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

       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.

       msgget — get the XSI message queue identifier

       #include <sys/msg.h>

       int msgget(key_t key, int msgflg);

       The msgget() function operates on XSI message queues (see the Base Def‐
       initions	 volume of POSIX.1‐2008, Section 3.225, Message Queue).	 It is
       unspecified whether  this  function  interoperates  with	 the  realtime
       interprocess communication facilities defined in Section 2.8, 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  to	the  effective user ID and effective group ID, respec‐
	   tively, of the calling process.

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

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

	*  msg_ctime shall be set to the current time, as described in Section
	   2.7.1, IPC General Description.

	*  msg_qbytes shall be set to the system limit.

       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.

       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 Section 2.7, XSI Interprocess

       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.


       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 Section 2.7, XSI Interprocess Communication can be easily
       modified to use the alternative interfaces.



       Section 2.7, XSI Interprocess  Communication,  Section  2.8,  Realtime,
       ftok(), mq_close(), mq_getattr(), mq_notify(), mq_open(), mq_receive(),
       mq_send(), mq_setattr(), mq_unlink(), msgctl(), msgrcv(), msgsnd()

       The Base Definitions volume of  POSIX.1‐2008,  Section  3.225,  Message
       Queue, <sys_msg.h>

       Portions	 of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       --  Portable  Operating	System	Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
       cal  and	 Electronics  Engineers,  Inc  and  The	 Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum	 1  applied.)  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 .

       Any typographical or formatting errors that appear  in  this  page  are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors,	 see  https://www.ker‐ .

IEEE/The Open Group		     2013			    MSGGET(3P)

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