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 msgseg(5)                                                         msgseg(5)
                          Tunable Kernel Parameters

 NAME    [Toc]    [Back]
      msgseg - number of System V IPC message segments in the system

 VALUES    [Toc]    [Back]

    Failsafe    [Toc]    [Back]

    Allowed Values    [Toc]    [Back]
      Minimum: 1

      Maximum: 32767 or ((2^32-1)/msgssz), whichever is smaller.

      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 msgseg specifies the total number of "segments" of system-wide
      shared memory message storage space which is shared among all IPC
      message queues.

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

      Segments are only used to store messages larger than 64 bytes long.
      Messages smaller than or equal to 64 bytes long are stored in a
      different area and do not consume a segment.

      If applications have consumed all message segments, the msgsnd() call
      will block until segments become available or return [EAGAIN] if
      IPC_NOWAIT was specified.

      Messages larger than a single segment are allocated in a number of
      contiguous segments sufficient to hold the message.  As all segments
      are allocated as a table (contiguous memory), fragmentation can occur
      as messages are added and removed.  Therefore, if message sizes often
      exceed a single segment, consider allocating more segments than are
      actually needed for message data, to allow for some fragmentation.

      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.

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

 msgseg(5)                                                         msgseg(5)
                          Tunable Kernel Parameters

    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

    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 msgssz and msgtql tunables may
      need to be adjusted in conjunction with changes in the msgseg 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]
      msgmni was developed by AT&T.

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

 Hewlett-Packard Company            - 2 -      HP-UX 11i Version 2: Sep 2004
[ Back ]
 Similar pages
Name OS Title
shmseg HP-UX maximum number of System V shared memory segments per process
msgmni HP-UX maximum number of system-wide System V IPC message queues (IDs) allowed
msgssz HP-UX number of bytes in a System V IPC message segment
msgmap HP-UX number of entries in the System V IPC message space resource map
msgmnb HP-UX maximum number of bytes on a single System V IPC message queue
shmmni HP-UX number of System V shared memory segment identifiers in the system
semmni HP-UX number of System V IPC system-wide semaphore identifiers
msgtql HP-UX maximum number of System V IPC messages in the system at any time
semmns HP-UX number of System V IPC system-wide semaphores
inet6_rth_segments Tru64 Return the number of segments (addresses) in an IPv6 Routing header
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