| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON | The Linux Programming Interface |
LISTEN(2) Linux Programmer's Manual LISTEN(2)
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.
EADDRINUSE
Another socket is already listening on the same port.
EBADF The argument sockfd is not a valid descriptor.
ENOTSOCK
The argument sockfd is not a socket.
EOPNOTSUPP
The socket is not of a type that supports the listen() operation.
4.4BSD, POSIX.1-2001. The listen() function call first appeared in 4.2BSD.
To accept connections, the following steps are performed:
1. A socket is created with socket(2).
2. The socket is bound to a local address using bind(2), so that other
sockets may be connect(2)ed to it.
3. A willingness to accept incoming connections and a queue limit for
incoming connections are specified with listen().
4. Connections are accepted with accept(2).
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 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.
See bind(2).
accept(2), bind(2), connect(2), socket(2), socket(7)
This page is part of release 3.32 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/.
Linux 2008-11-20 LISTEN(2)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface