msgmax(5)

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 EINVAL.

For more information about System V message queues, refer to the Overview section of the mesg(5) manpage.

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 variables. 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 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

msgmax was developed by AT&T.