.\"	$NetBSD: msgget.2,v 1.1 1995/10/16 23:49:19 jtc Exp $
.\"
.\" Copyright (c) 1995 Frank van der Linden
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.\"      by Frank van der Linden
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.\" $FreeBSD: head/lib/libc/sys/msgget.2 195656 2009-07-13 12:53:43Z trasz $
.\"
.\"/
.Dd July 9, 2009
.Dt MSGGET 2
.Os
.Sh NAME
.Nm msgget
.Nd get message queue
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/types.h
.In sys/ipc.h
.In sys/msg.h
.Ft int
.Fn msgget "key_t key" "int msgflg"
.Sh DESCRIPTION
The
.Fn msgget
function
returns the message queue identifier associated with
.Fa key .
A message queue identifier is a unique integer greater than zero.
.Pp
A message queue is created if either
.Fa key
is equal to
.Dv IPC_PRIVATE ,
or
.Fa key
does not have a message queue identifier associated with it, and the
.Dv IPC_CREAT
bit is set in
.Fa msgflg .
.Pp
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
.Pf ( Dv 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 EACCES
A message queue is already associated with
.Fa key
and the caller has no permission to access it.
.It Bq Er EEXIST
Both
.Dv IPC_CREAT
and
.Dv 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
.Dv 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 V .