Re: Mandatory File Locking

Yeah it should work supposedly but its not working. For reference I'm
attaching a sample file may be I am doing something very wrong.
I make executable of attached code. Then run one instance on terminal & 2nd
on another terminal.
Executable on 2nd terminal is able to write in the file.


Regards,
~Nishant

On Sat, Nov 22, 2008 at 12:56 AM, Mark Haney <mhaney@xxxxxxxxxxxxxxxx>wrote:

test test wrote:
Hello,



I need to put a mandatory lock on /dev/fb0 (presently any file) in Linux
OS.
But in actual scenario it will be a device file.



OS: Ubuntu Hardy Heron 8.04



Scenario:

1. Process A is super process (controller).

2. Process B is normal process.

3. *Process A and B are non-cooperating process, they simple don't know
about other process existence and they are not interested in knowing it
either.(So, advisory locking is out of scope). *

4. At particular instance Process B is accessing /dev/fb0.

5. Now, Process A wants access to it.

6. Process A locks /dev/fb0

7. It can hold the lock as long it wants & in any case process B cannot
write anything to it. (It's better if B cannot read the contents also).



I also changed permissions of directory and lock file.



I used:

chmod g-x test

chmod g+s test



http://www.hackinglinuxexposed.com/articles/20030623.html

That was a quick google on file locking in Linux. Are you coding these
processes yourself? I mean there are documented ways of locking files
programmatically in linux as well.

Based on what you posted the file locking should work. Are you saying
it doesn't?





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Mark Haney
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Call (866) ERC-7110 for after hours support

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