Comment 0 for bug 1876506

When upgrading from 19.10 (w/ LVM + encypted disks) to 20.04, the installer hangs when trying to probe an LVM snapshot volume created before the upgrade.

Steps to reproduce:

lvcreate -s -L 20G -n preupgrade /dev/vgubuntu/root
do-release-upgrade -d

The installer will hang after the following message:

/usr/sbin/grub-probe: error: unknown filesystem.
Found Ubuntu 19.10 (19.10) on /dev/mapper/vgubuntu-preupgrade
done

Resolution:

Killing the grub-mount process which is probing the LVM snapshot seems to unhang the installer and allow the upgrade to complete without issue.