listen - listen for connections on a socket
int listen(int s, 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 may succeed.
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; see tcp(4).
When syncookies are enabled there is no logical maximum
length and this sysctl setting is ignored.
On success, zero is returned. On error, -1 is returned,
and errno is set appropriately.
EBADF The argument s is not a valid descriptor.
The argument s is not a socket.
The socket is not of a type that supports the lis
SVr4, 4.4BSD (the listen function call first appeared in
If the socket is of type AF_INET, and the backlog argument
applications, don't rely on this value since BSD (and some
BSD-derived systems) limit the backlog to 5.
accept(2), connect(2), socket(2)