I had a pretty vanilla install of 12.04 running on a headless server with a software RAID1 array. I ran do-release-upgrade to upgrade to 14.04, and it seemed to run without issue. The only mistake I think I may have made was that it prompted me to update or keep the grub file, and I told it to update, but I don't think I had anything custom there.
Now, I never get to a prompt. When I boot, I get the Ubuntu-themed grub select screen, but selecting the default option results in a long never-ending scroll of messages that are scrolling too fast for me to makeout. Each line seems to be formatted like:
[ 433.8979798] ata1.00: some message
I can catch some messages like "device error" and "error: (ABRT)", but it's too much of a blur.
If I had to guess, I'd say it's having trouble mounting my md0 RAID partition, but I can't confirm. I've tried selecting different kernels, including recovery mode, but they all result in the same stream of messages.
How do I fix this?
Edit: I found that if I select the server recovery mode kernel, after a few minutes of messages, it does eventually drop a recovery menu which lets me drop out to a root shell, but I'm not sure where to go from there. Nothing seems to work. It says eth0 is up, but all IPs and domains it says are unreachable.
