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 msgssz(5)                                                         msgssz(5)
                          Tunable Kernel Parameters

 NAME    [Toc]    [Back]
      msgssz - number of bytes in a System V IPC message segment

 VALUES    [Toc]    [Back]

    Failsafe    [Toc]    [Back]

    Allowed Values    [Toc]    [Back]
      Minimum: 65

      Maximum: (2^32-1)/msgseg

      The product of msgseg*msgssz must not exceed a 32 bit integer value of
      4,294,967,295 (2^32)-1.

 DESCRIPTION    [Toc]    [Back]
      The msgssz tunable specifies the size, in bytes, of a "segment" of
      memmory space reserved for storing IPC messages.  Space for messages
      is acquired in segment-sized increments as required to contain the
      message.  Separate messages do not share segments.  Messages of size
      less than or equal to 64 bytes are allocated in a different area and
      do not require a segment.

      The total available space for messages greater than 64 bytes in size
      on the system is defined by the product of msgseg*msgssz, the number
      of segments multiplied by the segment size.

      It is best to select a segment size equal to the size of most messages
      sent by applications.  This ensures optimal memory utilization of the

      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?

    Restrictions on Changing    [Toc]    [Back]
      Changes to this tunable take effect at the next reboot.

    When Should the Value of This Tunable Be Raised?
      Raise this tunable if applications block too frequently in msgsnd(),
      requiring more or larger messages be held in the kernel message

    When Should the Value of This Tunable Be Lowered?
      Lower this tunable when applications no longer require as much message

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

 msgssz(5)                                                         msgssz(5)
                          Tunable Kernel Parameters

    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, the msgseg and msgtql tunables may
      need to be adjusted in conjunction with changes in the msgssz tunable.

 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.  The 64 byte threshold may change in future
      releases of HP-UX.

      A table of message segments is allocated in kernel memory at boot
      time.  This memory is reserved whether or not it is used.

      The memory requirement is the product the msgssz and msgseg tunables.
      Use care when setting these two tunables, as they can have a profound
      effect on memory utilization, due to the multiplicative effect.

      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

 AUTHOR    [Toc]    [Back]
      msgssz was developed by AT&T.

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

 Hewlett-Packard Company            - 2 -      HP-UX 11i Version 2: Sep 2004
[ Back ]
 Similar pages
Name OS Title
msgmnb HP-UX maximum number of bytes on a single System V IPC message queue
shmmax HP-UX maximum size (in bytes) for a System V shared memory segment
msgdsize Tru64 STREAMS: Returns the number of bytes in a message
adjmsg Tru64 STREAMS: Removes the specified number of bytes from a message
shmmni HP-UX number of System V shared memory segment identifiers in the system
msgmax HP-UX maximum System V IPC message size in bytes
maxdsiz HP-UX maximum size (in bytes) of the data segment for any user process
maxtsiz HP-UX maximum size (in bytes) of the text segment for any user process
maxdsiz_64bit HP-UX maximum size (in bytes) of the data segment for any user process
maxtsiz_64bit HP-UX maximum size (in bytes) of the text segment for any user process
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