Re: Prevent umounting

["Stephen Samuel (gmail)" <darkonc@xxxxxxxxx>]

If you want to keep people from unmounting, create a file:
/mnt/my_file_system/tmp/TMPxxxxxx

then unlink that file, but do not close your open file descriptor.

The name will disappear but the  inode will continue to exist. As long as your program keeps the file descriptor for the unlinked file open, users will be unable to unmount the filesystem 


A simple example:
touch /media/disk-1/nothinge 
tail -f /media/disk-1/nothing& 
rm /media/disk-1/nothing

umount /media/disk-1
eject /media/disk-1
#  (both the last two commands should fail)..

kill %%  
# kill the background 'tail' process
eject /media/disk-1 
# that last 'eject' should work

On Sun, Jun 14, 2009 at 11:46 AM, Christian Kujau <lists@xxxxxxxxxxxxxxx> wrote:

[Cc'ing ext3-users again]

On Sun, 14 Jun 2009, Donato Capitella wrote:
> Well, that's not it.
>
> I modified the ext3 fs and added a kernel thread that performs deferred
> operations. As long as this thread is working, I would like the file
> system not to be unmounted.

I still don't understand the reasoning here: "not to be unmounted" as in
a permission-bound issue ("is not allowed to unmount") or a technical
issue? For the latter: simply keep an open file on the filesystem, unmount
will fail with -EBUSY. Or it's a matter of "because we can", as in
"because I want to be able to disallow mounting on the filesystem level".

But then again, I did not have my coffee yet and my brain keeps asking
why, why, why? :)

Christian.
--
BOFH excuse #202:

kernel panic: write-only-memory (/dev/wom0) capacity exceeded.

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-- 
Stephen Samuel http://www.bcgreen.com  Software, like love, 
778-861-7641                              grows when you give it away

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