Re: OK to mount multiple FS in one dir?

[Peter Samuelson <peter@cadcamlab.org>]

[Michael D. Crawford]
> I found I could mount three partitions on /mnt

Yes.  New feature, appeared in the 2.4.0test series, or shortly before.

> and they'd all show up as mounted at /mnt in the "mount" command, but
> if I unmounted one of them (only tried with the currently visible
> one), then it appeared that there were no filesystems mounted there,
> but I could continue umounting until the other two were gone.

util-linux gets rather confused by this feature.  They say newer
versions fix this.

> But I had the 2.10r util-linux sources on my machine and installed
> mount and umount from it, and I find that it gets it right mostly
> when I mount and unmount multiple things, with the exception that if
> /dev/sda5 was mounted before /dev/sda1, then if I give the command
> "umount /dev/sda5", sda1 is the one that gets unmounted rather than
> sda5, so it takes the most recently mounted filesystem rather than
> the one you specify.

I think this is a kernel limitation.  'umount' takes '/dev/sda5' and
turns it into '/mnt/test' and calls umount("/mnt/test").  The kernel
then unmounts whatever is on "top" of /mnt/test.

I don't think there's anything umount can do about this behavior.

Peter
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