215 lines
5.9 KiB
Groff
215 lines
5.9 KiB
Groff
.\" $NetBSD: msgctl.2,v 1.1 1995/10/16 23:49:15 jtc Exp $
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.\"
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.\" Copyright (c) 1995 Frank van der Linden
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed for the NetBSD Project
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.\" by Frank van der Linden
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.\" 4. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"/
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.Dd April 3, 2008
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.Dt MSGCTL 3
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.Os
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.Sh NAME
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.Nm msgctl
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.Nd message control operations
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/ipc.h
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.In sys/msg.h
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.Ft int
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.Fn msgctl "int msqid" "int cmd" "struct msqid_ds *buf"
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.Sh DESCRIPTION
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The
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.Fn msgctl
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system call performs some control operations on the message queue specified
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by
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.Fa msqid .
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.Pp
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Each message queue has a data structure associated with it, parts of which
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may be altered by
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.Fn msgctl
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and parts of which determine the actions of
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.Fn msgctl .
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The data structure is defined in
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.In sys/msg.h
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and contains (amongst others) the following members:
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.Bd -literal
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struct msqid_ds {
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struct ipc_perm msg_perm; /* msg queue permission bits */
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struct msg *msg_first; /* first message in the queue */
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struct msg *msg_last; /* last message in the queue */
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msglen_t msg_cbytes; /* number of bytes in use on the queue */
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msgqnum_t msg_qnum; /* number of msgs in the queue */
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msglen_t msg_qbytes; /* max # of bytes on the queue */
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pid_t msg_lspid; /* pid of last msgsnd() */
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pid_t msg_lrpid; /* pid of last msgrcv() */
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time_t msg_stime; /* time of last msgsnd() */
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long msg_pad1;
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time_t msg_rtime; /* time of last msgrcv() */
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long msg_pad2;
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time_t msg_ctime; /* time of last msgctl() */
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long msg_pad3;
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long msg_pad4[4];
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};
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.Ed
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.Pp
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The
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.Vt ipc_perm
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structure used inside the
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.Vt msqid_ds
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structure is defined in
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.In sys/ipc.h
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and looks like this:
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.Bd -literal
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struct ipc_perm {
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unsigned short cuid; /* creator user id */
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unsigned short cgid; /* creator group id */
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unsigned short uid; /* user id */
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unsigned short gid; /* group id */
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unsigned short mode; /* r/w permission */
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unsigned short seq; /* sequence # (to generate unique ipcid) */
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key_t key; /* user specified msg/sem/shm key */
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};
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.Ed
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.Pp
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The operation to be performed by
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.Fn msgctl
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is specified in
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.Fa cmd
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and is one of:
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.Bl -tag -width IPC_RMIDX
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.It Dv IPC_STAT
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Gather information about the message queue and place it in the
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structure pointed to by
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.Fa buf .
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.It Dv IPC_SET
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Set the value of the
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.Va msg_perm.uid ,
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.Va msg_perm.gid ,
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.Va msg_perm.mode
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and
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.Va msg_qbytes
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fields in the structure associated with
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.Fa msqid .
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The values are taken from the corresponding fields in the structure
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pointed to by
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.Fa buf .
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This operation can only be executed by the super-user, or a process that
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has an effective user id equal to either
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.Va msg_perm.cuid
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or
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.Va msg_perm.uid
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in the data structure associated with the message queue.
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The value of
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.Va msg_qbytes
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can only be increased by the super-user.
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Values for
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.Va msg_qbytes
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that exceed the system limit (MSGMNB from
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.In sys/msg.h )
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are silently truncated to that limit.
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.It Dv IPC_RMID
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Remove the message queue specified by
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.Fa msqid
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and destroy the data associated with it.
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Only the super-user or a process
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with an effective uid equal to the
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.Va msg_perm.cuid
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or
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.Va msg_perm.uid
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values in the data structure associated with the queue can do this.
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.El
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.Pp
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The permission to read from or write to a message queue (see
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.Xr msgsnd 3
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and
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.Xr msgrcv 3 )
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is determined by the
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.Va msg_perm.mode
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field in the same way as is
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done with files (see
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.Xr chmod 2 ) ,
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but the effective uid can match either the
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.Va msg_perm.cuid
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field or the
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.Va msg_perm.uid
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field, and the
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effective gid can match either
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.Va msg_perm.cgid
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or
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.Va msg_perm.gid .
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.Sh RETURN VALUES
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.Rv -std msgctl
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.Sh ERRORS
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The
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.Fn msgctl
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function
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EPERM
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The
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.Fa cmd
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argument
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is equal to IPC_SET or IPC_RMID and the caller is not the super-user, nor does
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the effective uid match either the
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.Va msg_perm.uid
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or
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.Va msg_perm.cuid
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fields of the data structure associated with the message queue.
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.Pp
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An attempt is made to increase the value of
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.Va msg_qbytes
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through IPC_SET
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but the caller is not the super-user.
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.It Bq Er EACCES
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The command is IPC_STAT
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and the caller has no read permission for this message queue.
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.It Bq Er EINVAL
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The
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.Fa msqid
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argument
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is not a valid message queue identifier.
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.Pp
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.Va cmd
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is not a valid command.
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.It Bq Er EFAULT
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The
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.Fa buf
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argument
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specifies an invalid address.
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.El
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.Sh SEE ALSO
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.Xr msgget 3 ,
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.Xr msgrcv 3 ,
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.Xr msgsnd 3
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.Sh HISTORY
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Message queues appeared in the first release of
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.At V .
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