msgmap(5)                                                         msgmap(5)
                          Tunable Kernel Parameters



 NAME    [Toc]    [Back]
      msgmap - number of entries in the System V IPC message space resource
      map

 VALUES    [Toc]    [Back]
    Failsafe
      (2+msgtql)

    Default    [Toc]    [Back]
      (2+msgtql)

    Allowed values    [Toc]    [Back]
      Minimum: 3

      Maximum: msgtql+2 or msgseg+2, whichever is lower.

    Recommended Value    [Toc]    [Back]
      msgtql+2

 DESCRIPTION    [Toc]    [Back]
      The msgmap tunable specifies the size of (number of entries in) the
      message space resource map that tracks the free space in shared IPC
      message space.  Each resource map entry is an offset-space pair which
      points to the offset and size (bytes) of each contiguous series of
      unused message space "segments".

      If the map is full when message segments are released (e.g., by
      msgrcv()), the system issues the

           DANGER: mfree map overflow.

      warning message, and those segments will be left unusable.

      The msgtql tunable determines how many messages can exist.  At
      maximum, there can be one free range of segments between each real
      message.  So, there can be msgtql+1 free segment ranges.  One
      additional map entry is required for accounting information, so the
      recommended value for the msgmap tunable is msgtql+2.

      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 to this tunable take effect at the next reboot.

    When Should the Value of This Tunable Be Raised?
      Raise this tunable when the free-space map is full and the system
      issues the warning message



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






 msgmap(5)                                                         msgmap(5)
                          Tunable Kernel Parameters



           DANGER: mfree map overflow.

      A larger value for msgmap can correct this issue.

    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 msgmap tunable
      should be made whenever there are changes to the msgtql 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.

      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]
      msgmap was developed by AT&T.

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


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