hpux man page for shmmni

shmmni(5)							File Formats Manual							 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) mechanism.  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
       permissions 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 corresponds 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
       message.

   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 tun-
       able, 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 taking 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 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  tun-
       able  values,  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)