1MSGGET(3P) POSIX Programmer's Manual MSGGET(3P)
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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.
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13 msgget — get the XSI message queue identifier
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16 #include <sys/msg.h>
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18 int msgget(key_t key, int msgflg);
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21 The msgget() function operates on XSI message queues (see the Base Def‐
22 initions volume of POSIX.1‐2008, Section 3.225, Message Queue). It is
23 unspecified whether this function interoperates with the realtime
24 interprocess communication facilities defined in Section 2.8, Realtime.
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26 The msgget() function shall return the message queue identifier associ‐
27 ated with the argument key.
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29 A message queue identifier, associated message queue, and data struc‐
30 ture (see <sys/msg.h>), shall be created for the argument key if one of
31 the following is true:
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33 * The argument key is equal to IPC_PRIVATE.
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35 * The argument key does not already have a message queue identifier
36 associated with it, and (msgflg & IPC_CREAT) is non-zero.
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38 Upon creation, the data structure associated with the new message queue
39 identifier shall be initialized as follows:
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41 * msg_perm.cuid, msg_perm.uid, msg_perm.cgid, and msg_perm.gid shall
42 be set to the effective user ID and effective group ID, respec‐
43 tively, of the calling process.
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45 * The low-order 9 bits of msg_perm.mode shall be set to the low-order
46 9 bits of msgflg.
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48 * msg_qnum, msg_lspid, msg_lrpid, msg_stime, and msg_rtime shall be
49 set to 0.
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51 * msg_ctime shall be set to the current time, as described in Section
52 2.7.1, IPC General Description.
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54 * msg_qbytes shall be set to the system limit.
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57 Upon successful completion, msgget() shall return a non-negative inte‐
58 ger, namely a message queue identifier. Otherwise, it shall return −1
59 and set errno to indicate the error.
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62 The msgget() function shall fail if:
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64 EACCES A message queue identifier exists for the argument key, but
65 operation permission as specified by the low-order 9 bits of
66 msgflg would not be granted; see Section 2.7, XSI Interprocess
67 Communication.
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69 EEXIST A message queue identifier exists for the argument key but
70 ((msgflg & IPC_CREAT) && (msgflg & IPC_EXCL)) is non-zero.
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72 ENOENT A message queue identifier does not exist for the argument key
73 and (msgflg & IPC_CREAT) is 0.
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75 ENOSPC A message queue identifier is to be created but the system-
76 imposed limit on the maximum number of allowed message queue
77 identifiers system-wide would be exceeded.
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79 The following sections are informative.
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82 None.
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85 The POSIX Realtime Extension defines alternative interfaces for inter‐
86 process communication (IPC). Application developers who need to use IPC
87 should design their applications so that modules using the IPC routines
88 described in Section 2.7, XSI Interprocess Communication can be easily
89 modified to use the alternative interfaces.
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92 None.
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95 None.
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98 Section 2.7, XSI Interprocess Communication, Section 2.8, Realtime,
99 ftok(), mq_close(), mq_getattr(), mq_notify(), mq_open(), mq_receive(),
100 mq_send(), mq_setattr(), mq_unlink(), msgctl(), msgrcv(), msgsnd()
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102 The Base Definitions volume of POSIX.1‐2008, Section 3.225, Message
103 Queue, <sys_msg.h>
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106 Portions of this text are reprinted and reproduced in electronic form
107 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
108 -- Portable Operating System Interface (POSIX), The Open Group Base
109 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
110 cal and Electronics Engineers, Inc and The Open Group. (This is
111 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
112 event of any discrepancy between this version and the original IEEE and
113 The Open Group Standard, the original IEEE and The Open Group Standard
114 is the referee document. The original Standard can be obtained online
115 at http://www.unix.org/online.html .
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117 Any typographical or formatting errors that appear in this page are
118 most likely to have been introduced during the conversion of the source
119 files to man page format. To report such errors, see https://www.ker‐
120 nel.org/doc/man-pages/reporting_bugs.html .
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124IEEE/The Open Group 2013 MSGGET(3P)