1.\" $NetBSD: msgget.2,v 1.14 2004/05/13 10:20:58 wiz 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.Dd May 13, 2004 33.Dt MSGGET 2 34.Os 35.Sh NAME 36.Nm msgget 37.Nd get message queue identifier 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In sys/msg.h 42.Ft int 43.Fn msgget "key_t key" "int msgflg" 44.Sh DESCRIPTION 45The 46.Fn msgget 47system call returns the message queue identifier associated with 48.Fa key . 49A message queue identifier is a unique integer greater than zero. 50.Pp 51A message queue is created if either 52.Fa key 53is equal to 54.Dv IPC_PRIVATE , 55or 56.Fa key 57does not have a message queue identifier associated with it and the 58.Dv IPC_CREAT 59bit is set in 60.Fa msgflg . 61If both the 62.Dv IPC_CREAT 63bit and the 64.Dv IPC_EXCL 65bit are set in 66.Fa msgflg , 67and 68.Fa key 69has a message queue identifier associated with it already, 70the operation will fail. 71.Pp 72If a new message queue is created, the data structure associated with it (the 73.Va msqid_ds 74structure, see 75.Xr msgctl 2 ) 76is initialized as follows: 77.Bl -bullet 78.It 79.Va msg_perm.cuid 80and 81.Va msg_perm.uid 82are set to the effective uid of the calling process. 83.It 84.Va msg_perm.gid 85and 86.Va msg_perm.cgid 87are set to the effective gid of the calling process. 88.It 89.Va msg_perm.mode 90is set to the lower 9 bits of 91.Fa msgflg . 92.It 93.Va msg_qnum , 94.Va msg_lspid , 95.Va msg_lrpid , 96.Va msg_rtime , 97and 98.Va msg_stime 99are set to 0. 100.It 101.Va msg_qbytes 102is set to the system wide maximum value for the number of bytes in a queue 103.Pq Dv MSGMNB . 104.It 105.Va msg_ctime 106is set to the current time. 107.El 108.Sh RETURN VALUES 109Upon successful completion a positive message queue identifier is returned. 110Otherwise, \-1 is returned and the global variable 111.Va errno 112is set to indicate the error. 113.Sh ERRORS 114.Bl -tag -width Er 115.It Bq Er EACCES 116A message queue is already associated with 117.Fa key 118and the caller has no permission to access it. 119.It Bq Er EEXIST 120Both 121.Dv IPC_CREAT 122and 123.Dv IPC_EXCL 124are set in 125.Fa msgflg , 126and a message queue is already associated with 127.Fa key . 128.It Bq Er ENOSPC 129A new message queue could not be created because the system limit for 130the number of message queues has been reached. 131.It Bq Er ENOENT 132.Dv IPC_CREAT 133is not set in 134.Fa msgflg 135and no message queue associated with 136.Fa key 137was found. 138.El 139.Sh SEE ALSO 140.Xr msgctl 2 , 141.Xr msgrcv 2 , 142.Xr msgsnd 2 , 143.Xr ftok 3 144.Sh STANDARDS 145The 146.Nm 147system call conforms to 148.St -xsh5 . 149.Sh HISTORY 150Message queues appeared in the first release of 151.At V . 152