semmni.5 (2010 09)

s
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()
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?
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 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 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 identifiers. Lowering the tunable has no effect on any
active semaphore identifiers, even if the new tunable value is less than the number of semaphore
identifiers already created on the system. However, no new semaphore identifiers may be created until
the number of active semaphore identifiers falls below the setting of
semmni.
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. 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.
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