version (like 13)?

It won't affect an upgrade to 13. Kernels are backported from Testing so there's zero chance a kernel in bookworm-backports will be newer than Trixie's kernel.

Hope this helps -

Thanks! During my testing, I noticed one thing: using the latest kernel in backports may not be compatible with the kernel modules you are using. When I tried 6.11 with ZFS and NVIDIA, building the modules for both failed. I had to downgrade to 6.9 in backports to get them working. So anybody looking to use a backport kernel needs to be aware of that before they upgrade.

[dynamicsubspace+]

@sunrat, thank you for the backports guide, and @Danathar, thank you for the note about NVIDIA--I installed 6.9 without any issues!

[wizard10000]

@Best_Threads

[DebianFox]

Once you use a kernel from backports, how does this affect upgrades when going to the next major version (like 13)?

It won't affect an upgrade to 13. Kernels are backported from Testing so there's zero chance a kernel in bookworm-backports will be newer than Trixie's kernel.

Hope this helps -

Thanks! During my testing, I noticed one thing: using the latest kernel in backports may not be compatible with the kernel modules you are using. When I tried 6.11 with ZFS and NVIDIA, building the modules for both failed. I had to downgrade to 6.9 in backports to get them working. So anybody looking to use a backport kernel needs to be aware of that before they upgrade.

@wizard10000, @Danathar and @FreewheelinFrank would it be possible to add this information along with other NVidia driver issues to the topic Please read - Current Issues in Debian?

If required I can draft it and then post it.

[FreewheelinFrank]

Thanks! During my testing, I noticed one thing: using the latest kernel in backports may not be compatible with the kernel modules you are using. When I tried 6.11 with ZFS and NVIDIA, building the modules for both failed. I had to downgrade to 6.9 in backports to get them working. So anybody looking to use a backport kernel needs to be aware of that before they upgrade.

@wizard10000, @Danathar and @FreewheelinFrank would it be possible to add this information along with other NVidia driver issues to the topic Please read - Current Issues in Debian?

If required I can draft it and then post it.
[/quote]

Sounds good to me. You can start a topic in Beginners Questions. I have zero knowledge of NVidia, so will have to leave it to other members to validate advice such as that above. If the topic is useful (ie the information is not subject to so many disputations, caveats and conditions that it would be confusing more than helpful), I can certainly add a link to the "Problems" page.