umount: device is busy

[Bill McGonigle]

Strange umount problem today:

   #umount -v /mnt/backup/
   umount: /mnt/backup: device is busy
   umount: /mnt/backup: device is busy

Normally this means something is using a file, or someone has a shell 
open in one of the device's directories.  So, ordinarily, I can use 
lsof and/or look for running open shells, take care of the offending 
processes, and do the umount.

This one is strange, however.  I stopped all running processes, save 
syslog, getty, and my login shell/sshd and still can't unmount the 
drive.  No swapfiles on the drive.

Rebooted the system (I know, cheating) and see the same thing.

Practically, I solved this by commenting out the /etc/fstab entry, but 
academically I'm curious what else might have a grip on the device.  It 
_seems_ like it must be the kernel, but why I'm not sure or where to 
look.

The double-reporting of 'device is busy' must be a clue, but I'm not 
sure what it means.

Any ideas?

-Bill
-----
Bill McGonigle, Owner           Work: 603.448.4440
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