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.\"     @(#)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
.B 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 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), " connect "(2), " socket (2)