1.\" $NetBSD: listen.2,v 1.16 2004/05/13 10:20:58 wiz 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. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)listen.2 8.2 (Berkeley) 12/11/93 31.\" 32.Dd December 11, 1993 33.Dt LISTEN 2 34.Os 35.Sh NAME 36.Nm listen 37.Nd listen for connections on a socket 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In sys/socket.h 42.Ft int 43.Fn listen "int s" "int backlog" 44.Sh DESCRIPTION 45To accept connections, a socket 46is first created with 47.Xr socket 2 , 48a willingness to accept incoming connections and 49a queue limit for incoming connections are specified with 50.Fn listen , 51and then the connections are 52accepted with 53.Xr accept 2 . 54The 55.Fn listen 56call applies only to sockets of type 57.Dv SOCK_STREAM 58or 59.Dv SOCK_SEQPACKET . 60.Pp 61The 62.Fa backlog 63parameter defines the maximum length the queue of 64pending connections may grow to. 65If a connection 66request arrives with the queue full the client may 67receive an error with an indication of 68.Er ECONNREFUSED , 69or, if the underlying protocol supports retransmission, 70the request may be ignored so that retries may succeed. 71.Sh RETURN VALUES 72A 0 return value indicates success; \-1 indicates an error. 73.Sh ERRORS 74.Fn listen 75will fail if: 76.Bl -tag -width Er 77.It Bq Er EBADF 78The argument 79.Fa s 80is not a valid descriptor. 81.It Bq Er ENOTSOCK 82The argument 83.Fa s 84is not a socket. 85.It Bq Er EOPNOTSUPP 86The socket is not of a type that supports the operation 87.Fn listen . 88.El 89.Sh SEE ALSO 90.Xr accept 2 , 91.Xr connect 2 , 92.Xr socket 2 93.Sh HISTORY 94The 95.Fn listen 96function call appeared in 97.Bx 4.2 . 98.Sh BUGS 99The 100.Fa backlog 101is currently limited (silently) to 128. 102