Why won't 8.2 umount -f?

Devin Teske devin.teske at fisglobal.com
Mon Feb 13 23:36:34 UTC 2012

> -------- Original Message -------- 
> Subject: Re: Why won't 8.2 umount -f?
> Date: Mon, 13 Feb 2012 13:20:55 -0800
> From: Doug Barton <dougb at FreeBSD.org>
> Organization: http://SupersetSolutions.com/
> To: <freebsd-stable at FreeBSD.org>
> CC: <freebsd-fs at FreeBSD.org>
Cross posting? (gasp!)

> On 02/13/2012 13:02, Doug Barton wrote:
> > Is there some magic I'm missing to convince an 8.2 system to umount -f?
> > I had an NFS server crash, so I'm trying to get the mounts updated. All
> > of the 7.x systems happily did 'umount -f', but the 8.x systems (mostly
> > 8.2-pN) are just hanging forever.
> ... and it gets worse. I just 'shutdown -r now'ed one of my
> less-critical 8.2 systems, and it hung for several minutes after "All
> buffers synced." After a power cycle it came back, but the buffers
> weren't actually synced because it's still fsck'ing some pretty large
> file systems.
> What the heck?

We've noticed this behavior too (on 8.1-RELEASE-p6).

The work-around (to avoid long fsck) is to:

1. Drop to the kernel debugger (Ctrl+Alt+ESC -- requires DDB to be enabled in

2. Type: call boot(0)

This causes the system to attempt a second sync of the buffers. This second
attempt ends up timing out but succeeds in resetting the CPU (after 3x 60s

The price (waiting 180s before cpu_reset() is called) can be well worth it
(avoiding multi-hour fsck) because the disks will be marked clean.

For us, this is a serious issue and like Doug, we too exclaim "what the heck?"
Shouldn't have to drop to kernel debugger and [redundantly] invoke boot(0) after
syncer's hang just prior to cpu_reset().

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