I was using the OpenmediaVault login and suddenly it had stopped working telling me my username and password were wrong.
I had set everything up, and I've been transferring files to the drive but it wouldn't let me in.
I SSH'd in and noticed a full /var/log with nothing visibly in it.
I fired up a lsof |grep /var/log and there were a list of files marked as deleted that something had deleted but not disconnected the inodes, so a quick /etc/init.d/rsyslog restart cured the issue.
So if anyone cannot log into the web gui in the future, check the /var/log and if its 100%, restart rsyslog and see if that fixes the problem.
Once the rsyslog had restarted, login was fine.