[Beowulf] Shared memory and semaphores

Bill Wichser bill at Princeton.EDU
Thu Jul 8 09:35:56 PDT 2004

When user programs end either due to a crash or sometimes even 
naturally, both shared memory segments and semaphores are being left 
behind on our dual processor Xeon nodes.  Since users have no access to 
the nodes, the cleanipcs script will not function for them as this needs 
rsh/ssh access.

Shared memory segments are easy.  One can run a script checking for user 
segments and if the NATTCH field is zero, they can be removed.  The 
problem is in determining if the semaphores are no longer needed.

Since these are dual processor machines under PBS control, another job, 
started by the same user, could become active before checks can be done 
and removals start happening.

Is there a test for semaphores to determine if they are inactive?  How 
can I determine if one can safely be removed?



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