1MSGGET(P)                  POSIX Programmer's Manual                 MSGGET(P)
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NAME

6       msgget - get the XSI message queue identifier
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SYNOPSIS

9       #include <sys/msg.h>
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11       int msgget(key_t key, int msgflg);
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DESCRIPTION

15       The msgget() function operates on XSI message queues (see the Base Def‐
16       initions volume of IEEE Std 1003.1-2001, Section 3.224, Message Queue).
17       It is unspecified whether this function interoperates with the realtime
18       interprocess communication facilities defined in Realtime .
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20       The msgget() function shall return the message queue identifier associ‐
21       ated with the argument key.
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23       A  message  queue identifier, associated message queue, and data struc‐
24       ture (see <sys/msg.h>), shall be created for the argument key if one of
25       the following is true:
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27        * The argument key is equal to IPC_PRIVATE.
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29        * The  argument  key  does not already have a message queue identifier
30          associated with it, and (msgflg & IPC_CREAT) is non-zero.
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32       Upon creation, the data structure associated with the new message queue
33       identifier shall be initialized as follows:
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35        * msg_perm.cuid,  msg_perm.uid,  msg_perm.cgid, and msg_perm.gid shall
36          be set equal to the  effective  user  ID  and  effective  group  ID,
37          respectively, of the calling process.
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39        * The low-order 9 bits of msg_perm.mode shall be set equal to the low-
40          order 9 bits of msgflg.
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42        * msg_qnum, msg_lspid, msg_lrpid, msg_stime, and  msg_rtime  shall  be
43          set equal to 0.
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45        * msg_ctime shall be set equal to the current time.
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47        * msg_qbytes shall be set equal to the system limit.
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RETURN VALUE

50       Upon  successful completion, msgget() shall return a non-negative inte‐
51       ger, namely a message queue identifier. Otherwise, it shall  return  -1
52       and set errno to indicate the error.
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ERRORS

55       The msgget() function shall fail if:
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57       EACCES A  message  queue  identifier  exists  for the argument key, but
58              operation permission as specified by the  low-order  9  bits  of
59              msgflg  would not be granted; see XSI Interprocess Communication
60              .
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62       EEXIST A message queue identifier  exists  for  the  argument  key  but
63              ((msgflg & IPC_CREAT) && (msgflg & IPC_EXCL)) is non-zero.
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65       ENOENT A  message  queue identifier does not exist for the argument key
66              and (msgflg & IPC_CREAT) is 0.
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68       ENOSPC A message queue identifier is to  be  created  but  the  system-
69              imposed  limit  on  the  maximum number of allowed message queue
70              identifiers system-wide would be exceeded.
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73       The following sections are informative.
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EXAMPLES

76       None.
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APPLICATION USAGE

79       The POSIX Realtime Extension defines alternative interfaces for  inter‐
80       process communication (IPC). Application developers who need to use IPC
81       should design their applications so that modules using the IPC routines
82       described  in  XSI Interprocess Communication can be easily modified to
83       use the alternative interfaces.
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RATIONALE

86       None.
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FUTURE DIRECTIONS

89       None.
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SEE ALSO

92       XSI Interprocess Communication , Realtime , mq_close() , mq_getattr() ,
93       mq_notify()  ,  mq_open()  ,  mq_receive() , mq_send() , mq_setattr() ,
94       mq_unlink() , msgctl() , msgrcv() , msgsnd()  ,  the  Base  Definitions
95       volume of IEEE Std 1003.1-2001, <sys/msg.h>
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98       Portions  of  this text are reprinted and reproduced in electronic form
99       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
100       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
101       Specifications Issue 6, Copyright (C) 2001-2003  by  the  Institute  of
102       Electrical  and  Electronics  Engineers, Inc and The Open Group. In the
103       event of any discrepancy between this version and the original IEEE and
104       The  Open Group Standard, the original IEEE and The Open Group Standard
105       is the referee document. The original Standard can be  obtained  online
106       at http://www.opengroup.org/unix/online.html .
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110IEEE/The Open Group                  2003                            MSGGET(P)
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