| 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 3.51 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)
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