Tunable Kernel Parameters
NAME [Toc] [Back]
semmnu - maximum number of System V IPC undo structures for processes
VALUES [Toc] [Back]
Default [Toc] [Back]
Allowed values [Toc] [Back]
DESCRIPTION [Toc] [Back]
The semmnu tunable specifies the maximum number of System V IPC
system-wide processes that can have "undo" operations pending at any
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?
Restrictions on Changing [Toc] [Back]
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
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
semaphore 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 [Toc] [Back]
All HP-UX kernel tunable parameters are release specific. This
Hewlett-Packard Company - 1 - HP-UX 11i Version 2: Sep 2004
Tunable Kernel Parameters
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 perprocess
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 parameter 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
AUTHOR [Toc] [Back]
semmnu was developed by AT&T.
SEE ALSO [Toc] [Back]
semop(2), sema(5), semaem(5), semmns(5), semmni(5), semmsl(5),
semume(5), semvmx(5), sysv_hash_locks(5).
Hewlett-Packard Company - 2 - HP-UX 11i Version 2: Sep 2004 [ Back ]