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.\" 32.\"/ 33.Dd March 4, 2018 34.Dt MSGGET 2 35.Os 36.Sh NAME 37.Nm msgget 38.Nd get message queue 39.Sh LIBRARY 40.Lb libc 41.Sh SYNOPSIS 42.In sys/msg.h 43.Ft int 44.Fn msgget "key_t key" "int msgflg" 45.Sh DESCRIPTION 46The 47.Fn msgget 48function 49returns the message queue identifier associated with 50.Fa key . 51A message queue identifier is a unique integer greater than zero. 52.Pp 53A message queue is created if either 54.Fa key 55is equal to 56.Dv IPC_PRIVATE , 57or 58.Fa key 59does not have a message queue identifier associated with it, and the 60.Dv IPC_CREAT 61bit is set in 62.Fa msgflg . 63.Pp 64If a new message queue is created, the data structure associated with it (the 65.Va msqid_ds 66structure, see 67.Xr msgctl 2 ) 68is initialized as follows: 69.Bl -bullet 70.It 71.Va msg_perm.cuid 72and 73.Va msg_perm.uid 74are set to the effective uid of the calling process. 75.It 76.Va msg_perm.gid 77and 78.Va msg_perm.cgid 79are set to the effective gid of the calling process. 80.It 81.Va msg_perm.mode 82is set to the lower 9 bits of 83.Fa msgflg 84which are set by ORing these constants: 85.Bl -tag -width 0000 86.It Dv 0400 87Read access for user. 88.It Dv 0200 89Write access for user. 90.It Dv 0040 91Read access for group. 92.It Dv 0020 93Write access for group. 94.It Dv 0004 95Read access for other. 96.It Dv 0002 97Write access for other. 98.El 99.It 100.Va msg_cbytes , 101.Va msg_qnum , 102.Va msg_lspid , 103.Va msg_lrpid , 104.Va msg_rtime , 105and 106.Va msg_stime 107are set to 0. 108.It 109.Va msg_qbytes 110is set to the system wide maximum value for the number of bytes in a queue 111.Pf ( Dv MSGMNB ) . 112.It 113.Va msg_ctime 114is set to the current time. 115.El 116.Sh RETURN VALUES 117Upon successful completion a positive message queue identifier is returned. 118Otherwise, -1 is returned and the global variable 119.Va errno 120is set to indicate the error. 121.Sh ERRORS 122.Bl -tag -width Er 123.It Bq Er EACCES 124A message queue is already associated with 125.Fa key 126and the caller has no permission to access it. 127.It Bq Er EEXIST 128Both 129.Dv IPC_CREAT 130and 131.Dv IPC_EXCL 132are set in 133.Fa msgflg , 134and a message queue is already associated with 135.Fa key . 136.It Bq Er ENOSPC 137A new message queue could not be created because the system limit for 138the number of message queues has been reached. 139.It Bq Er ENOENT 140.Dv IPC_CREAT 141was not set in 142.Fa msgflg 143and no message queue associated with 144.Fa key 145was found. 146.El 147.Sh SEE ALSO 148.Xr msgctl 2 , 149.Xr msgrcv 2 , 150.Xr msgsnd 2 151.Sh HISTORY 152Message queues appeared in the first release of 153.At V . 154