Comment 22 for bug 499773

This is mainly for the benefit of people who search google for this problem and end up here.

I've seen this on several servers. A simple "umount /var/lib/ureadahead/debugfs" removes the errant mtab entry and cleans up df output if it's bothering you.

It's highly unlikely that this mount lying around is causing any actual problems. The only people who have reported disk full problems legitimately had full disks, and the performance degredation just doesn't make sense. It's entirely possible that there is some other coincident problem that is causing the performance problem that the above user reported.

If you are having problems with a full disk issues but df is reporting you have free space, check the output from du. It's possible for a file to be deleted, but held open by a long-running process which prevents that space from being actually freed. This will make df report free space when there actually isn't any. To see if this might be affecting you, run "lsof | grep deleted". If you see any files listed there, especially large ones, see if you can stop the process holding them open and that space will become usable again. It's likely you will see at least a few files in the list, probably log files, temp files, and lock files. Those are likely not worth worrying about.