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Re: df hangs -- nfs related problem



On Wed, Jan 7, 2009 at 7:16 AM, Patrick O'Callaghan
<pocallaghan gmail com> wrote:
> On Wed, Jan 7, 2009 at 9:33 PM, Rick Stevens <ricks nerd com> wrote:
>>
>> Try "lsof | grep nfs" to see if anything has the mountpoint open.  If
>> not, try "umount -f /mnt/nfs" as the root user to try a forced umount.
>>
>> Also check to see if the mount command (or /etc/fstab entry) has "hard"
>> specified (that's the default as well).  Unless you're really certain
>> about the stability of the network and of the NFS server, I'd recommend
>> you specify "soft" in the mount command (see "man 5 nfs" for details).
>
> That would depend on which is worse, potentially losing data or having
> a client machine hang because the server is (perhaps temporarily)
> unavailable. It depends totally on the specific application scenario.
> To quote nfs(5):
>
> <quote>
> A  so-called  "soft"  timeout can cause silent data corruption in
> certain cases. As such, use the soft option only when client
> responsiveness is more important than data integrity.  Using NFS over
> TCP or increasing the value of the retrans option  may  mitigate some
> of the risks of using the soft option.
> </quote>
>
> IOW there is no "right" answer to this.
>
> poc

The command "umount -f" fixed my problem. Thanks Rick.
I had tried "umount -k", which works in older RedHat8
boxes; clearly I've got to re-read the man pages now and then.

So, it appears a soft mount may be ok for read-only operations but not
ideal for things such as remote X-applicatons or filesystems
such as /home or /var/mail. It's wise to make the distinction between hard
and soft mount --great pointer.

~af


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