1.\" $OpenBSD: msgsnd.2,v 1.21 2019/07/18 13:45:03 schwarze Exp $ 2.\" $NetBSD: msgsnd.2,v 1.2 1997/03/27 08:20:36 mikel Exp $ 3.\" 4.\" Copyright (c) 1995 Frank van der Linden 5.\" All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. All advertising materials mentioning features or use of this software 16.\" must display the following acknowledgement: 17.\" This product includes software developed for the NetBSD Project 18.\" by Frank van der Linden 19.\" 4. The name of the author may not be used to endorse or promote products 20.\" derived from this software without specific prior written permission 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 23.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 24.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 25.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 26.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 27.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 28.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 29.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 30.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 31.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 32.\"/ 33.Dd $Mdocdate: July 18 2019 $ 34.Dt MSGSND 2 35.Os 36.Sh NAME 37.Nm msgsnd 38.Nd send a message to a message queue 39.Sh SYNOPSIS 40.In sys/msg.h 41.Ft int 42.Fn msgsnd "int msqid" "const void *msgp" "size_t msgsz" "int msgflg" 43.Sh DESCRIPTION 44The 45.Fn msgsnd 46function sends a message to the message queue specified by 47.Fa msqid . 48.Fa msgp 49points to a structure containing the message. 50This structure should consist of the following members: 51.Bd -literal -offset indent 52long mtype; /* message type */ 53char mtext[1]; /* body of message */ 54.Ed 55.Pp 56.Fa mtype 57is an integer greater than 0 that can be used for selecting messages (see 58.Xr msgrcv 2 ) ; 59.Fa mtext 60is an array of 61.Fa msgsz 62bytes, with a size between 0 and that of the system limit 63.Pq Dv MSGMAX . 64.Pp 65If the number of bytes already on the message queue plus 66.Fa msgsz 67is bigger than the maximum number of bytes on the message queue 68.Po Fa msg_qbytes , 69 see 70.Xr msgctl 2 71.Pc , 72or the number of messages on all queues system-wide is already equal to 73the system limit, 74.Fa msgflg 75determines the action of 76.Fn msgsnd . 77If 78.Fa msgflg 79has 80.Dv IPC_NOWAIT 81mask set in it, the call will return immediately. 82If 83.Fa msgflg 84does not have 85.Dv IPC_NOWAIT 86set in it, the call will block until: 87.Bl -bullet 88.It 89The condition which caused the call to block does no longer exist. 90The message will be sent. 91.It 92The message queue is removed, in which case \-1 will be returned, and 93.Va errno 94is set to 95.Er EIDRM . 96.It 97The caller catches a signal. 98The call returns with 99.Va errno 100set to 101.Er EINTR . 102.El 103.Pp 104After a successful call, the data structure associated with the message 105queue is updated in the following way: 106.Bl -bullet 107.It 108.Fa msg_cbytes 109is incremented by the size of the message. 110.It 111.Fa msg_qnum 112is incremented by 1. 113.It 114.Fa msg_lspid 115is set to the pid of the calling process. 116.It 117.Fa msg_stime 118is set to the current time. 119.El 120.Sh RETURN VALUES 121.Rv -std 122.Sh ERRORS 123.Fn msgsnd 124will fail if: 125.Bl -tag -width Er 126.It Bq Er EINVAL 127.Fa msqid 128is not a valid message queue identifier. 129.Pp 130.Fa mtype 131is less than 1. 132.Pp 133.Fa msgsz 134is greater than 135.Fa msg_qbytes . 136.It Bq Er EACCES 137The calling process does not have write access to the message queue. 138.It Bq Er EAGAIN 139There was no space for this message either on the queue, or in the whole 140system, and 141.Dv IPC_NOWAIT 142was set in 143.Fa msgflg . 144.It Bq Er EFAULT 145.Fa msgp 146points to an invalid address. 147.It Bq Er EINTR 148The system call was interrupted by the delivery of a signal. 149.It Bq Er EIDRM 150The message queue was removed while 151.Fn msgsnd 152was waiting for a resource to become available in order to deliver the 153message. 154.El 155.Sh SEE ALSO 156.Xr msgctl 2 , 157.Xr msgget 2 , 158.Xr msgrcv 2 159.Sh STANDARDS 160The 161.Fn msgsnd 162function conforms to the X/Open System Interfaces option of 163.St -p1003.1-2008 . 164.Sh HISTORY 165Message queues first appeared in 166.At V.1 167and have been available since 168.Nx 1.0 . 169