How to delete ZFS snapshots in bulk and upgrading to non LTS version?

Solution 1:

You can list ZFS snapshots in the terminal with the following command:

zfs list -t snapshot

To remove a specific snapshot, you can do this:

sudo zfs destroy rpool/USERDATA/MHT@FRIDAY09-03-21

If you would like to remove all snapshots — damn the torpedoes! — you can do this:

sudo zfs list -H -o name -t snapshot | xargs -n1 zfs destroy

Be careful when issuing zfs destroy commands, because there is no undo.

As for your second question, the window to upgrade from 20.04 ⇢ 20.10 ⇢ 21.04 has closed, as 20.10 is no longer supported. The simplest way to get your machine up to 21.04 would be to reinstall the OS using the newer installation .iso.