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

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semmni(5) semmni(5)

(Tunable Kernel Parameters)

NAME

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

VALUES

Failsafe

2048

Default

2048

Allowed values

Minimum: 2

Maximum: semmns.

DESCRIPTION

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() sys-

tem 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?

Anyone.

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 appli-

cations 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 sema-

phore 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.

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

semmni was developed by AT&T.