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NAME
       msgget - get the XSI message queue identifier


SYNOPSIS
       #include <sys/msg.h>

       int msgget(key_t key, int msgflg);


DESCRIPTION
       The   msgget()   function   operates   on  XSI  message  queues  (see  the  Base  Definitions  volume  of
       IEEE Std 1003.1-2001,  Section  3.224,  Message  Queue).  It  is  unspecified   whether   this   function
       interoperates with the realtime interprocess communication facilities defined in Realtime .

       The msgget() function shall return the message queue identifier associated with the argument key.

       A  message  queue  identifier,  associated  message queue, and data structure (see <sys/msg.h>), shall be
       created for the argument key if one of the following is true:

        * The argument key is equal to IPC_PRIVATE.

        * The argument key does not already have a message queue identifier associated with it,  and  (msgflg  &
          IPC_CREAT) is non-zero.

       Upon  creation,  the data structure associated with the new message queue identifier shall be initialized
       as follows:

        * msg_perm.cuid, msg_perm.uid, msg_perm.cgid, and msg_perm.gid shall be set equal to the effective  user
          ID and effective group ID, respectively, of the calling process.

        * The low-order 9 bits of msg_perm.mode shall be set equal to the low-order 9 bits of msgflg.

        * msg_qnum, msg_lspid, msg_lrpid, msg_stime, and msg_rtime shall be set equal to 0.

        * msg_ctime shall be set equal to the current time.

        * msg_qbytes shall be set equal to the system limit.


RETURN VALUE
       Upon  successful  completion,  msgget()  shall  return  a  non-negative  integer,  namely a message queue
       identifier. Otherwise, it shall return -1 and set errno to indicate the error.


ERRORS
       The msgget() function shall fail if:

       EACCES A message queue identifier exists for the argument key, but operation permission as  specified  by
              the low-order 9 bits of msgflg would not be granted; see XSI Interprocess Communication .

       EEXIST A  message  queue  identifier  exists  for the argument key but ((msgflg & IPC_CREAT) && (msgflg &
              IPC_EXCL)) is non-zero.

       ENOENT A message queue identifier does not exist for the argument key and (msgflg & IPC_CREAT) is 0.

       ENOSPC A message queue identifier is to be created but the system-imposed limit on the maximum number  of
              allowed message queue identifiers system-wide would be exceeded.

       The following sections are informative.


EXAMPLES
       None.


APPLICATION USAGE
       The  POSIX  Realtime  Extension  defines  alternative  interfaces  for  interprocess communication (IPC).
       Application developers who need to use IPC should design their applications so that modules using the IPC
       routines  described  in  XSI  Interprocess  Communication  can  be easily modified to use the alternative
       interfaces.


RATIONALE
       None.


FUTURE DIRECTIONS
       None.


SEE ALSO
       XSI Interprocess Communication , Realtime ,  mq_close()  ,  mq_getattr()  ,  mq_notify()  ,  mq_open()  ,
       mq_receive()  ,  mq_send()  ,  mq_setattr()  ,  mq_unlink()  ,  msgctl() , msgrcv() , msgsnd() , the Base
       Definitions volume of IEEE Std 1003.1-2001, <sys/msg.h>


       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
       Inc  and  The  Open Group. In the event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard  is  the  referee  document.  The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .