| LISTEN(2) | System Calls Manual | LISTEN(2) | 
listen —
#include <sys/socket.h>
int
  
  listen(int
    s, int
  backlog);
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.
listen() will fail if:
EBADF]ENOTSOCK]EOPNOTSUPP]listen().listen() function call appeared in
  4.2BSD.
| December 11, 1993 | NetBSD 9.4 |