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

Technical documentation

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semmns — number of System V IPC system-wide semaphores






Allowed values

Minimum: semmni

Maximum: 335534080


The semmns tunable specifies the maximum total individual System V IPC system-wide semaphores which can be assigned by applications. Semaphores are assigned in "sets" associated with an ID. Thus semaphores can be distributed in any manner across the range of IDs with one or more per ID.

There is no reason to specify semmns less than semmni (the maximum number of identifiers) as each ID requires at least one semaphore.

If an application attempts to create a semaphore set with more semaphores than are remaining, 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 applications require more total semaphores in the system.

When Should the Value of This Tunable Be Lowered?

If requirements for semaphores has decreased, or there is a need to hard-limit applications from acquiring larger numbers of 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 the semmns tunable does not require changes to other tunables.


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.


semmns was developed by AT&T.

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