1MSGGET(3P)                 POSIX Programmer's Manual                MSGGET(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
10

NAME

12       msgget — get the XSI message queue identifier
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SYNOPSIS

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

20       The msgget() function operates on XSI message queues (see the Base Def‐
21       initions  volume of POSIX.1‐2017, Section 3.226, Message Queue).  It is
22       unspecified whether  this  function  interoperates  with  the  realtime
23       interprocess communication facilities defined in Section 2.8, Realtime.
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25       The msgget() function shall return the message queue identifier associ‐
26       ated with the argument key.
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28       A message queue identifier, associated message queue, and  data  struc‐
29       ture (see <sys/msg.h>), shall be created for the argument key if one of
30       the following is true:
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32        *  The argument key is equal to IPC_PRIVATE.
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34        *  The argument key does not already have a message  queue  identifier
35           associated with it, and (msgflg & IPC_CREAT) is non-zero.
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37       Upon creation, the data structure associated with the new message queue
38       identifier shall be initialized as follows:
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40        *  msg_perm.cuid, msg_perm.uid, msg_perm.cgid, and msg_perm.gid  shall
41           be  set  to  the  effective user ID and effective group ID, respec‐
42           tively, of the calling process.
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44        *  The low-order 9 bits of msg_perm.mode shall be set to the low-order
45           9 bits of msgflg.
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47        *  msg_qnum,  msg_lspid,  msg_lrpid, msg_stime, and msg_rtime shall be
48           set to 0.
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50        *  msg_ctime shall be set to the current time, as described in Section
51           2.7.1, IPC General Description.
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53        *  msg_qbytes shall be set to the system limit.
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RETURN VALUE

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

61       The msgget() function shall fail if:
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63       EACCES A  message  queue  identifier  exists  for the argument key, but
64              operation permission as specified by the  low-order  9  bits  of
65              msgflg  would  not be granted; see Section 2.7, XSI Interprocess
66              Communication.
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68       EEXIST A message queue identifier  exists  for  the  argument  key  but
69              ((msgflg & IPC_CREAT) && (msgflg & IPC_EXCL)) is non-zero.
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71       ENOENT A  message  queue identifier does not exist for the argument key
72              and (msgflg & IPC_CREAT) is 0.
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74       ENOSPC A message queue identifier is to  be  created  but  the  system-
75              imposed  limit  on  the  maximum number of allowed message queue
76              identifiers system-wide would be exceeded.
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78       The following sections are informative.
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EXAMPLES

81       None.
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APPLICATION USAGE

84       The POSIX Realtime Extension defines alternative interfaces for  inter‐
85       process communication (IPC). Application developers who need to use IPC
86       should design their applications so that modules using the IPC routines
87       described  in Section 2.7, XSI Interprocess Communication can be easily
88       modified to use the alternative interfaces.
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RATIONALE

91       None.
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FUTURE DIRECTIONS

94       None.
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SEE ALSO

97       Section 2.7, XSI Interprocess  Communication,  Section  2.8,  Realtime,
98       ftok(), mq_close(), mq_getattr(), mq_notify(), mq_open(), mq_receive(),
99       mq_send(), mq_setattr(), mq_unlink(), msgctl(), msgrcv(), msgsnd()
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101       The Base Definitions volume of  POSIX.1‐2017,  Section  3.226,  Message
102       Queue, <sys_msg.h>
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105       Portions  of  this text are reprinted and reproduced in electronic form
106       from IEEE Std 1003.1-2017, Standard for Information Technology --  Por‐
107       table  Operating System Interface (POSIX), The Open Group Base Specifi‐
108       cations Issue 7, 2018 Edition, Copyright (C) 2018 by the  Institute  of
109       Electrical  and  Electronics Engineers, Inc and The Open Group.  In the
110       event of any discrepancy between this version and the original IEEE and
111       The  Open Group Standard, the original IEEE and The Open Group Standard
112       is the referee document. The original Standard can be  obtained  online
113       at http://www.opengroup.org/unix/online.html .
114
115       Any  typographical  or  formatting  errors that appear in this page are
116       most likely to have been introduced during the conversion of the source
117       files  to  man page format. To report such errors, see https://www.ker‐
118       nel.org/doc/man-pages/reporting_bugs.html .
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122IEEE/The Open Group                  2017                           MSGGET(3P)
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