.\" Copyright 1993 Giorgio Ciucci (giorgio@crcc.it)
+.\" 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.\" manual page may be incorrect or out-of-date.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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+.\" %%%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
-.B msgctl
+.BR msgctl ()
performs the control operation specified by
.I cmd
on the message queue with identifier
.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() */
+ 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 (non-standard) */
- msgqnum_t msg_qnum; /* Current number of messages
+ 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
+ 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() */
-
+ 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
set to
.BR EIDRM ).
The calling process must have appropriate privileges
-or its effective user\-ID must be either that of the creator or owner
+or its effective user ID must be either that of the creator or owner
of the message queue.
-.SH "RETURN VALUE"
-On success, the return value will be 0
-otherwise \-1
-with
+.TP
+.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
+.I msginfo
+(thus, a cast is required),
+defined in
+.I <sys/msg.h>
+if the
+.B _GNU_SOURCE
+feature test macro is defined:
+.nf
+.in +4n
+
+struct msginfo {
+ 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; /* 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;
+ /* Maximum number of segments;
+ unused within kernel */
+};
+
+.in
+.fi
+The
+.IR msgmni ,
+.IR msgmax ,
+and
+.I msgmnb
+settings can be changed via
+.I /proc
+files of the same name; see
+.BR proc (5)
+for details.
+.TP
+.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
+about system resources consumed by message queues: the
+.I msgpool
+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
+on the system; and the
+.I msgtql
+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
+structure as for
+.BR IPC_STAT .
+However, the
+.I msqid
+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
+On success,
+.BR IPC_STAT ,
+.BR IPC_SET ,
+and
+.B IPC_RMID
+return 0.
+A successful
+.B IPC_INFO
+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
+operations to obtain information about all queues on the system.)
+A successful
+.B MSG_STAT
+operation returns the identifier of the queue whose index was given in
+.IR msqid .
+
+On error, \-1 is returned with
.I errno
indicating the error.
.SH ERRORS
On failure,
.I errno
is set to one of the following:
-.TP 11
+.TP
.B EACCES
The argument
.I cmd
.I cmd
or
.IR msqid .
+Or: for a
+.B MSG_STAT
+operation, the index value specified in
+.I msqid
+referred to an array slot that is currently unused.
.TP
.B EPERM
The argument
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
-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,
+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 ,
+.B MSG_STAT
+and
+.B MSG_INFO
+operations are used by the
+.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
+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, SVID. SVID does not document the EIDRM error condition.
-.SH "SEE ALSO"
+.SH SEE ALSO
.BR msgget (2),
.BR msgrcv (2),
.BR msgsnd (2),
-.BR ipc (5),
-.BR capabilities (7)
+.BR capabilities (7),
+.BR mq_overview (7),
+.BR svipc (7)
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