1.\" $NetBSD: listen.2,v 1.7 1996/02/16 20:38:45 phil Exp $ 2.\" 3.\" Copyright (c) 1983, 1991, 1993 4.\" The Regents of the University of California. 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 by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)listen.2 8.2 (Berkeley) 12/11/93 35.\" 36.Dd December 11, 1993 37.Dt LISTEN 2 38.Os BSD 4.2 39.Sh NAME 40.Nm listen 41.Nd listen for connections on a socket 42.Sh SYNOPSIS 43.Fd #include <sys/socket.h> 44.Ft int 45.Fn listen "int s" "int backlog" 46.Sh DESCRIPTION 47To accept connections, a socket 48is first created with 49.Xr socket 2 , 50a willingness to accept incoming connections and 51a queue limit for incoming connections are specified with 52.Fn listen , 53and then the connections are 54accepted with 55.Xr accept 2 . 56The 57.Fn listen 58call applies only to sockets of type 59.Dv SOCK_STREAM 60or 61.Dv SOCK_SEQPACKET. 62.Pp 63The 64.Fa backlog 65parameter defines the maximum length the queue of 66pending connections may grow to. 67If a connection 68request arrives with the queue full the client may 69receive an error with an indication of 70.Er ECONNREFUSED , 71or, if the underlying protocol supports retransmission, 72the request may be ignored so that retries may succeed. 73.Sh RETURN VALUES 74A 0 return value indicates success; -1 indicates an error. 75.Sh ERRORS 76.Fn Listen 77will fail if: 78.Bl -tag -width Er 79.It Bq Er EBADF 80The argument 81.Fa s 82is not a valid descriptor. 83.It Bq Er ENOTSOCK 84The argument 85.Fa s 86is not a socket. 87.It Bq Er EOPNOTSUPP 88The socket is not of a type that supports the operation 89.Fn listen . 90.El 91.Sh SEE ALSO 92.Xr accept 2 , 93.Xr connect 2 , 94.Xr socket 2 95.Sh BUGS 96The 97.Fa backlog 98is currently limited (silently) to 128. 99.Sh HISTORY 100The 101.Fn listen 102function call appeared in 103.Bx 4.2 . 104