Ubuntu leaving ZFS users out in the cold again

A simple error message is all that Ubuntu's upgrade tool has zo offer ZFS users

Ubuntu users who use the next-generation file system ZFS cannot upgrade their computers from Ubuntu 24.10 to 25.04 using the official release upgrade tool. A bug report was filed on May 15, 2025, but it appears that it will never be fixed. The reason for the bug, which is classified as a “critical error,” appears to be incompatibilities between ZFS userspace applications and the kernel module, which cause the system to freeze during the upgrade process.

Thanks to ZFS’s snapshot feature, affected users can quickly restore their computers to their previous state by rolling back the file systems in the two ZFS pools installed by Ubuntu. However, this does not solve the upgrade problem, especially since Canonical, the company behind Ubuntu, stopped supporting Ubuntu 24.10 in July 2025. The only thing the Ubuntu developers have done is to patch the release upgrade tool so that the upgrade process is aborted with an error message as soon as a ZFS file system is detected.

For most ZFS users, the only option is therefore to reinstall their computer. However, whether they should stick with Ubuntu and ZFS is a matter of trust. It is not the first time Canonical has left ZFS users out in the cold.

Ubuntu’s mixed history with ZFS

Since 2019 (version 19.10), Ubuntu’s installer supports ZFS on root. OpenZFS is used for this purpose, a free implementation that, for licensing reasons, is not included in the Linux kernel but must be integrated as an external kernel module.

Despite this additional effort, Canonical did not shy away from ZFS at the time and even developed its own system service called zsys, which took care of automatically creating snapshots and integrating rollbacks into the Grub boot manager.

However, Canonical seemed to have overreached itself – not for the first time. Development of zsys stalled in 2022. When the new Ubuntu desktop installer was introduced in 2023, it was unable to set up Ubuntu on ZFS. It was not until Ubuntu 24.04 LTS that ZFS made a comeback in the installer.

The broken upgrade to Ubuntu 25.04 is yet another major glitch. Who would want to rely on the fact that this is the last one?