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 (con-
       sult 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 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>

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,  Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                    MSGGET(3P)