[TriLUG] can't unmount nfs exported fs

[James Tuttle]

Joseph Mack NA3T wrote:
> 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
> 

I'm no expert, but to unmount a storage array at work I do:

sync
umount -l /mnt/mountpoint

sync, as you may know, flushed buffers and ensures there isn't unwritten
data remaining.  umount -l dismounts a filesystem lazily, not requiring
that every process be finished with a mounted drive.  This is the only
way I've found to dismount our nfs mounted array.

Jim


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---Jim Tuttle
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