MSGCTL(3P) POSIX Programmer's Manual MSGCTL(3P)PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
Linux manual page for details of Linux behavior), or the interface may
not be implemented on Linux.
NAMEmsgctl — XSI message control operations
SYNOPSIS
#include <sys/msg.h>
int msgctl(int msqid, int cmd, struct msqid_ds *buf);
DESCRIPTION
The msgctl() function operates on XSI message queues (see the Base Def‐
initions volume of POSIX.1‐2008, Section 3.225, Message Queue). It is
unspecified whether this function interoperates with the realtime
interprocess communication facilities defined in Section 2.8, Realtime.
The msgctl() function shall provide message control operations as spec‐
ified by cmd. The following values for cmd, and the message control
operations they specify, are:
IPC_STAT Place the current value of each member of the msqid_ds data
structure associated with msqid into the structure pointed
to by buf. The contents of this structure are defined in
<sys/msg.h>.
IPC_SET Set the value of the following members of the msqid_ds data
structure associated with msqid to the corresponding value
found in the structure pointed to by buf:
msg_perm.uid
msg_perm.gid
msg_perm.mode
msg_qbytes
Also, the msg_ctime timestamp shall be set to the current
time, as described in Section 2.7.1, IPC General Descrip‐
tion.
IPC_SET can only be executed by a process with appropriate
privileges or that has an effective user ID equal to the
value of msg_perm.cuid or msg_perm.uid in the msqid_ds data
structure associated with msqid. Only a process with
appropriate privileges can raise the value of msg_qbytes.
IPC_RMID Remove the message queue identifier specified by msqid from
the system and destroy the message queue and msqid_ds data
structure associated with it. IPC_RMD can only be executed
by a process with appropriate privileges or one that has an
effective user ID equal to the value of msg_perm.cuid or
msg_perm.uid in the msqid_ds data structure associated with
msqid.
RETURN VALUE
Upon successful completion, msgctl() shall return 0; otherwise, it
shall return −1 and set errno to indicate the error.
ERRORS
The msgctl() function shall fail if:
EACCES The argument cmd is IPC_STAT and the calling process does not
have read permission; see Section 2.7, XSI Interprocess Communi‐
cation.
EINVAL The value of msqid is not a valid message queue identifier; or
the value of cmd is not a valid command.
EPERM The argument cmd is IPC_RMID or IPC_SET and the effective user
ID of the calling process is not equal to that of a process with
appropriate privileges and it is not equal to the value of
msg_perm.cuid or msg_perm.uid in the data structure associated
with msqid.
EPERM The argument cmd is IPC_SET, an attempt is being made to
increase to the value of msg_qbytes, and the effective user ID
of the calling process does not have appropriate privileges.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The POSIX Realtime Extension defines alternative interfaces for inter‐
process communication (IPC). Application developers who need to use IPC
should design their applications so that modules using the IPC routines
described in Section 2.7, XSI Interprocess Communication can be easily
modified to use the alternative interfaces.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
Section 2.7, XSI Interprocess Communication, Section 2.8, Realtime,
mq_close(), mq_getattr(), mq_notify(), mq_open(), mq_receive(),
mq_send(), mq_setattr(), mq_unlink(), msgget(), msgrcv(), msgsnd()
The Base Definitions volume of POSIX.1‐2008, Section 3.225, Message
Queue, <sys_msg.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker‐
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IEEE/The Open Group 2013 MSGCTL(3P)
