Unwedging Ubuntu

Upgraded my Linux desktop to Ubuntu 11.04. Kicked it off before I went to bed. Woke up sometime in the middle of the night and wandered down to check on it. It had gotten wedged at some point. The only thing to do was reboot.

It came back up unable to mount the / partition (the only non-swap partition). It dropped me to a command prompt with / mounted read-only. e2fsck reported everything ok. So, what up?

Spent a while last night poking at it and Googling around, to no avail. Got a sysadmin buddy of mine to drop by. He was also largely mystified. Eventually, we stumbled across this post, which sounded pretty close to my symptoms. Tried it; it worked.

So, for posterity, reference, and backup, here's the fix:

mount -o remount,rw /
dpkg --configure -a
sync
reboot

The instructions also say to remount the drive read-only, but that failed on "drive busy", and didn't seem to make a difference.