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shmmni(5)							     shmmni(5)

NAME
       shmmni  -  number  of System V shared memory segment identifiers in the
       system

VALUES
   Default
   Allowed values
DESCRIPTION
       Shared memory is an efficient InterProcess Communications (IPC)	mecha‐
       nism.   One  process creates a shared memory segment and attaches it to
       its address space.  Any processes  looking  to  communicate  with  this
       process through the shared memory segment then attach the shared memory
       segment to their corresponding address spaces as well.  Once  attached,
       a  process  can read from or write to the segment depending on the per‐
       missions specified while attaching it.

       This tunable effectively sets the number of unique  segments  creatable
       system  wide,  since each segment is assigned an identifier by the ker‐
       nel.  The identifier is simply a reference generated by the kernel such
       that any user process can request a particular segment for sharing with
       a simple integer, and let the kernel determine which segment this  cor‐
       responds to.

   Who is Expected to Change This Tunable?
       Anyone.

   Restrictions on Changing
       Changes to this tunable take effect immediately.

       Attempting  to  lower below the current number of identifiers in use or
       below the current value of will result in an error message.

       Attempts to raise the value of when insufficient memory is available to
       the kernel to create the needed structures will result in an error mes‐
       sage.

   When Should the Value of This Tunable Be Raised?
       should be raised if users of System V shared memory are	receiving  the
       error message on calls.

   What Are the Side Effects of Raising the Value?
       Kernel  memory usage will be slightly increased, as the data structures
       used to track the segments are allocated based on this tunable.

   When Should the Value of This Tunable Be Lowered?
       If kernel memory is at a premium, or it is known that few segments will
       be needed, a slight savings can be gained from decreasing this tunable,
       and thus decreasing the data structure memory usage associated with it.

   What Are the Side Effects of Lowering the Value?
       Kernel memory usage will be slightly reduced.

   What Other Tunable Values Should Be Changed at the Same Time?
       and should be considered.  should be changed  in	 the  same  manner  as
       since  lowering	the  total  number  of segments but raising the number
       available per process only makes sense if you want a few processes tak‐
       ing all the segments.

       is  more	 complex  and  any  changes  to it really depend on the effect
       desired.	 Refer to the shmmax(5) manpage for  more  information	before
       changing this tunable.

WARNINGS
       All HP-UX kernel tunable parameters are release specific.  This parame‐
       ter 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 val‐
       ues.  For information about the effects of installation on tunable val‐
       ues, consult the documentation for the kernel software being installed.
       For  information	 about	optional  kernel  software  that  was  factory
       installed on your system, see at

AUTHOR
       was developed by HP.

SEE ALSO
       shmem(5), shmmax(5), shmseg(5).

			   Tunable Kernel Parameters		     shmmni(5)

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