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.
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 opera-
SVr4, 4.4BSD (the listen function call first appeared in
If the socket is of type af_inet, and the backlog argument
is greater than the constant SO_MAXCONN (128 in 2.0.23), it
is silently truncated to SO_MAXCONN. For portable applica-
tions don't rely on this value since BSD (and at least some
BSD derived systems) limit the backlog to 5.
accept(2), connect(2), socket(2)