LISTEN(2) BSD System Calls Manual LISTEN(2)
listen -- listen for connections on a socket
listen(int s, int backlog);
To accept connections, a socket is first created with socket(2), a will-
ingness 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.
Upon successful completion, the value 0 is returned; otherwise the
value -1 is returned and the global variable errno is set to indicate the
listen() will fail if:
[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 opera-
[EINVAL] The socket is already connected.
accept(2), connect(2), socket(2), sysctl(8)
The listen() function conforms to IEEE Std 1003.1-2008 (``POSIX.1'').
The listen() system call first appeared in 4.1cBSD.
The backlog is currently limited (silently) to the value of the
kern.somaxconn sysctl, which defaults to 128.
BSD April 29, 2017 BSD