msgmni.5 (2010 09)

m
msgmni(5) msgmni(5)
(Tunable Kernel Parameters)
NAME
msgmni - maximum number of system-wide System V IPC message queues (IDs) allowed
VALUES
Default
512
Failsafe
512
Allowed Values
Minimum: 1
Maximum: 1,000,000
DESCRIPTION
The msgmni tunable specifies the maximum number of system-wide System V IPC message queue
identifiers (one per queue). Each message queue created has an identifier (ID) and there is an upper
limit of msgmni identifiers.
Applications use the
msgget() system call to create new queues. If all IDs have been used,
msgget()
will return [ENOSPC].
If a process acquires a message queue, but the process terminates without removing it, the queue and all
its messages remain. Abandoned message queues can be removed with the
ipcrm command. Message
queue status can be monitored using the ipcs command.
For more information about System V message queues, refer to the Overview section of the mesg(5) man-
page.
Who Is Expected to Change This Tunable?
Anyone.
Restrictions on Changing
This tunable is dynamic. Changes to to this tunable take effect immediately.
When Should the Value of This Tunable Be Raised?
Raise this tunable when applications require more queues.
When Should the Value of This Tunable Be Lowered?
Lower this tunable when the requirement for queues has diminished.
What are the Side Effects of Lowering the Value?
Lowering the value increases the risk of application failure due to the inability to create more message
queues. Lowering the tunable has no effect on any active message queues, even if the new tunable value
is less than the number of queues created in the system. However, no new queues may be created until
the number of active queues falls below the setting of
msgmni.
What Other Tunable Values Should Be Changed at the Same Time?
All the System V message queue tunables are interrelated and should not be treated as independent vari-
ables. The set must be evaluated as a system to ensure the tunables reflect the application requirements.
The message tunables include
msgmbs, msgmnb, msgmni, and msgtql. Specifically, msgtql and
msgmbs tunables may need adjustment along with changes to the msgmni tunable.
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 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://www.hp.com/go/hpux-core-docs.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1