Peeking at the contents of a mount point

[Karl Auer]

On Wed, 2012-09-12 at 07:53 -0700, Kevin O'Gorman wrote:
> > You can see the contents of the mountpoint under a mounted filesystem by
> > binding the mount point to another name:
> >
> >    mount --bind /mnt /mnt_view
> >
> > ... then "ls /mnt_view" should show you the "hidden" files.
> >
> > This is from memory, so do please test carefully.
> >
> > Regards, K.
> 
> 
> That's what I thought too, but it does not work.  The --bind option
> lets me place part of the heirarchy in multiple places, but does not
> allow me to expose any underlying mount points.

You forced me to go check. As I stated it, I was indeed wrong. I should
have expressed myself more carefully. If you use --bind to "alias" a
directory, then the contents of that directory remain available under
the alias, even if the directory is later used as the mountpoint for
another filesystem.

That is, you can "protect" the contents of a directory so that they
remain accessible, but you have to do it before the directory is used as
a mountpoint:

kauer at karl:~$ ls /mnt
kauer at karl:~$ mkdir fred
kauer at karl:~$ touch fred/blah
kauer at karl:~$ ls fred
blah
kauer at karl:~$ sudo mount --bind /home/kauer/fred /mnt
kauer at karl:~$ ls /mnt
blah
kauer at karl:~$ sudo mount -o loop ubuntu.iso /home/kauer/fred
mount: warning: /home/kauer/fred seems to be mounted read-only.
kauer at karl:~$ ls fred
autorun.inf  dists     md5sum.txt  preseed             usb-creator.exe
boot         install   pics        README.diskdefines  wubi.exe
casper       isolinux  pool        ubuntu
kauer at karl:~$ ls /mnt
blah

Regards, K.




> For example, my home directory is mounted separately so that any
> runaway experiments don't use up the disk space of other things, but
> if I have root do
>    mount --bind /home/kevin /mnt
>    ls /mnt
> I see the same thing as if I just did
>     ls /home/kevin
> 
> -- 
> Kevin O'Gorman
> 
> programmer, n. an organism that transmutes caffeine into software.
> 

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Karl Auer (kauer at biplane.com.au)
http://www.biplane.com.au/kauer
http://www.biplane.com.au/blog

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