HP-UX Reference (11i v2 04/09) - 5 Miscellaneous Topics (vol 9)

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msgmax(5) msgmax(5)

(Tunable Kernel Parameters)

NAME

msgmax - maximum System V IPC message size in bytes

VALUES

Default

8192

Failsafe

8192

Allowed values

Minimum: 0

Maximum: (64*1024*1024), (msgssz*msgseg

), or msgmnb, whichever is smaller.

DESCRIPTION

The

msgmax tunable speciﬁes the maximum allowable size, in bytes, of any single message in a System V

message queue. msgmax must be no larger than

msgmnb (the size of a queue) nor can it be larger than

the preallocated system-wide message storage space (

msgssz*msgseg

Possible strategies for deciding this tunable value include setting it equal to

msgmnb (one message per

queue) or the size of the biggest expected message which is less than

msgmnb.

Any

msgsnd() system call that attempts to send a message larger than msgmax bytes will return [EIN-

VAL].

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

Changes affect subsequent

msgsnd() operations.

When Should the Value of This Tunable Be Raised?

Raise this tunable when applications need to send larger messages.

When Should the Value of This Tunable Be Lowered?

Lower this tunable when applications are only using smaller message sizes.

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

msgmap, msgmax, msgmnb, msgmni, msgseg, msgssz, and msgtql.

Speciﬁcally, changes to the msgmax tunable may also require changes to the msgmnb, msgssz, and

msgseg 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://docs.hp.com.

AUTHOR

msgmax was developed by AT&T.