On Mon, May 16, 2016 at 7:05 PM, Stephen Berg (Contractor)
<[log in to unmask]> wrote:
>
> The logical volume for my home directory is mounted on /export/home locally,
> and /home via NFS/automounter. In the SL5.x and SL6.x days it would have
> been a bind mount and I could filter out bind mounts from the df output,
> everything worked as expected. These days there's no indication that it's a
> bind mount anywhere that I can see, and as you pointed out, it's displaying
> the shorter of the possible mount points to display.
>
> That means that right after a reboot, it shows up mounted on /export/home
> which is correct, but once I login it shows up as /home which isn't correct.
> When running say for instance "df -PTlk" the output shouldn't ever change
> where a filesystem is mounted. But this choosing of the shorter of possible
> mount points means it can change on the fly.
>
> When my monitoring software (OMD/check_mk) does its thing it wants to see
> where the filesystem is mounted during the df part of its check, but when
> it changes arbitrarily it can't adjust for that on the fly.

1) Can your monitoring software be taught that /home and /export/home
are the same?

2) There was a problem with the earlier implementation of "/etc/mtab"
in that you could

mount /dev/sdb1 /path/to/mount
mount -o bind /path/to/mount /path/to/bind-mount
umount /path/to/mount

and still have "/path/to/bind-mount" tagged as "bind" in "/etc/mtab"
because, from the kernel's perspective, running

mount /dev/sdb1 /path/to/mount
mount -o bind /path/to/mount /path/to/bind-mount

is the same as running

mount /dev/sdb1 /path/to/mount
mount /dev/sdb1 /path/to/bind-mount

so "/etc/mtab" was turned into a symlink to "/proc/self/mounts". It's
even become a requirement in systemd but I've forgotten with which
version.

3) An ex-colleague pointed out to me yesterday that one of the reasons
for choosing the shortest path was that otherwise "/rootfs" or
"/newroot" might show up in df rather than "/" if the "first local
mount" had been chosen. He must have been referring to the old
"/dev/root" symlink, but maybe he's right!