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.\" Copyright (c) 1983, 1991 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the University of
.\" California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)listen.2 6.5 (Berkeley) 3/10/91
.\"
.\" Modified Fri Jul 23 22:07:54 1993 by Rik Faith <faith@cs.unc.edu>
.\" Modified 950727 by aeb, following a suggestion by Urs Thuermann
.\" <urs@isnogud.escape.de>
.\" Modified Tue Oct 22 08:11:14 EDT 1996 by Eric S. Raymond <esr@thyrsus.com>
.\"
.TH LISTEN 2 "23 July 1993" "BSD Man Page" "Linux Programmer's Manual"
.SH NAME
listen \- listen for connections on a socket
.SH SYNOPSIS
.B #include <sys/socket.h>
.sp
.BI "int listen(int " s ", int " backlog );
.SH DESCRIPTION
To accept connections, a socket is first created with
.BR socket (2),
a willingness to accept incoming connections and a queue limit for incoming
connections are specified with
.BR listen ,
and then the connections are
accepted with
.BR accept (2).
The
.B listen
call applies only to sockets of type
.B SOCK_STREAM
or
.BR SOCK_SEQPACKET .
The
.I backlog
parameter defines the maximum length the queue of pending connections may
grow to. If a connection request arrives with the queue full the client
may receive an error with an indication of
.BR ECONNREFUSED ,
or, if the underlying protocol supports retransmission, the request may be
ignored so that retries may succeed.
.SH "RETURN VALUE"
On success, zero is returned. On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP 0.8i
.B EBADF
The argument
.I s
is not a valid descriptor.
.TP
.B ENOTSOCK
The argument
.I s
is not a socket.
.TP
.B EOPNOTSUPP
The socket is not of a type that supports the operation
.BR listen .
.SH "CONFORMING TO"
SVr4, 4.4BSD (the
.B listen
function call first appeared in 4.2BSD).
.SH BUGS
If the socket is of type af_inet, and the
.I backlog
argument is greater
than the constant SO_MAXCONN (128 in 2.0.23), it is silently truncated
to SO_MAXCONN. For portable applications don't rely on this value
since BSD (and at least some BSD derived systems) limit the backlog to
5.
.SH "SEE ALSO"
.BR accept (2),
.BR connect (2),
.BR socket (2)
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