listen — listen for connections on a socket
#include <sys/types.h> /* See NOTES */ #include <sys/socket.h>
int
listen( |
int sockfd, |
int backlog); |
listen() marks the socket
referred to by sockfd
as a passive socket, that is, as a socket that will be used
to accept incoming connection requests using accept(2).
The sockfd
argument is a file descriptor that refers to a socket of type
SOCK_STREAM or SOCK_SEQPACKET.
The backlog
argument defines the maximum length to which the queue of
pending connections for sockfd may grow. If a
connection request arrives when the queue is full, the client
may receive an error with an indication of ECONNREFUSED or, if the underlying
protocol supports retransmission, the request may be ignored
so that a later reattempt at connection succeeds.
On success, zero is returned. On error, −1 is
returned, and errno is set
appropriately.
Another socket is already listening on the same port.
(Internet domain sockets) The socket referred to by
sockfd had not
previously been bound to an address and, upon
attempting to bind it to an ephemeral port, it was
determined that all port numbers in the ephemeral port
range are currently in use. See the discussion of
/proc/sys/net/ipv4/ip_local_port_range
in ip(7).
The argument sockfd is not a valid
file descriptor.
The file descriptor sockfd does not refer to
a socket.
The socket is not of a type that supports the
listen() operation.
To accept connections, the following steps are performed:
A socket is created with socket(2).
The socket is bound to a local address using bind(2), so that other sockets may be connect(2)ed to it.
A willingness to accept incoming connections and a queue limit for incoming connections are specified with
listen().Connections are accepted with accept(2).
POSIX.1 does not require the inclusion of <sys/types.h> and this header file is not required on
Linux. However, some historical (BSD) implementations
required this header file, and portable applications are
probably wise to include it.
The behavior of the backlog argument on TCP sockets
changed with Linux 2.2. Now it specifies the queue length for
completely
established sockets waiting to be accepted, instead of the
number of incomplete connection requests. The maximum length
of the queue for incomplete sockets can be set using
/proc/sys/net/ipv4/tcp_max_syn_backlog.
When syncookies are enabled there is no logical maximum
length and this setting is ignored. See tcp(7) for more
information.
If the backlog
argument is greater than the value in /proc/sys/net/core/somaxconn, then it is
silently truncated to that value; the default value in this
file is 128. In kernels before 2.4.25, this limit was a hard
coded value, SOMAXCONN, with
the value 128.
This page is part of release 4.07 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
|
Copyright (c) 1983, 1991 The Regents of the University of California. and Copyright (C) 2007, Michael Kerrisk <mtk.manpagesgmail.com> All rights reserved. %%%LICENSE_START(BSD_4_CLAUSE_UCB) 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. %%%LICENSE_END $Id: listen.2,v 1.6 1999/05/18 14:10:32 freitag Exp $ Modified Fri Jul 23 22:07:54 1993 by Rik Faith <faithcs.unc.edu> Modified 950727 by aeb, following a suggestion by Urs Thuermann <ursisnogud.escape.de> Modified Tue Oct 22 08:11:14 EDT 1996 by Eric S. Raymond <esrthyrsus.com> Modified 1998 by Andi Kleen Modified 11 May 2001 by Sam Varshavchik <mrsamcourier-mta.com> |