HP-UX Reference (11i v3 07/02) - 5 Miscellaneous Topics (vol 9)

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semmns(5) semmns(5)

(Tunable Kernel Parameters)

NAME

semmns - number of System V IPC system-wide semaphores

VALUES

Failsafe

4096

Default

4096

Allowed values

Minimum: semmni

Maximum: 335534080

DESCRIPTION

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 sema-

phores 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?

Anyone.

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 sema-

phore 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 tun-

ables.

WARNINGS

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 parame-

ter 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.

AUTHOR

semmns was developed by AT&T.