1MSGCTL(3P) POSIX Programmer's Manual MSGCTL(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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12 msgctl - XSI message control operations
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15 #include <sys/msg.h>
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17 int msgctl(int msqid, int cmd, struct msqid_ds *buf);
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21 The msgctl() function operates on XSI message queues (see the Base Def‐
22 initions volume of IEEE Std 1003.1-2001, Section 3.224, Message Queue).
23 It is unspecified whether this function interoperates with the realtime
24 interprocess communication facilities defined in Realtime .
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26 The msgctl() function shall provide message control operations as spec‐
27 ified by cmd. The following values for cmd, and the message control
28 operations they specify, are:
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30 IPC_STAT
31 Place the current value of each member of the msqid_ds data
32 structure associated with msqid into the structure pointed to by
33 buf. The contents of this structure are defined in <sys/msg.h>.
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35 IPC_SET
36 Set the value of the following members of the msqid_ds data
37 structure associated with msqid to the corresponding value found
38 in the structure pointed to by buf:
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41 msg_perm.uid
42 msg_perm.gid
43 msg_perm.mode
44 msg_qbytes
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46 IPC_SET can only be executed by a process with appropriate privileges
47 or that has an effective user ID equal to the value of msg_perm.cuid or
48 msg_perm.uid in the msqid_ds data structure associated with msqid. Only
49 a process with appropriate privileges can raise the value of
50 msg_qbytes.
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52 IPC_RMID
53 Remove the message queue identifier specified by msqid from the
54 system and destroy the message queue and msqid_ds data structure
55 associated with it. IPC_RMD can only be executed by a process
56 with appropriate privileges or one that has an effective user ID
57 equal to the value of msg_perm.cuid or msg_perm.uid in the
58 msqid_ds data structure associated with msqid.
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62 Upon successful completion, msgctl() shall return 0; otherwise, it
63 shall return -1 and set errno to indicate the error.
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66 The msgctl() function shall fail if:
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68 EACCES The argument cmd is IPC_STAT and the calling process does not
69 have read permission; see XSI Interprocess Communication .
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71 EINVAL The value of msqid is not a valid message queue identifier; or
72 the value of cmd is not a valid command.
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74 EPERM The argument cmd is IPC_RMID or IPC_SET and the effective user
75 ID of the calling process is not equal to that of a process with
76 appropriate privileges and it is not equal to the value of
77 msg_perm.cuid or msg_perm.uid in the data structure associated
78 with msqid.
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80 EPERM The argument cmd is IPC_SET, an attempt is being made to
81 increase to the value of msg_qbytes, and the effective user ID
82 of the calling process does not have appropriate privileges.
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85 The following sections are informative.
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88 None.
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91 The POSIX Realtime Extension defines alternative interfaces for inter‐
92 process communication (IPC). Application developers who need to use IPC
93 should design their applications so that modules using the IPC routines
94 described in XSI Interprocess Communication can be easily modified to
95 use the alternative interfaces.
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98 None.
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101 None.
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104 XSI Interprocess Communication, Realtime, mq_close(), mq_getattr(),
105 mq_notify(), mq_open(), mq_receive(), mq_send(), mq_setattr(),
106 mq_unlink(), msgget(), msgrcv(), msgsnd(), the Base Definitions volume
107 of IEEE Std 1003.1-2001, <sys/msg.h>
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110 Portions of this text are reprinted and reproduced in electronic form
111 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
112 -- Portable Operating System Interface (POSIX), The Open Group Base
113 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
114 Electrical and Electronics Engineers, Inc and The Open Group. In the
115 event of any discrepancy between this version and the original IEEE and
116 The Open Group Standard, the original IEEE and The Open Group Standard
117 is the referee document. The original Standard can be obtained online
118 at http://www.opengroup.org/unix/online.html .
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122IEEE/The Open Group 2003 MSGCTL(3P)