[linux-lvm] umount returns device is busy

[P. Larry Nelson]

Herbert Poetzl wrote:
> 
> On Mon, Dec 22, 2003 at 04:10:27PM -0600, P. Larry Nelson wrote:
> > I've been using LVM now since sometime this past summer and
> > everything has worked great and as advertised, until I tried
> > to unmount a logical volume.  And this happens on both RedHat
> > 9 and ES_3.
> >
> > I had occasion the other day to unmount one of the mounted raid
> > arrays in order to upgrade some firmware.  When I tried to do an
> > unmount command, I got "device is busy".  Ok, I'm cd'd there
> > from one of my windows or something, so I make sure all open
> > terminal windows are *not* cd'd there.  Redo the umount command
> > with same result.  Weird, something's got a file open. So, I did
> > an lsof command and grep for the device (/dev/VG1/LV1).  Nothing.
> > I try greping for the mount name (/scratch/cdf).  Nothing.
> > It will not let me unmount the logical volume.
> >
> > The system in question is running RedHat 9 w/kernel 2.4.20-24.9smp
> > with RedHat's lvm-1.0.3-12.  I just so happened to have built
> > another system using RedHat's ES_3 w/kernel 2.4.21-4.0.1.ELsmp and
> > their lvm-1.0.3-15, so I thought I'd try it there.  Built an identical
> > logical volume, mounted it, tested it (works fine), tried to umount
> > the filesystem with identical results: device is busy.  Checked
> > again using lsof.  Nothing open on the mounted filesystem.
> >
> > I went checking back thru about 4 months of this list and saw
> > (apparently) that no one else has this problem.  At this point
> > I'm a bit baffled why the umount command isn't working.  I've
> > also seen nothing that might address this in the LVM-HOWTO.
> > Then again, I could have missed it.
> >
> > Ideas?
> 
> maybe some kernel service is holding a reference
> to that device, nfs or samba server comes to mind,
> just try to disable them one after the other and
> see if umount will work ...
> 
> HTH,
> Herbert

That was it.  The nfs daemon had it tied up (we're not running samba).
I tried 'umount -f' and 'umount -l' without success.  Frank Benkstein
suggested using 'fuser -v -m /scratch/cdf' and that returned nothing
as well.  But when I stopped the nfs daemon, it unmounted just fine.

On a hunch, further testing shows that it's not necessary to actually 
stop the nfs daemon, just remove the entry from /etc/exports for the 
filesystem you wish to unmount and run 'exportfs -r'.  That way, apparently,
the nfs daemon no longer cares what you do with the filesystem.  Then, the
umount command works just fine.  But it is interesting that fuser doesn't
indicate that nfsd has a hold on the mounted filesystem.

Thanks to all!
- Larry
-- 
P. Larry Nelson (217-244-9855) | Systems/Network Administrator
461 Loomis Lab                 | U of I, CITES Departmental Services
1110 W. Green St., Urbana, IL  | Consultant to: High Energy Physics Group
MailTo:lnelson at uiuc.edu        | http://www.uiuc.edu/ph/www/lnelson
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