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MSGGET(3P)                 POSIX Programmer's Manual                MSGGET(3P)

PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
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 Def-
       initions 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 associ-
       ated with the argument key.
       A message queue identifier, associated message queue, and  data  struc-
       ture (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  inte-
       ger,  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 inter-
       process 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>
COPYRIGHT
       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 .

IEEE/The Open Group                  2003                           MSGGET(3P)