Recover from a disconnected remote `do-release-upgrade` session

New Ubuntu Release

You log in over ssh and see this MOTD banner; woohoo new release!

481 updates can be applied immediately.
To see these additional updates run: apt list --upgradable

New release '22.04 LTS' available.
Run 'do-release-upgrade' to upgrade to it.

So you do-release-upgrade - it starts, spawns a new screen session, you accept the scary warnings, and you're off.

Then, the client machine from which you were doing the update crashes (BSOD, kernel panic, what have you) and your session is lost.

Easy Recovery

Since do-release-upgrade spawned a screen session, you can simply reattach to it.

When you log in to your server and you will likely find a pts session open for root. This is the upgrader.

ubuntu@pi:~$ who
ubuntu   pts/0        2022-05-16 22:36 (192.168.0.x)
root     pts/1        2022-05-16 22:38 (192.168.0.x:S.0)

Switching to root, you see there is an attached screen session:

ubuntu@pi:~$ sudo su
root@pi:/home/ubuntu# screen -ls
There is a screen on:
        3915.ubuntu-release-upgrade-screen-window       (05/16/22 22:38:22)     (Attached)

Simply screen -d -r and you can take over the screen session and continue the update / follow its progress.