I had a user with this same problem. In his case, he filled up the disk by downloading stuff, then the next time he booted the computer GNOME fails to start, just dumps you back at GDM with no explanation. He had an essay to write and had absolutely no idea why his computer had completely stopped working, or what to do about it. Luckily I was on hand to fix it for him. Teaching him to use the text terminal to correct the problem himself in future is not really feasible, too much knowledge needed.
This is a serious bug, for normal users it amounts to complete system failure if they are neglectful and let their disk get full. Windows XP keeps working when this happens, btw. ** Changed in: gdm (Ubuntu) Status: Unconfirmed => Confirmed -- no indication when login fails due to lack of disk space https://launchpad.net/bugs/35217 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs