*nix Documentation Project
·  Home
 +   man pages
·  Linux HOWTOs
·  FreeBSD Tips
·  *niX Forums

  man pages->HP-UX 11i man pages -> shmmni (5)              


 shmmni(5)                                                         shmmni(5)
                          Tunable Kernel Parameters

 NAME    [Toc]    [Back]
      shmmni - number of System V shared memory segment identifiers in the

 VALUES    [Toc]    [Back]
      400 identifiers

    Allowed values    [Toc]    [Back]
      Minimum: 3

      Maximum: 32768

 DESCRIPTION    [Toc]    [Back]
      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
      kernel.  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?

    Restrictions on Changing    [Toc]    [Back]
      Changes to this tunable take effect immediately.

      Attempting to lower shmmni below the current number of identifiers in
      use or below the current value of shmseg will result in an [EINVAL]
      error message.

      Attempts to raise the value of shmmni when insufficient memory is
      available to the kernel to create the needed structures will result in
      an [ENOMEM] error message.

    When Should the Value of This Tunable Be Raised?
      shmmni should be raised if users of System V shared memory are
      receiving the [ENOSPC] error message on shmget() 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.

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

 shmmni(5)                                                         shmmni(5)
                          Tunable Kernel Parameters

    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?
      shmmax and shmseg should be considered.  shmseg should be changed in
      the same manner as shmmni, 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.

      shmmax 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    [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

 AUTHOR    [Toc]    [Back]
      shmmni was developed by HP.

 SEE ALSO    [Toc]    [Back]
      shmem(5), shmmax(5), shmseg(5).

 Hewlett-Packard Company            - 2 -      HP-UX 11i Version 2: Sep 2004
[ Back ]
 Similar pages
Name OS Title
shmmax HP-UX maximum size (in bytes) for a System V shared memory segment
semmni HP-UX number of System V IPC system-wide semaphore identifiers
shmseg HP-UX maximum number of System V shared memory segments per process
ipcrm Tru64 Removes message queue, semaphore set, or shared memory identifiers
msgssz HP-UX number of bytes in a System V IPC message segment
shmget HP-UX get shared memory segment
shmget NetBSD get shared memory segment
shmget IRIX get shared memory segment identifier
shmget Linux allocates a shared memory segment
shmem HP-UX enable or disable System V shared memory
Copyright © 2004-2005 DeniX Solutions SRL
newsletter delivery service