listen — listen for connections on a socket
#include <sys/types.h> /* See NOTES */ #include <sys/socket.h>
int
listen( |
int | sockfd, |
int | backlog) ; |
To accept connections, a socket is first created with
socket(2), a willingness to
accept incoming connections and a queue limit for incoming
connections are specified with listen
(), and then the connections are
accepted with accept(2). The listen
() call applies only to sockets of
type SOCK_STREAM
or
SOCK_SEQPACKET
.
The 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 ECONNREFUSED or,
if the underlying protocol supports retransmission, the
request may be ignored so that retries succeed.
On success, zero is returned. On error, −1 is
returned, and errno
is set
appropriately.
Another socket is already listening on the same port.
The argument sockfd
is not a valid
descriptor.
The argument sockfd
is not a
socket.
The socket is not of a type that supports the
listen
() operation.
POSIX.1-2001 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
parameter 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 the tcp_max_syn_backlog
sysctl.
When syncookies are enabled there is no logical maximum
length and this sysctl setting is ignored. See tcp(7) for more
information.
If the backlog
argument is greater than the value in /proc/sys/net/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 2.70 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.
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. $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> |