Comment 98 for bug 1073433

It turned out to a kind of mystery. No files are left open for writing
but device is busy and can not be cleanly remounted readonly.
Moreover it is not clear how to reproduce the issue.

Concerning the formalities, since the issue addressed
in the last comments have nothing with bug lp: #1124803
"NetworkManager doesn't respond to SIGTERM in daemon mode",
the link to that bug might be removed. On the other hand
original description of this bug fitted quite well
to bug lp: #1124803 and it has nothing
common with removing of network-manager, plymouth, etc.
In my opinion the case with no bunch of packages should be filed
as a dedicated bug with clear statements concerning conditions
and ruled out hypotheses.

Alexander, actually I can not figure out which way debug scripts
can block umount, but since they provide no useful info,
it is interesting what would happen if you completely remove
debug scripts and temporally set
HALT=halt
in /etc/default/halt to have time to inspect last messages
without writing them to a file.

Have you tried memtest on that box? Have you experienced
kernel panic or Oops due to kernel modules or hangs
due to e.g. graphics card driver?

Concerning the bug lp: #1124803, there are tails of
modem-manager and so network-manager again.
I can not comment on plymouth hangs since removing
of "quiet" and "splash" from GRUB_CMDLINE_LINUX_DEFAULT
works like a charm for me. (Actually I have tried
an upstart task with "/bin/plymouth hide-splash"
command before.)

To obtain more debug info I would suggest to run

sudo initctl log-priority info

before shutdown
(perhaps 'sudo sysctl kernel.printk="7 4 1 7"'
to see the messages on the screen as well)
and add

dmesg > /upstart-messages.log

to /etc/init.d/umountroot

There is an issue with network manager proliferated to
plenty of bugs, but it can be easily fixed. The problem
with busy / when no processes are left and
no files are open is very strange.