df hangs -- nfs related problem

[Patrick O'Callaghan]

On Thu, Jan 8, 2009 at 2:01 PM, Aldo Foot <lunixer at gmail.com> wrote:
> On Wed, Jan 7, 2009 at 7:16 AM, Patrick O'Callaghan
> <pocallaghan at gmail.com> wrote:
>> On Wed, Jan 7, 2009 at 9:33 PM, Rick Stevens <ricks at 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.

Remote X apps don't require NFS per se (though a specific use may).
Also, NFS is usually deprecated for mailstores, as in the past it has
had persistent problems with file locking, being at bottom a stateless
protocol (recent versions may have fixed this, I don't know). Using
maildir is a way round this as it avoids locks.

poc