[TriLUG] can't unmount nfs exported fs

[Joseph Mack NA3T]

I have an external usb disk which I use as backup. I mount 
it under /backup on the local machine. No problems, can 
rw and umount it (`umount /backup`) when I'm done.

It's useful to use the same external usb disk to backup 
other machines. I then export (nfs) /backup to another 
machine and mount it there (say as 
/name_of_local_machine/backup) and write to it. When I'm 
done I umount it on the remote machine (it's gone, looking 
with `mount` and `df`). Fine so far.

Now I want to `umount /backup` as on the local machine as 
before so I can unplug the usb drive. However now I can't 
umount it on the local machine (device is busy). `lsof | 
grep backup` on the local machine doesn't show anything 
owning it.

My solution so far has been to reboot the local machine. 
This is getting to be a pain.

Is this supposed to happen (surely not)? Do I have a hosed 
system? Any cures, suggestions where to look?

Thanks Joe

-- 
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) wm7d (dot) net - azimuthal equidistant map
generator at http://www.wm7d.net/azproj.shtml
Homepage http://www.austintek.com/ It's GNU/Linux!