If you happen to have tried upgrading Ubuntu 24.10 (probably – I didn’t check before getting this done) to Ubuntu 25.04 with ZFS, you will realise that the upgrade is blocked because of known issues. Specifically (without having seen the issue personally), the upgrade blocks at a certain point where the userland ZFS tools have been upgraded and the old kernel is still running.
Fair enough, but why hasn’t it been fixed? Or even a suggested work-around?
One suggestion I came across was to remove the ZFS storage pool(s), upgrade, and add them back in. For those not familiar with ZFS, this is done by simply importing the previously exported (or not) pool without loss of data.
Although backups are as always a good idea!
But there’s more to the suggestion than that, so here are my working notes … the ones written down long-hand with a pen on paper (something I rarely do these days) :-
- Shut down the virtual machines.
- Shut down the gooey – as in shut down the applications, and return to the login screen.
- Switch to a text console (most of the work is done here).
- Shut down the containers.
- Unmoun the ZFS filesystems
- zfs unmount -a
- Which failed, so killed off various running processes with pkill -u ${USER}
- A second zfs unmount -a also failed and had to kill off various other processes until it worked.
- Export the pool which failed – including a second attempt when forced.
- Removed the ZFS packages :-
- dpkg –remove zfs-zed zfs-utils-linux zfs-dkms
- Rebooted as Linux still thinks ZFS is enabled.
- Upgrade started in text mode.
- Skips past the ZFS block and completes normally.
- Added the ZFS pages back (zfs-zed zfs-utils-linux zfs-dkms) and imported the pool. This did issue a dire warning about potential data loss with ZFS and this version of the Linux kernel. With any luck this is an outdated warning and perhaps more to do with ZFS root.
But that dire warning is probably worth avoiding the upgrade.
