MSGCTL(3P) POSIX Programmer's Manual MSGCTL(3P)
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the correspond-
ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
msgctl - XSI message control operations
int msgctl(int msqid, int cmd, struct msqid_ds *buf);
The msgctl() function operates on XSI message queues (see the Base Definitions volume of IEEE Std 1003.1-2001, Section 3.224, Message
Queue). It is unspecified whether this function interoperates with the realtime interprocess communication facilities defined in 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:
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>.
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:
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
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.
Upon successful completion, msgctl() shall return 0; otherwise, it shall return -1 and set errno to indicate the error.
The msgctl() function shall fail if:
EACCES The argument cmd is IPC_STAT and the calling process does not have read permission; see XSI Interprocess Communication .
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
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 call-
ing 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 XSI Interprocess Communication can be easily modi-
fied to use the alternative interfaces.
XSI Interprocess Communication, 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 IEEE Std 1003.1-2001, <sys/msg.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html .
/The Open Group 2003 MSGCTL(3P)