NAME
semmnu — maximum number of System V IPC undo structures for processes
VALUES
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 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
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 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
http://docs.hp.com.
AUTHOR
semmnu
was developed by AT&T.
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