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

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semmni — number of System V IPC system-wide semaphore identifiers






Allowed values

Minimum: 2

Maximum: semmns.


The semmni tunable specifies the maximum number of System V IPC system-wide semaphore sets (and identifiers) which can exist at any given time. A single identifier (ID) is returned for each semget() system call to create a new set of one or more (up to semmsl) semaphores.

If an application attempts to create a semaphore set when all IDs have previously been allocated, it will receive an ENOSPC error from semget().

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 there is a requirement of more total unique semaphore IDs in the system, or one or more applications require more semaphore IDs. There is no reason to specify more system-wide identifiers than the total of the semmns semaphores.

When Should the Value of This Tunable Be Lowered?

If requirements for semaphore sets (IDs) has significantly decreased, or there is a need to hard-limit applications from acquiring larger numbers of semaphore IDs.

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. Specifically, changes in the semmni tunable may also require changes in the semmns tunable. Very significant changes in semmni may also require changes in the sysv_hash_locks tunable.


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.

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.


semmni was developed by AT&T.

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