Re: Multiple instances of the same mount point in fstab not possible? (want to layer multiple filesystems into one namespace via union mount option)

[Matthias Petermann <mp%petermann-it.de@localhost>]

Hi Michael,

On 24.09.22 10:42, Michael van Elst wrote:
> mp%petermann-it.de@localhost (Matthias Petermann) writes:
>
> > NAME=data1             /export   ffs     rw,log,union          0 0
> > NAME=data2             /export   ffs     rw,log,union          0 0
> > NAME=data3             /export   ffs     rw,log,union          0 0
>
> > Here, only the first file system is mounted, the other two are ignored.
> > I suspect that multiple occurrences of the same mount point are not
> > supported in fstab.
>
> It's a feature. mount -a skips filesystems that are already mounted,
> so you don't get failures from the attempt to mount a filesystem twice.
> (mount -A forces all mounts).
>
> But your example has another issue, there is no information about the
> order of mounts, so you may end with filesystems stacked incompletely
> or even the wrong order.
>
> The easiest is probably to declare the filesystem 'noauto' and add
> a custom rc script that creates and removes your stacked filesystems.

Thanks - I didn't know the difference between mount -a and mount -A... I 
have skimmed the man page several times but this detail had slipped my 
mind.

With the order of the mounts I assumed that the fstab is processed from 
top to bottom - but that is certainly not quite safe to assume. I was 
afraid that I would have to write my own rc.d script - but the advantage 
would be that I could at least influence that the mounts have to be 
ready before Samba and the NFS server are started.

Many greetings
Matthias

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