.\" Copyright 1993 Giorgio Ciucci (giorgio@crcc.it)
-.\" and Copyright 2004, 2005 Michael Kerrisk <mtk-manpages@gmx.net>
+.\" and Copyright 2004, 2005 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
+.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
-.\"
+.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
-.\"
+.\"
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.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
.\"
.\" Modified Tue Oct 22 08:11:14 EDT 1996 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified Sun Feb 18 01:59:29 2001 by Andries E. Brouwer <aeb@cwi.nl>
-.\" Modified, 27 May 2004, Michael Kerrisk <mtk-manpages@gmx.net>
+.\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com>
.\" Added notes on CAP_IPC_OWNER requirement
-.\" Modified, 17 Jun 2004, Michael Kerrisk <mtk-manpages@gmx.net>
+.\" Modified, 17 Jun 2004, Michael Kerrisk <mtk.manpages@gmail.com>
.\" Added notes on CAP_SYS_ADMIN requirement for IPC_SET and IPC_RMID
-.\" Modified, 11 Nov 2004, Michael Kerrisk <mtk-manpages@gmx.net>
+.\" Modified, 11 Nov 2004, Michael Kerrisk <mtk.manpages@gmail.com>
.\" Language and formatting clean-ups
.\" Added msqid_ds and ipc_perm structure definitions
.\" 2005-08-02, mtk: Added IPC_INFO, MSG_INFO, MSG_STAT descriptions
.\"
-.TH MSGCTL 2 2004-11-10 "Linux 2.6.9" "Linux Programmer's Manual"
+.TH MSGCTL 2 2012-05-31 "Linux" "Linux Programmer's Manual"
.SH NAME
msgctl \- message control operations
.SH SYNOPSIS
.nf
-.B
-#include <sys/types.h>
-.B
-#include <sys/ipc.h>
-.B
-#include <sys/msg.h>
+.B #include <sys/types.h>
+.B #include <sys/ipc.h>
+.B #include <sys/msg.h>
+
+.BI "int msgctl(int " msqid ", int " cmd ", struct msqid_ds *" buf );
.fi
-.sp
-.BI "int msgctl(int " msqid ,
-.BI "int " cmd ,
-.BI "struct msqid_ds *" buf );
.SH DESCRIPTION
.BR msgctl ()
performs the control operation specified by
.PP
The
.I msqid_ds
-data structure is defined in <sys/msg.h> as follows:
+data structure is defined in \fI<sys/msg.h>\fP as follows:
.nf
.in +4n
struct msqid_ds {
- struct ipc_perm msg_perm; /* Ownership and permissions */
- time_t msg_stime; /* Time of last msgsnd() */
- time_t msg_rtime; /* Time of last msgrcv() */
- time_t msg_ctime; /* Time of last change */
- unsigned long __msg_cbytes; /* Current number of bytes in
- queue (non-standard) */
- msgqnum_t msg_qnum; /* Current number of messages
- in queue */
- msglen_t msg_qbytes; /* Maximum number of bytes
- allowed in queue */
- pid_t msg_lspid; /* PID of last msgsnd() */
- pid_t msg_lrpid; /* PID of last msgrcv() */
+ struct ipc_perm msg_perm; /* Ownership and permissions */
+ time_t msg_stime; /* Time of last msgsnd(2) */
+ time_t msg_rtime; /* Time of last msgrcv(2) */
+ time_t msg_ctime; /* Time of last change */
+ unsigned long __msg_cbytes; /* Current number of bytes in
+ queue (nonstandard) */
+ msgqnum_t msg_qnum; /* Current number of messages
+ in queue */
+ msglen_t msg_qbytes; /* Maximum number of bytes
+ allowed in queue */
+ pid_t msg_lspid; /* PID of last msgsnd(2) */
+ pid_t msg_lrpid; /* PID of last msgrcv(2) */
};
-.in -4n
+.in
.fi
.PP
The
.I ipc_perm
-structure is defined in <sys/ipc.h> as follows
+structure is defined as follows
(the highlighted fields are settable using
.BR IPC_SET ):
.PP
.nf
.in +4n
struct ipc_perm {
- key_t key; /* Key supplied to msgget() */
- uid_t \fBuid\fP; /* Effective UID of owner */
- gid_t \fBgid\fP; /* Effective GID of owner */
- uid_t cuid; /* Effective UID of creator */
- gid_t cgid; /* Effective GID of creator */
- unsigned short \fBmode\fP; /* Permissions */
- unsigned short seq; /* Sequence number */
+ key_t __key; /* Key supplied to msgget(2) */
+ uid_t \fBuid\fP; /* Effective UID of owner */
+ gid_t \fBgid\fP; /* Effective GID of owner */
+ uid_t cuid; /* Effective UID of creator */
+ gid_t cgid; /* Effective GID of creator */
+ unsigned short \fBmode\fP; /* Permissions */
+ unsigned short __seq; /* Sequence number */
};
-.in -4n
+.in
.fi
.PP
Valid values for
updating also its
.I msg_ctime
member.
-The following members of the structure are updated:
+The following members of the structure are updated:
.IR msg_qbytes ,
.IR msg_perm.uid ,
.IR msg_perm.gid ,
.IR msg_perm.mode .
The effective UID of the calling process must match the owner
.RI ( msg_perm.uid )
-or creator
+or creator
.RI ( msg_perm.cuid )
of the message queue, or the caller must be privileged.
Appropriate privilege (Linux: the
or its effective user ID must be either that of the creator or owner
of the message queue.
.TP
-.BR IPC_INFO " (Linux specific)"
-Returns information about system-wide message queue limits and
+.BR IPC_INFO " (Linux-specific)"
+Returns information about system-wide message queue limits and
parameters in the structure pointed to by
.IR buf .
