Sometimes, when I reboot, unmounting filesystems tells me that /dev is busy, and then it can't unmount (remount ro) the root filesystem, and asks for the root password for maintenance. What can be the problem? Reproducible: Sometimes Steps to Reproduce: 1.reboot Actual Results: /dev busy can't unmount(remount read-only) root Expected Results: clean reboot
What program has devices in /dev open ? lsof | grep /dev/
sorry, i didn't have time to enter my password - this "emergency maintenace, enter root password or press CTRL+D" prompt hanged for a couple of seconds, then the machine rebooted. will try to check if the problem shows again.
USB keyboard via modules?
no, it's a laptop. i've got a usb mouse, though.
I think I have discovered a reason why this could happen. If the mount_readonly() function in /etc/init.d/halt.sh fails to unmount a filesystem, it is run a second and third time. On the third try, mount_readonly() uses "umount -n -r" and fails with /dev because for some reason it tries to create a /etc/mtab~xxxx lock file (even though the -n option is used) and by that time / has already been remounted readonly. At that stage the whole process fails and dumps you back in the shell. The reason this happened to me is because I have an entry in my /etc/fstab which bind-mounts /proc to some other location (which doesn't always exist). Because mount_readonly() only specifies the mountpoint to mount/unmount, mount tries to remount the wrong /proc (which has a non-existent mountpoint), causing it to fail which then screws up the whole unmounting process. Perhaps this is a bug in umount (it doesn't seem to honour the -n option when -r is used). My problem can be solved, however, by specifying both the filesystem and mountpoint to mount in /etc/init.d/halt.sh's mount_readonly() function. Reproducible: Always Steps to Reproduce: 1. Add the following line to /etc/fstab: /proc /nowhere none bind,noauto 0 0 2. Reboot Actual results: umount: udev busy - remounted read-only can't create lock file /etc/mtab~4628: Read-only file system (use -n flag to override)
what version of util-linux ? umount with 2.12q-r1 seems to only read /etc/mtab although i can confirm that your /proc bind entries does cause issues ...
util-linux-2.12i-r1 baselayout-1.11.13-r1 I will try with util-linux-2.12q-r1.
Created attachment 68338 [details, diff] umount: respect -n when specified with -r Actually, it seems umount does write to /etc/mtab (see mount/umount.c:358), which is exactly the place that causes this failure. With the -n and -r options specified, the logic there seems to be: 1. Try to unmount 2. If it failed, try to remount ro 3. If ro remount succeeded, update mtab The problem is that it tries to update mtab regardless of the -n option. I've attached a simple patch that fixes the problem.
just need to tweak the check with mtab_is_writable() and patch is good to go added to cvs, thanks
