Comment 7 for bug 998512

After upgrading from 11.10 to 12.04 Precise, I too suffered from the unclean-shutdown->disk-check-on-every-startup problem. I found the cause of my problem last week thanks to info from the various posts below. I am reporting it here in case it is relevant.

At first, I guessed that Network Manager was to blame, especially since I am also having problems with a hang at shutdown which I suspect is to do with unmounting some CIFS shares. NM however was not the cause but in following the advice in this bug report
https://bugs.launchpad.net/ubuntu/+source/network-manager/+bug/963106
I added some diagnostic logging to the /etc/init.d/umountroot script as described in message #5.

This showed that plymouthd was still running at the time it should have terminated and this led me to this posting
http://ubuntuforums.org/showthread.php?t=2008576
which in turn led me to
https://bugs.launchpad.net/ubuntu/+source/upstart/+bug/1019347

I followed the suggestion in comment #7 of bug 1019347 and added the line
/bin/plymouth quit
to the /etc/init.d/umountroot script just before root is remounted read-only. (This is the same point that the diagnostic logging described in 963106 had been inserted.)

Result: clean shutdowns and no more disk checks on each and every start.

Now, it must be said that there are other candidates for the cause of this problem and it is worth looking at these too if you find that plymouthd is behaving itself on your system. One that was relevant to me is ensuring you use the latest Nvidia driver if you use proprietary Nvidia graphics in your system. Google for
12.04 nvidia shutdown
to find lots of reports. I upgraded to the latest Nvidia driver but the unclean shutdown continued until I fixed the plymouthd problem.