redhat man page for listen

LISTEN(2)						     Linux Programmer's Manual							 LISTEN(2)

NAME
       listen - listen for connections on a socket

SYNOPSIS
       #include <sys/socket.h>

       int listen(int s, int backlog);

DESCRIPTION
       To  accept connections, a socket is first created with socket(2), a willingness to accept incoming connections and a queue limit for incom-
       ing 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 succeed.

NOTES
       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.  When syncookies are enabled there is no logical maximum length and this sysctl
       setting is ignored.  See tcp(7) for more information.

RETURN VALUE
       On success, zero is returned.  On error, -1 is returned, and errno is set appropriately.

ERRORS
       EADDRINUSE
	      Another socket is already listening on the same port.

       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 listen operation.

CONFORMING TO
       Single Unix, 4.4BSD, POSIX 1003.1g draft. The listen function call first appeared in 4.2BSD.

BUGS
       If the socket is of type AF_INET, and the backlog argument is greater than the constant SOMAXCONN (128 in Linux 2.0 & 2.2), it is  silently
       truncated to SOMAXCONN.	Don't rely on this value in portable applications since BSD (and some BSD-derived systems) limit the backlog to 5.

SEE ALSO
       accept(2), connect(2), socket(2)

BSD Man Page							    1993-07-23								 LISTEN(2)