package lxd 3.0.3-0ubuntu1~18.04.1 failed to install/upgrade: new lxd package pre-installation script subprocess returned error exit status 1

I have chosen the LXD '4.0' realease path

As the 'do-release-upgrade' will break in the middle on the upgrade process I fix the upgrading myself with this steps:

1) sudo apt purge lxd-client lxd

2) sudo apt update && sudo apt dist-upgrade

afterward lxd runs as expected from snap

rplessl@host:/home/rplessl# ps -ef | grep lxd
root 12596 9709 0 22:22 pts/0 00:00:00 grep --color=auto lxd
root 25885 1 0 22:08 ? 00:00:00 /bin/sh /snap/lxd/14890/commands/daemon.start
root 26047 1 0 22:08 ? 00:00:00 lxcfs /var/snap/lxd/common/var/lib/lxcfs -p /var/snap/lxd/common/lxcfs.pid
root 26059 25885 0 22:08 ? 00:00:01 lxd --logfile /var/snap/lxd/common/lxd/logs/lxd.log --group lxd

I've pushed a fix to the packaging branch with logic to unmount potential mounts before deletion, this should avoid this case, though it's unclear why those were left mounted in the first place.

My fix was after do-release-upgrade and reboot, I just ran "apt --fix-broken install" as instructed by apt, and that seems to have fixed it.

also if it matters, I'm running xen, this is a "guest" OS.

Hello Roman, or anyone else affected,

Accepted lxd into focal-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/lxd/1:0.10 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, what testing has been performed on the package and change the tag from verification-needed-focal to verification-done-focal. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-focal. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

Just tested this update with a running container and the upgrade went through correctly.
It's hard to tell if this would have normally failed given that based on the output, shmounts and devlxd weren't mounted at the time things got purged but it at least shows that the potentially problematic case upgrades properly and that things didn't regress.

This bug was fixed in the package lxd - 1:0.10

---------------
lxd (1:0.10) focal; urgency=medium

  * Disable the "latest" track as it's no longer a valid upgrade target
    when coming from LXD 3.0. (LP: #1964833)
  * Unmount shmounts/devlxd prior to removal. (LP: #1876979)

 -- Stéphane Graber <email address hidden> Mon, 14 Mar 2022 17:45:36 -0400

The verification of the Stable Release Update for lxd has completed successfully and the package is now being released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.