semmns.5 (2010 09)

s
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
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?
Anyone.
Restrictions on Changing
Changes to this tunable take effect at the next reboot.
Note: If the DynSysVSem optional product bundle is installed then changes to this tunable take effect
immediately.
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 acquir-
ing larger numbers of semaphores.
What Are the Side Effects of Lowering the Value?
The following side effect applies only if the DynSysVSem optional product bundle is installed.
If DynSysVSem is installed, lowering the value of this tunable increases the risk of application failure
due to the inability to create more semaphore sets. Lowering the tunable has no effect on any active
semaphores in their respective sets, even if the new tunable value is less than the number of semaphores
already created on the system. However, no new semaphore sets may be created until the number of
active semaphores on the system falls below the setting of
semmns.
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 vari-
ables. 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 tun-
ables.
Note: If the DynSysVSem optional product bundle is installed then the
semmnu, semume, and
sysv_hash_locks tunables are ignored and have no effect.
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.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1