listen(2) -- Linux man page
NAME
listen - listen for connections on a socket
SYNOPSIS
#include <sys/socket.h>
int listen(int s, int backlog);
DESCRIPTION
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.
NOTES
The behaviour 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.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and
errno
is set appropriately.
ERRORS
- EADDRINUSE
-
Another socket is already listening on the same port.
- EBADF
-
The argument
s
is not a valid descriptor.
- ENOTSOCK
-
The argument
s
is not a socket.
- EOPNOTSUPP
-
The socket is not of a type that supports the
listen
operation.
CONFORMING TO
Single Unix, 4.4BSD, POSIX 1003.1g draft. The
listen
function call first appeared in 4.2BSD.
BUGS
If the socket is of type
AF_INET,
and the
backlog
argument is greater
than the constant
SOMAXCONN
(128 in Linux 2.0 & 2.2), it is silently truncated
to
SOMAXCONN.
Don't rely on this value in portable applications since BSD
(and some BSD-derived systems) limit the backlog to 5.
SEE ALSO
accept(2),
connect(2),
socket(2)
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