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.
The msgctl() function operates on XSI message queues (see the Base
Definitions 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 Section2.8, Realtime.
The msgctl() function shall provide message control operations as
specified 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:
Also, the msg_ctime timestamp shall be set to the current
time, as described in Section 2.7.1, IPC GeneralDescription.
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
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.
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 InterprocessCommunication.
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.
The POSIX Realtime Extension defines alternative interfaces for
interprocess 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.
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 Electrical 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
IEEE/The Open Group 2013 MSGCTL(3P)