I accidentally pressed Ctrl+C during Ubuntu Server's
do-release-upgrade process. I'd dropped to a shell to compare a .conf file in /etc/. When I pressed Ctrl-C, it asked whether I wanted to try to reattach to the upgrade process, but it failed to do so.
So I quit, and now there's a hanging dpkg process which is holding onto the apt lock. This is a virtualised server with no GUI frontend...
Is it possible to recover the upgrade process, or do I have to kill the dpkg process and start again?
AFAICT, there was no way to reattach to the upgrade process. However, it wasn't a disaster at all. I killed the hanging dpkg process, and then ran
dpkg --configure -a. This walks you through reconfiguring all packages already installed on the system, tidying up any problems whilst it does so. After that, I used
aptitude to upgrade the remaining packages, which had already been downloaded, but hadn't been installed or configured.