This structure is of type
-.IR msginfo
+.I msginfo
(thus, a cast is required),
defined in
.I <sys/msg.h>
-if the _GNU_SOURCE feature test macro is defined:
+if the
+.B _GNU_SOURCE
+feature test macro is defined:
.nf
-.in +2n
+.in +4n
struct msginfo {
- int msgpool; /* Size in bytes of buffer pool used
- to hold message data; unused */
- int msgmap; /* Max. # of entries in message
- map; unused */
- int msgmax; /* Max. # of bytes that can be
+ int msgpool; /* Size in kibibytes of buffer pool
+ used to hold message data;
+ unused within kernel */
+ int msgmap; /* Maximum number of entries in message
+ map; unused within kernel */
+ int msgmax; /* Maximum number of bytes that can be
written in a single message */
- int msgmnb; /* Max. # of bytes that can be written to
- queue; used to initialize msg_qbytes
- during queue creation (msgget()) */
- int msgmni; /* Max. # of message queues */
- int msgssz; /* Message segment size; unused */
- int msgtql; /* Max. # of messages on all queues
- in system; unused */
+ int msgmnb; /* Maximum number of bytes that can be
+ written to queue; used to initialize
+ msg_qbytes during queue creation
+ (msgget(2)) */
+ int msgmni; /* Maximum number of message queues */
+ int msgssz; /* Message segment size;
+ unused within kernel */
+ int msgtql; /* Maximum number of messages on all queues
+ in system; unused within kernel */
unsigned short int msgseg;
- /* Max. # of segments; unused */
+ /* Maximum number of segments;
+ unused within kernel */
};
-.in -2n
+.in
.fi
-The
+The
.IR msgmni ,
.IR msgmax ,
and
.I msgmnb
settings can be changed via
-.I /proc
+.I /proc
files of the same name; see
-.BR proc (5)
+.BR proc (5)
for details.
.TP
-.BR MSG_INFO " (Linux specific)"
+.BR MSG_INFO " (Linux-specific)"
Returns a
.I msginfo
structure containing the same information as for
.BR IPC_INFO ,
-except that the following fields are returned with information
+except that the following fields are returned with information
about system resources consumed by message queues: the
.I msgpool
-field returns the number of message queues that currently exist
+field returns the number of message queues that currently exist
on the system; the
.I msgmap
-field returns the total number of messages in all queues
+field returns the total number of messages in all queues
on the system; and the
.I msgtql
-field returns the total number of bytes in all messages
+field returns the total number of bytes in all messages
in all queues on the system.
.TP
-.BR MSG_STAT " (Linux specific)"
-Returns a
-.I msqid_ds
+.BR MSG_STAT " (Linux-specific)"
+Returns a
+.I msqid_ds
structure as for
.BR IPC_STAT .
However, the
argument is not a queue identifier, but instead an index into
the kernel's internal array that maintains information about
all message queues on the system.
-.SH "RETURN VALUE"
+.SH RETURN VALUE
On success,
.BR IPC_STAT ,
.BR IPC_SET ,
and
-.BR IPC_RMID
+.B IPC_RMID
return 0.
A successful
.B IPC_INFO
-or
+or
.B MSG_INFO
operation returns the index of the highest used entry in the
kernel's internal array recording information about all
message queues.
(This information can be used with repeated
-.B MSG_STAT
+.B MSG_STAT
operations to obtain information about all queues on the system.)
A successful
.B MSG_STAT
On failure,
.I errno
is set to one of the following:
-.TP 11
+.TP
.B EACCES
The argument
.I cmd
is equal to
-.BR IPC_STAT
+.B IPC_STAT
or
.BR MSG_STAT ,
but the calling process does not have read permission on the message queue
.IR msqid .
Or: for a
.B MSG_STAT
-operation, the index value specified in
+operation, the index value specified in
.I msqid
referred to an array slot that is currently unused.
.TP
and the process is not privileged (Linux: it does not have the
.B CAP_SYS_ADMIN
capability).
+.SH CONFORMING TO
+SVr4, POSIX.1-2001.
+.\" SVID does not document the EIDRM error condition.
.SH NOTES
+The inclusion of
+.I <sys/types.h>
+and
+.I <sys/ipc.h>
+isn't required on Linux or by any version of POSIX.
+However,
+some old implementations required the inclusion of these header files,
+and the SVID also documented their inclusion.
+Applications intended to be portable to such old systems may need
+to include these header files.
+.\" Like Linux, the FreeBSD man pages still document
+.\" the inclusion of these header files.
+
The
.BR IPC_INFO ,
-.BR MSG_STAT
+.B MSG_STAT
and
.B MSG_INFO
operations are used by the
-.BR ipcs (8)
+.BR ipcs (1)
program to provide information on allocated resources.
In the future these may modified or moved to a /proc file system
interface.
-Various fields in the \fIstruct msqid_ds\fP were shorts under Linux 2.2
-and have become longs under Linux 2.4. To take advantage of this,
+Various fields in the \fIstruct msqid_ds\fP were
+typed as
+.I short
+under Linux 2.2
+and have become
+.I long
+under Linux 2.4.
+To take advantage of this,
a recompilation under glibc-2.1.91 or later should suffice.
-(The kernel distinguishes old and new calls by an IPC_64 flag in
+(The kernel distinguishes old and new calls by an
+.B IPC_64
+flag in
.IR cmd .)
-.SH "CONFORMING TO"
-SVr4, POSIX.1-2001.
-.\" SVID does not document the EIDRM error condition.
-.SH "SEE ALSO"
+.SH SEE ALSO
.BR msgget (2),
.BR msgrcv (2),
.BR msgsnd (2),
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