Question on mountd

[Ian Lepore]

On Thu, 2017-08-10 at 16:56 +0200, Olavi Kumpulainen wrote:
> Hi guys,
> 
> I notice that mount SIGHUP’s mountd every time mount succeeds. The
> SIGHUP causes mountd to remount all exported directories.If this
> happens while a NFS-client is accessing a share, an access error may
> occur.
> For this purpose, there is an option to mount, -S, which locks nfsd
> while the remount is executing.
> 
> Can anyone of you share why mount needs to SIGHUP mountd in the first
> place? It would make sense if mountd is restarted whenever
> /etc/exports is modified, but always seems like overkill.
> 

Based on looking through the mountd code a bit... When a new filesystem
is mounted, it may be mounted on one of the mount points listed in
/etc/exports.  If there was no fs mounted there previously, then mountd
might have failed to set the in-kernel export attributes the last time
it processed the exports file, so it has to do the processing again
after the mount to update the in-kernel export data.  It would be
really complex for mountd to try to figure out the minimal set of "what
changed" after a mount succeeds, so it just completely reprocesses the
exports file, first removing all export data from the kernel, then re-
applying it all.

So, all in all, I think the right fix for this is to add
"mountd_flags="-r -S" to your rc.conf file (-r is a default from
/etc/defaults/rc.conf).

-- Ian