1.\" $OpenBSD: listen.2,v 1.2 1996/03/19 23:15:16 niklas Exp $ 2.\" $NetBSD: listen.2,v 1.7 1996/02/16 20:38:45 phil Exp $ 3.\" 4.\" Copyright (c) 1983, 1991, 1993 5.\" The Regents of the University of California. 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 by the University of 18.\" California, Berkeley and its contributors. 19.\" 4. Neither the name of the University nor the names of its contributors 20.\" may be used to endorse or promote products derived from this software 21.\" without specific prior written permission. 22.\" 23.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 24.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 26.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 27.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33.\" SUCH DAMAGE. 34.\" 35.\" @(#)listen.2 8.2 (Berkeley) 12/11/93 36.\" 37.Dd March 18, 2015 38.Dt LISTEN 2 39.Os BSD 4.2 40.Sh NAME 41.Nm listen 42.Nd listen for connections on a socket 43.Sh SYNOPSIS 44.Fd #include <sys/socket.h> 45.Ft int 46.Fo listen 47.Fa "int socket" 48.Fa "int backlog" 49.Fc 50.Sh DESCRIPTION 51Creation of socket-based connections requires several operations. 52First, a socket is created with 53.Xr socket 2 . 54Next, a willingness to accept incoming connections and 55a queue limit for incoming connections are specified with 56.Fn listen . 57Finally, the connections are 58accepted with 59.Xr accept 2 . 60The 61.Fn listen 62call applies only to sockets of type 63.Dv SOCK_STREAM. 64.\"or 65.\".Dv SOCK_SEQPACKET. 66.Pp 67The 68.Fa backlog 69parameter defines the maximum length 70for the queue of pending connections. 71If a connection 72request arrives with the queue full, 73the client may receive an error with an indication of 74.Er ECONNREFUSED . 75Alternatively, if the underlying protocol supports retransmission, 76the request may be ignored so that retries may succeed. 77.Sh RETURN VALUES 78.Rv -std listen 79.Sh ERRORS 80.Fn listen 81will fail if: 82.Bl -tag -width Er 83.\" ========== 84.It Bq Er EACCES 85The current process has insufficient privileges. 86.\" ========== 87.It Bq Er EBADF 88The argument 89.Fa socket 90is not a valid file descriptor. 91.\" ========== 92.It Bq Er EDESTADDRREQ 93The socket is not bound to a local address 94and the protocol does not support listening on an unbound socket. 95.\" ========== 96.It Bq Er EINVAL 97.Fa socket 98is already connected. 99.\" ========== 100.It Bq Er ENOTSOCK 101The argument 102.Fa socket 103does not reference a socket. 104.\" ========== 105.It Bq Er EOPNOTSUPP 106The socket is not of a type that supports the operation 107.Fn listen . 108.El 109.Sh SEE ALSO 110.Xr accept 2 , 111.Xr connect 2 , 112.Xr connectx 2 , 113.Xr socket 2 114.Sh BUGS 115The 116.Fa backlog 117is currently limited (silently) to 128. 118.Sh HISTORY 119The 120.Fn listen 121function call appeared in 122.Bx 4.2 . 123