1MSGCTL(3P) POSIX Programmer's Manual MSGCTL(3P)
2
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
12 msgctl — XSI message control operations
13
15 #include <sys/msg.h>
16 int msgctl(int msqid, int cmd, struct msqid_ds *buf);
18
20 The msgctl() 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.
24 The msgctl() function shall provide message control operations as spec‐
26 ified by cmd. The following values for cmd, and the message control
27 operations they specify, are:
28 IPC_STAT Place the current value of each member of the msqid_ds data
30 structure associated with msqid into the structure pointed
31 to by buf. The contents of this structure are defined in
32 <sys/msg.h>.
33 IPC_SET Set the value of the following members of the msqid_ds data
35 structure associated with msqid to the corresponding value
36 found in the structure pointed to by buf:
37 msg_perm.uid
40 msg_perm.gid
41 msg_perm.mode
42 msg_qbytes
43 Also, the msg_ctime timestamp shall be set to the current
45 time, as described in Section 2.7.1, IPC General Descrip‐
46 tion.
47 IPC_SET can only be executed by a process with appropriate
49 privileges or that has an effective user ID equal to the
50 value of msg_perm.cuid or msg_perm.uid in the msqid_ds data
51 structure associated with msqid. Only a process with
52 appropriate privileges can raise the value of msg_qbytes.
53 IPC_RMID Remove the message queue identifier specified by msqid from
55 the system and destroy the message queue and msqid_ds data
56 structure associated with it. IPC_RMD can only be executed
57 by a process with appropriate privileges or one that has an
58 effective user ID equal to the value of msg_perm.cuid or
59 msg_perm.uid in the msqid_ds data structure associated with
60 msqid.
61
63 Upon successful completion, msgctl() shall return 0; otherwise, it
64 shall return -1 and set errno to indicate the error.
65
67 The msgctl() function shall fail if:
68 EACCES The argument cmd is IPC_STAT and the calling process does not
70 have read permission; see Section 2.7, XSI Interprocess Communi‐
71 cation.
72 EINVAL The value of msqid is not a valid message queue identifier; or
74 the value of cmd is not a valid command.
75 EPERM The argument cmd is IPC_RMID or IPC_SET and the effective user
77 ID of the calling process is not equal to that of a process with
78 appropriate privileges and it is not equal to the value of
79 msg_perm.cuid or msg_perm.uid in the data structure associated
80 with msqid.
81 EPERM The argument cmd is IPC_SET, an attempt is being made to
83 increase to the value of msg_qbytes, and the effective user ID
84 of the calling process does not have appropriate privileges.
85 The following sections are informative.
87
89 None.
90
92 The POSIX Realtime Extension defines alternative interfaces for inter‐
93 process communication (IPC). Application developers who need to use IPC
94 should design their applications so that modules using the IPC routines
95 described in Section 2.7, XSI Interprocess Communication can be easily
96 modified to use the alternative interfaces.
97
99 None.
100
102 None.
103
105 Section 2.7, XSI Interprocess Communication, Section 2.8, Realtime,
106 mq_close(), mq_getattr(), mq_notify(), mq_open(), mq_receive(),
107 mq_send(), mq_setattr(), mq_unlink(), msgget(), msgrcv(), msgsnd()
108 The Base Definitions volume of POSIX.1‐2017, Section 3.226, Message
110 Queue, <sys_msg.h>
111
113 Portions of this text are reprinted and reproduced in electronic form
114 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
115 table Operating System Interface (POSIX), The Open Group Base Specifi‐
116 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
117 Electrical and Electronics Engineers, Inc and The Open Group. In the
118 event of any discrepancy between this version and the original IEEE and
119 The Open Group Standard, the original IEEE and The Open Group Standard
120 is the referee document. The original Standard can be obtained online
121 at http://www.opengroup.org/unix/online.html .
122 Any typographical or formatting errors that appear in this page are
124 most likely to have been introduced during the conversion of the source
125 files to man page format. To report such errors, see https://www.ker‐
126 nel.org/doc/man-pages/reporting_bugs.html .
127IEEE/The Open Group 2017 MSGCTL(3P)