HP-UX Reference (11i v2 07/12) - 5 Miscellaneous (vol 9)
s
semmnu(5) semmnu(5)
(Tunable Kernel Parameters)
NAME
semmnu - maximum number of System V IPC undo structures for processes
VALUES
Failsafe
256
Default
256
Allowed values
Minimum: 1
Maximum: (nproc-4)
DESCRIPTION
The semmnu tunable specifies the maximum number of System V IPC system-wide processes that can
have "undo" operations pending at any given time.
If an application exhausts this limit, it will receive an [ENOSPC] 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.
When Should the Value of This Tunable Be Raised?
When the set of application processes which use semaphore "undo" semantics exceeds the limit.
When Should the Value of This Tunable Be Lowered?
If requirements for semaphore "undo" semantics has significantly decreased, or for limiting protection 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 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. Generally, a change in
semmnu does not require attention to other tunables.
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.
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
semmnu was developed by AT&T.
HP-UX 11i Version 2: December 2007 Update − 1 − Hewlett-Packard Company 409