ZFS bpool is almost full; how can I free up space so I can keep updating my system without errors?
Uninstalling old and unused kernels and associated files is the correct action to take; to avoid the suggestion to install an unsigned kernel, remove packages that depend on linux-image-5.11.0-34-generic via:
sudo apt purge linux*5.11.0-34*
The second step required to free up space is to remove old snapshots referencing the files that were removed; list the snapshots via:
zfs list -r -t snapshot -o name,used,referenced,creation bpool/BOOT
You can see in the REFER column how much data is referenced. Identical numbers often coincide with minimal USED values; the snapshots are effectively copies of previous snapshots.
Manually remove the five oldest snapshots via:
zfs list -r -t snapshot -o name,used,referenced,creation bpool/BOOT | head -n 5 | cut -c 35-40 | xargs -n 1 zsysctl state remove --system
Keep removing snapshots until you see space being freed up.
(Source of the last one-liner and more info: https://github.com/ubuntu/zsys/issues/155)
Notes:
-
Growing a ZFS pool is possible if there is unallocated space, but Ubuntu allocates the remaining space to
rpool. Shrinking a ZFS pool in-place is apparently not possible. -
I see auto-snapshotting is turned on for
bpool, but unless you expect any files to change outside of APT, ZSys snapshotting should be sufficient and would reduce the number of snapshots you have to consider. -
To avoid this problem in the future, stay on top of kernel upgrades and remove old ones regularly. Also consider reducing the ZSys garbage cleaning defaults in
/etc/zsys.conf. For an example, see: https://github.com/ubuntu/zsys/issues/155#issuecomment-758902487