ipcs -- Command

Display a snapshot of interprocess communications
ipcs [-abcmopst] [-N kernel]

The command ipcs  prints information about interprocess communication (IPC)
objects.

Options

ipcs recognizes the following command-line options:

-a ``All'' print option; i.e., combine the options -b, -c, -o, -p, and -t.

-b ``Biggest'' option: Display the  maximum size that the kernel allows for
   each kind of IPC object.

-c Display the login  name and group name of the  user who created each IPC
   object.

-m Display  information  about shared-memory  segments.   By default,  ipcs
   displays information about all IPC objects.

-N kernel
   Read kernel-specific information from kernel instead of from the default
   kernel /autoboot.

-o ``Outstanding usage''  option: Display the number  of messages currently
   queued  and their  total  size in  bytes,  and the  number of  processes
   attached to each shared-memory segment.

-p Display the process identifiers of the following:

   -> The last process to send a message.
   -> The last process to receive a message on each message queue.
   -> Each creating process.
   -> The  last process  to  attach to  or detach  from each  shared-memory
      segment.

-q Display  information about  message queues.   By default,  ipcs displays
   information about all IPC objects.

-s Display information about sets of semaphores.  By default, ipcs displays
   information about all IPC objects.

-t Display the following information about times:

   -> When  functions msgsnd()  and msgrcv()  were  last executed  for each
      message queue.

   -> When the  functions shmat() and  shmdt() were last  executed for each
      shared-memory segment.

   -> When  the  function  semop()  was  last  executed  for  each  set  of
      semaphores.

Format of Displayed Information

The following names and describes  each column of information that ipcs can
display for each IPC object.   The letters in parentheses name the command-
line options tell  ipcs to display this column; all  means that ipcs always
displays this column:

ATIME (-at)
     The last time a process attached itself to this shared-memory segment.

CBYTES (-ao)
     The total number of bytes in this message queue.

CGROUP (-ac)
     The name of the group to which the creator of this IPC object belongs.

CPID (-ap)
     The identifier of the process that created this shared-memory segment.

CREATOR (-ac)
     The login identifier of the user who created this IPC object.

CTIME (-at)
     The time when this IPC object was created or last changed.

DTIME (-at)
     The most recent time a process detached itself from this shared-memory
     segment.

GROUP (all)
     The name of the group to which the owner of this IPC object belongs.

ID (all)
     The numeric identifier of this IPC object.

KEY (all)
     The  key that  names this  IPC object.  Applications  use this  key to
     identify and manipulate the IPC object.

LPID (-ap)
     The  identifier of  the last  process  to have  attached itself  to or
     detached itself from this shared-memory segment.

LRPID (-ap)
     The identifier  of the  last process to  have received a  message from
     this message queue.

LSPID (-ap)
     The identifier  of the  last process  to have sent  a message  to this
     message queue.

MODE (all)
     The IPC  object's mode.  The  mode is a  string of 11  characters that
     interprets the value of field mode in the structure ipc_perm, which is
     part of each IPC object.  (For more information on this structure, see
     the Lexicon  entries msgget(), semget(), and  shmget().) The first two
     mode characters are as follows:

     R  A process is waiting for msgrcv().
     S  A process is waiting for msgsnd().
     D  The associated shared-memory segment has been removed.
     C  The associated shared-memory segment will be cleared when the first
        process attaches itself to it.
     -  The corresponding flag is not set.

     The last nine  characters of the mode give the  permissions on the IPC
     object -- three sets of three characters each.  In each set, the first
     character marks whether read permission is granted, the second whether
     permission to write or alter is granted, and the third is unused.  The
     first set  gives the  permissions of the  user who created  the object
     (its ``owner'');  the second,  the permissions  of other users  in the
     owner's group; and the third, the permissions of all other users.

NATTCH (-ao)
     The number of processes attached to this shared-memory segment.

NSEMS (-ab)
     The number of semaphores in this set.

OTIME (.t)
     The last time a semaphore operation was completed on this set.

OWNER (all)
     The login identifier of the user who ``owns'' this IPC object.

QBYTES (-ab)
     The number of bytes left available to the messages in this queue.

QNUM (-ao)
     The number of messages in this queue.

RTIME (-at)
     The last time a message was received from this queue.

SEGSZ (-ab)
     The size of this shared-memory segment.

STIME (-at)
     The last time a message was sent to this queue.

T (all)
     The type of IPC object this is, as follows:

         m   Shared-memory segment
         q   Message queue
         s   Set of semaphores

See Also

commands,
ipcrm,
msgget(),
semget(),
shmget()

Notes

ipcs gives information about the way interprocess communications are at the
moment you run it.  The data it returns can change even as you read them.

© 2012 by Stephen A. Ness