semume.5 (2010 09)

s
semume(5) semume(5)
(Tunable Kernel Parameters)
NAME
semume - maximum number of System V IPC undo entries per process
VALUES
Failsafe
100
Default
100
Allowed values
Minimum: 1
Maximum: semmns
DESCRIPTION
Note: If the DynSysVSem optional product bundle is installed then this tunable is ignored and has no
effect. Applications can perform "undo" operations without any system imposed limits.
The
semume tunable specifies the maximum number of System V IPC semaphores upon which a single
process can have outstanding (non-zero) "undo" operations.
If an application exhausts this limit, it will receive an [EINVAL] error from
semop().
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 are ignored
and have no effect.
When Should the Value of This Tunable Be Raised?
If applications require more semaphore undo operations per process.
When Should the Value of This Tunable Be Lowered?
If per-process requirements for semaphore operation has significantly decreased, or if there for limit pro-
tection on run-away applications which change 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 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 semume does not require attention to other tunables. How-
ever, changes to semmsl or semmni might require changes to semume if individual application
processes are expected to use fewer or more semaphores with "undo" semantics.
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.
A two-dimensional table of undo structures (˜8 bytes each) is allocated in kernel memory at boot time.
This memory is reserved whether or not it is used.
The table dimensions are
semume and semmnu (maximum number of per-process undo structures). So
the memory requirement is approximately the product of those two tunables and the structure size. Use
care when setting these two tunables, as they can have a profound effect on memory utilization, due to
the multiplicative effect.
Note: If the DynSysVSem optional product bundle is installed then
semume and semmnu are ignored
and have no effect. No memory is allocated at boot time. Instead "undo" structures are dynamically
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1