To accept connections, a socket is first created with socket(2), a backlog for incoming connections is 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_SEQPACKETfR.

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 will receive an error with an indication of ECONNREFUSED.

listen() returns:

0

on success.

-1

on failure and sets errno to indicate the error.

EBADF

s is not a valid descriptor.

ENOTSOCK

s is not a socket.

EOPNOTSUPP

The socket is not of a type that supports listen().

The backlog is currently limited (silently) to 5.