.\"	$OpenBSD: msgget.2,v 1.3 1998/07/06 18:28:01 deraadt Exp $	
.\"	$NetBSD: msgget.2,v 1.1 1995/10/16 23:49:19 jtc Exp $	
.\"
.\" Copyright (c) 1995 Frank van der Linden
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
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.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
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.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"      This product includes software developed for the NetBSD Project
.\"      by Frank van der Linden
.\" 4. The name of the author may not be used to endorse or promote products
.\"    derived from this software without specific prior written permission
.\"
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.\"/
.Dd August 17, 1995
.Dt MSGGET 2
.Os
.Sh NAME
.Nm msgget
.Nd get message queue
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/ipc.h>
.Fd #include <sys/msg.h>
.Ft int
.Fn msgget "key_t key" "int msgflg"
.Sh DESCRIPTION
.Fn msgget
returns the message queue identifier associated with
.Fa key .
A message queue identifier is a unique integer greater than zero.

A message queue is created if either
.Fa key
is equal to IPC_PRIVATE, or
.Fa key
does not have a message queue identifier associated with it, and the IPC_CREAT
bit is set in
.Fa msgflg.

If a new message queue is created, the data structure associated with it (the
.Va msqid_ds
structure, see
.Xr msgctl 2 )
is initialized as follows:
.Bl -bullet
.It 
.Va msg_perm.cuid
and
.Va msg_perm.uid
are set to the effective uid of the calling process.
.It
.Va msg_perm.gid
and
.Va msg_perm.cgid
are set to the effective gid of the calling process.
.It
.Va msg_perm.mode
is set to the lower 9 bits of
.Fa msgflg .
.It
.Va msg_cbytes ,
.Va msg_qnum ,
.Va msg_lspid ,
.Va msg_lrpid ,
.Va msg_rtime ,
and 
.Va msg_stime
are set to 0
.It
.Va msg_qbytes
is set to the system wide maximum value for the number of bytes in a queue
(MSGMNB).
.It
.Va msg_ctime
is set to the current time.
.El
.Sh RETURN VALUES
Upon successful completion a positive message queue identifier is returned.
Otherwise, -1 is returned and the global variable
.Va errno
is set to indicate the error.
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EACESS
A message queue is already associated with
.Fa key
and the caller has no permission to access it.
.It Bq Er EEXIST
Both IPC_CREAT and IPC_EXCL are set in
.Fa msgflg ,
and a message queue is already associated with
.Fa key .
.It Bq Er ENOSPC
A new message queue could not be created because the system limit for
the number of message queues has been reached.
.It Bq Er ENOENT
IPC_CREAT was not set in
.Fa msgflg
and no message queue associated with
.Fa key
was found.
.El
.Sh SEE ALSO
.Xr msgctl 2 ,
.Xr msgrcv 2 ,
.Xr msgsnd 2
.Sh HISTORY
Message queues appeared in the first release of AT&T Unix System V.