msgmax(5)                                                         msgmax(5)
                          Tunable Kernel Parameters



 NAME    [Toc]    [Back]
      msgmax - maximum System V IPC message size in bytes

 VALUES    [Toc]    [Back]
    Default
      8192

    Failsafe    [Toc]    [Back]
      8192

    Allowed values    [Toc]    [Back]
      Minimum: 0

      Maximum: (64*1024*1024), (msgssz*msgseg), or  msgmnb, whichever is
      smaller.

 DESCRIPTION    [Toc]    [Back]
      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    [Toc]    [Back]
      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



 Hewlett-Packard Company            - 1 -      HP-UX 11i Version 2: Sep 2004






 msgmax(5)                                                         msgmax(5)
                          Tunable Kernel Parameters



      also require changes to the msgmnb, msgssz, and msgseg tunables.

 WARNINGS    [Toc]    [Back]
      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    [Toc]    [Back]
      msgmax was developed by AT&T.

 SEE ALSO    [Toc]    [Back]
      msgsnd(2), mesg(5), msgmap(5), msgmnb(5), msgmni(5), msgseg(5),
      msgssz(5), msgtql(5).


 Hewlett-Packard Company            - 2 -      HP-UX 11i Version 2: Sep 2004