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Tunable Kernel Parameters
HP-UX 11i Version 3: February 2007

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semume — maximum number of System V IPC undo entries per process






Allowed values

Minimum: 1

Maximum: semmns


The semume tunable specifies the maximum number of System V IPC semaphores upon which a single process can have outstanding (non-zero) "undo" operations.

If an application exhausts this limit, it will receive an EINVAL error from semop().

For more information about System V semaphores, refer to the Overview section of the sema(5) manpage.

Who Is Expected to Change This Tunable?


Restrictions on Changing

Changes to this tunable take effect at the next reboot.

When Should the Value of This Tunable Be Raised?

If applications require more semaphore undo operations per process.

When Should the Value of This Tunable Be Lowered?

If per-process requirements for semaphore operation has significantly decreased, or if there for limit protection on run-away applications which change semaphores.

What Other Tunable Values Should Be Changed at the Same Time?

All the System V semaphore tunables are interrelated and should not be treated as independent variables. The tunables must be evaluated as a system to ensure they reflect the application requirements. The semaphore tunables include semaem, semmni, semmns, semmnu, semmsl, semume, semvmx, and sysv_hash_locks. Typically, a change in semume does not require attention to other tunables. However, changes to semmsl or semmni might require changes to semume if individual application processes are expected to use fewer or more semaphores with "undo" semantics.


All HP-UX kernel tunable parameters are release specific. This parameter may be removed or have its meaning changed in future releases of HP-UX.

A two-dimensional table of undo structures (~8 bytes each) is allocated in kernel memory at boot time. This memory is reserved whether or not it is used.

The table dimensions are semume and semmnu (maximum number of per-process undo structures). So the memory requirement is approximately the product of those two tunables and the structure size. Use care when setting these two tunables, as they can have a profound effect on memory utilization, due to the multiplicative effect.

Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parameter values. After installation, some tunable parameters may no longer be at the default or recommended values. For information about the effects of installation on tunable values, consult the documentation for the kernel software being installed. For information about optional kernel software that was factory installed on your system, see HP-UX Release Notes at http://docs.hp.com.


semume was developed by AT&T.

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