msgmnb.5 (2010 09)

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msgmnb(5) msgmnb(5)

(Tunable Kernel Parameters)

NAME

msgmnb - maximum number of bytes on a single System V IPC message queue

VALUES

Default

16384

Failsafe

16384

Allowed Values

Minimum: 0

Maximum: 0x4000000

DESCRIPTION

The msgmnb tunable speciﬁes the maximum allowable total combined size, in bytes, of all messages

queued in a single given System V IPC message queue at any one time.

If a

msgsnd() system call attempts to exceed the limit imposed by

msgmnb, it will block (or return

[EAGAIN] if

IPC_NOWAIT was speciﬁed) until a caller of

msgrcv() decreases the number of bytes in

the queue sufﬁciently such that the new message, along with other messages still on the queue, will ﬁt

within the

msgmnb limit.

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 affect subsequent

msgsnd() operations.

When Should the Value of This Tunable Be Raised?

Raise this tunable if applications have a need to store more data on a single queue.

When Should the Value of This Tunable Be Lowered?

Lower this tunable when applications have no need to store large amounts of data on a single queue.

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

msgmnb, msgmni, msgmbs, and msgtql. Speciﬁcally, when the

msgmnb

tunable is changed, adjustments may also be needed to the msgmbs and msgtql 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.

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

AUTHOR

msgmnb was developed by AT&T.