NAME
shmseg — maximum number of System V shared memory segments per process
VALUES
Allowed values
Minimum: 1
Maximum: Any value less than or equal to
shmmni.
DESCRIPTION
Shared memory is an efficient InterProcess Communications (IPC) mechanism.
One process creates a shared memory segment and attaches it to its
address space.
Any processes looking to communicate with this process through the
shared memory segment then attach the shared memory segment to their
corresponding address spaces.
Once attached, a process can read from or write to the segment
depending on the permissions specified while attaching it.
This tunable sets an upper limit to the number of segments which can
be attached per process.
Who is Expected to Change This Tunable?
Anyone.
Restrictions on Changing
Changes to this tunable take effect immediately.
When Should the Value of This Tunable Be Raised?
If user processes reach their limit, more segments are desired,
and the current value is less than the total number of segments
in the system
(shmmni).
What Are the Side Effects of Raising the Value?
A single process will be able to acquire more segments, possibly
starving another process which previously was able to acquire
all the segments it needed.
In this case,
shmmni
should be raised if it is below it's maximum.
When Should the Value of This Tunable Be Lowered?
This tunable should only be lowered to enforce segment policy
on user processes, or if one runaway process is hogging the
global-segment pool.
Otherwise, keeping the maximum higher than the common usage
is harmless.
What Are the Side Effects of Lowering the Value?
None.
What Other Tunable Values Should Be Changed at the Same Time?
shmmni
should be considered, as previously described.
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.
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
shmseg
was developed by HP.
Printable version
