1.\" $NetBSD: listen.2,v 1.12 2002/02/08 01:28:18 ross 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 39.Sh NAME 40.Nm listen 41.Nd listen for connections on a socket 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.Fd #include \*[Lt]sys/socket.h\*[Gt] 46.Ft int 47.Fn listen "int s" "int backlog" 48.Sh DESCRIPTION 49To accept connections, a socket 50is first created with 51.Xr socket 2 , 52a willingness to accept incoming connections and 53a queue limit for incoming connections are specified with 54.Fn listen , 55and then the connections are 56accepted with 57.Xr accept 2 . 58The 59.Fn listen 60call applies only to sockets of type 61.Dv SOCK_STREAM 62or 63.Dv SOCK_SEQPACKET . 64.Pp 65The 66.Fa backlog 67parameter defines the maximum length the queue of 68pending connections may grow to. 69If a connection 70request arrives with the queue full the client may 71receive an error with an indication of 72.Er ECONNREFUSED , 73or, if the underlying protocol supports retransmission, 74the request may be ignored so that retries may succeed. 75.Sh RETURN VALUES 76A 0 return value indicates success; -1 indicates an error. 77.Sh ERRORS 78.Fn listen 79will fail if: 80.Bl -tag -width Er 81.It Bq Er EBADF 82The argument 83.Fa s 84is not a valid descriptor. 85.It Bq Er ENOTSOCK 86The argument 87.Fa s 88is not a socket. 89.It Bq Er EOPNOTSUPP 90The socket is not of a type that supports the operation 91.Fn listen . 92.El 93.Sh SEE ALSO 94.Xr accept 2 , 95.Xr connect 2 , 96.Xr socket 2 97.Sh HISTORY 98The 99.Fn listen 100function call appeared in 101.Bx 4.2 . 102.Sh BUGS 103The 104.Fa backlog 105is currently limited (silently) to 128. 106