Fix ZFS Linux Kernel Dependency on Arch Linux

Update 2025-12-20: add section about using local repo.

Problem

When updating an Arch Linux system, if you have some third-party repos added, the packages in them sometimes depend on an older package that’s not available in the official repos anymore. In such cases, pacman cannot upgrade the system unless you exclude the impacted package.

ZFS is an example of this. Since Arch Linux doesn’t ship ZFS packages in official repos, I added a third-party one archzfs. However, ZFS support doesn’t always catch up with the newest kernel. When this happens, the upgrade will break.

There is another repo that’s supposed to host the matching kernel version. It can be added by the following section in /etc/pacman.conf:

[zfs-linux]
Server = http://kernels.archzfs.com/$repo/

However, it also often lags behind. See this Github issue for the most recent example.

Manual Force Downgrade Packages

Arch Linux has archives for old packages. There are command line tools like downgrade to install the packages from archives instead of from the repo. So we can install the desired version of dependencies with downgrade.

When installing a specific version with downgrade, if it breaks other packages, it will refuse to continue installing. You can resolve it by installing multiple packages at once in the dependency chain, for example:

sudo downgrade linux linux-headers

It will ask you version for each package.

However, it will fail to install since it will break the dependency of the current installed zfs-linux package. Even if you add zfs-linux to the downgrade list, it doesn’t check for the version that will be installed.

One way to resolve it is by removing zfs-linux first, then run the command above to install desired version of linux packages, then install the newer of version of zfs-linux back.

When you run pacman -Syu again, you will still get an error like this:

error: failed to prepare transaction (could not satisfy dependencies)
:: installing linux (6.18.1.arch1-2) breaks dependency 'linux=6.17.9.arch1-1' required by zfs-linux

But it’s safe to ignore the kernel related packages now by using the --ignore flag:

sudo pacman -Syu --ignore linux --ignore linux-headers

Important: you may have noticed that we include the package linux-headers in the commands above, even though pacman doesn’t complain if we don’t do that. That’s because in Arch Linux, linux-headers doesn’t depend on a specific version of linux. However, if you have a version mismatch, it may break some dkms modules. So it’s better to always keep them in sync.

Use Local Pacman Repo

The approach described above can resolve the dependency conflicts, however, it always feels very risky to manually remove an important package like zfs-linux even it’s just temporarily. If we want to rely on pacman to resolve the dependencies without error, we can use local pacman repo. Here is how to do that:

First, still run the downgrade command above to select desired version of packages:

sudo downgrade linux linux-headers

It will download the packages to /var/cache/pacman/pkg even if it will not install the packages because of failed dependency check.

Then we can copy the downloaded packages to another folder that will be used as a local pacman repo:

sudo mkdir /var/pacman-local-repo
sudo cp /var/cache/pacman/pkg/<packages> /var/pacman-local-repo

Then make it a valid repo:

cd /var/pacman-local-repo
sudo repo-add local-repo.db.tar.gz *.pkg.tar.zst

At last add the local repo to /etc/pacman.conf:

[local-repo]
SigLevel = Optional TrustAll
Server = file:///var/pacman-local-repo

Then just run pacman -Syu and it will find the matching dependency versions in local-repo.

Remember to comment out the section after the upgrade is done, since you don’t want the old packages always in the config.