mirror of https://github.com/mkerrisk/man-pages
138 lines
4.5 KiB
Groff
138 lines
4.5 KiB
Groff
.\" Copyright (c) 1983, 1991 The Regents of the University of California.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $Id: listen.2,v 1.6 1999/05/18 14:10:32 freitag Exp $
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.\"
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.\" Modified Fri Jul 23 22:07:54 1993 by Rik Faith <faith@cs.unc.edu>
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.\" Modified 950727 by aeb, following a suggestion by Urs Thuermann
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.\" <urs@isnogud.escape.de>
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.\" Modified Tue Oct 22 08:11:14 EDT 1996 by Eric S. Raymond <esr@thyrsus.com>
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.\" Modified 1998 by Andi Kleen
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.\" Modified 11 May 2001 by Sam Varshavchik <mrsam@courier-mta.com>
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.\"
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.TH LISTEN 2 1993-07-23 "BSD Man Page" "Linux Programmer's Manual"
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.SH NAME
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listen \- listen for connections on a socket
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.SH SYNOPSIS
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.B #include <sys/socket.h>
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.sp
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.BI "int listen(int " sockfd ", int " backlog );
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.SH DESCRIPTION
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To accept connections, a socket is first created with
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.BR socket (2),
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a willingness to accept incoming connections and a queue limit for incoming
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connections are specified with
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.BR listen (),
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and then the connections are
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accepted with
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.BR accept (2).
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The
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.BR listen ()
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call applies only to sockets of type
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.B SOCK_STREAM
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or
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.BR SOCK_SEQPACKET .
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.PP
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The
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.I backlog
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parameter defines the maximum length the queue of pending connections may
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grow to.
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If a connection request arrives with the queue full the client
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may receive an error with an indication of
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.B ECONNREFUSED
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or, if the underlying protocol supports retransmission, the request may be
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ignored so that retries succeed.
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.SH NOTES
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The behaviour of the
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.I backlog
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parameter on TCP sockets changed with Linux 2.2.
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Now it specifies the queue length for
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.I completely
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established sockets waiting to be accepted, instead of the number of incomplete
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connection requests.
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The maximum length of the queue for incomplete sockets
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can be set using the
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.B tcp_max_syn_backlog
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sysctl.
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When syncookies are enabled there is no logical maximum
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length and this sysctl setting is ignored.
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See
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.BR tcp (7)
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for more information.
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.SH "RETURN VALUE"
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On success, zero is returned.
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On error, \-1 is returned, and
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.I errno
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is set appropriately.
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.SH ERRORS
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.TP
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.B EADDRINUSE
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Another socket is already listening on the same port.
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.TP
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.B EBADF
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The argument
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.I sockfd
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is not a valid descriptor.
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.TP
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.B ENOTSOCK
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The argument
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.I sockfd
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is not a socket.
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.TP
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.B EOPNOTSUPP
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The socket is not of a type that supports the
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.BR listen ()
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operation.
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.SH "CONFORMING TO"
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4.4BSD, POSIX.1-2001.
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The
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.BR listen ()
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function call first appeared in 4.2BSD.
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.SH BUGS
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If the socket is of type
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.BR AF_INET ,
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and the
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.I backlog
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argument is greater
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than the constant
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.B SOMAXCONN
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(128 in Linux 2.0 & 2.2), it is silently truncated
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to
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.BR SOMAXCONN .
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.\" The following is now rather historic information (MTK, Jun 05)
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.\" Don't rely on this value in portable applications since BSD
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.\" (and some BSD-derived systems) limit the backlog to 5.
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.SH "SEE ALSO"
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.BR accept (2),
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.BR bind (2),
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.BR connect (2),
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.BR socket (2)
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