1.\" $NetBSD: msgget.2,v 1.1 1995/10/16 23:49:19 jtc Exp $ 2.\" 3.\" Copyright (c) 1995 Frank van der Linden 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed for the NetBSD Project 17.\" by Frank van der Linden 18.\" 4. The name of the author may not be used to endorse or promote products 19.\" derived from this software without specific prior written permission 20.\" 21.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 22.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 23.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 24.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 25.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 26.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 27.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 28.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 29.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 30.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 31.\" $FreeBSD$ 32.\" 33.\"/ 34.Dd March 4, 2018 35.Dt MSGGET 2 36.Os 37.Sh NAME 38.Nm msgget 39.Nd get message queue 40.Sh LIBRARY 41.Lb libc 42.Sh SYNOPSIS 43.In sys/msg.h 44.Ft int 45.Fn msgget "key_t key" "int msgflg" 46.Sh DESCRIPTION 47The 48.Fn msgget 49function 50returns the message queue identifier associated with 51.Fa key . 52A message queue identifier is a unique integer greater than zero. 53.Pp 54A message queue is created if either 55.Fa key 56is equal to 57.Dv IPC_PRIVATE , 58or 59.Fa key 60does not have a message queue identifier associated with it, and the 61.Dv IPC_CREAT 62bit is set in 63.Fa msgflg . 64.Pp 65If a new message queue is created, the data structure associated with it (the 66.Va msqid_ds 67structure, see 68.Xr msgctl 2 ) 69is initialized as follows: 70.Bl -bullet 71.It 72.Va msg_perm.cuid 73and 74.Va msg_perm.uid 75are set to the effective uid of the calling process. 76.It 77.Va msg_perm.gid 78and 79.Va msg_perm.cgid 80are set to the effective gid of the calling process. 81.It 82.Va msg_perm.mode 83is set to the lower 9 bits of 84.Fa msgflg 85which are set by ORing these constants: 86.Bl -tag -width 0000 87.It Dv 0400 88Read access for user. 89.It Dv 0200 90Write access for user. 91.It Dv 0040 92Read access for group. 93.It Dv 0020 94Write access for group. 95.It Dv 0004 96Read access for other. 97.It Dv 0002 98Write access for other. 99.El 100.It 101.Va msg_cbytes , 102.Va msg_qnum , 103.Va msg_lspid , 104.Va msg_lrpid , 105.Va msg_rtime , 106and 107.Va msg_stime 108are set to 0. 109.It 110.Va msg_qbytes 111is set to the system wide maximum value for the number of bytes in a queue 112.Pf ( Dv MSGMNB ) . 113.It 114.Va msg_ctime 115is set to the current time. 116.El 117.Sh RETURN VALUES 118Upon successful completion a positive message queue identifier is returned. 119Otherwise, -1 is returned and the global variable 120.Va errno 121is set to indicate the error. 122.Sh ERRORS 123.Bl -tag -width Er 124.It Bq Er EACCES 125A message queue is already associated with 126.Fa key 127and the caller has no permission to access it. 128.It Bq Er EEXIST 129Both 130.Dv IPC_CREAT 131and 132.Dv IPC_EXCL 133are set in 134.Fa msgflg , 135and a message queue is already associated with 136.Fa key . 137.It Bq Er ENOSPC 138A new message queue could not be created because the system limit for 139the number of message queues has been reached. 140.It Bq Er ENOENT 141.Dv IPC_CREAT 142was not set in 143.Fa msgflg 144and no message queue associated with 145.Fa key 146was found. 147.El 148.Sh SEE ALSO 149.Xr msgctl 2 , 150.Xr msgrcv 2 , 151.Xr msgsnd 2 152.Sh HISTORY 153Message queues appeared in the first release of 154.At V . 155