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, 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(P)