Something bad happened the other day when one of the Ubuntu machines at home was part way through a distribution upgrade; it unexpectedly shutdown. That might have been caused by overheating (intensive work while sitting on a sunny tabletop) but the result was that it only booted to a command prompt. I was considering a reinstall but then I remembered that this was Linux so I went surfing for clues instead.
A key set were found on the AskUbuntu forums. Since I could log in, I could run:
dpkg --configure -a
To reconfigure packaging information. The next three commands did some work but were limited because the network was not running (and not available):
apt-get -f install apt-get -m install apt-get dist-upgrade
That didn’t matter though – I tried a restart and it came back to a working GUI, with networking, from where I was able to open up another command prompt and finish off the rescue. Huzzah for the Advanced Package Manger (APT) and the commandline interface (CLI)!