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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 ECON-
       NREFUSED	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	estab-
       lished  sockets waiting to be accepted, instead of the number of	incom-
       plete connection	requests. The maximum length of	the queue  for	incom-
       plete  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  applica-
       tions  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)

NAME | SYNOPSIS | DESCRIPTION | NOTES | RETURN VALUE | ERRORS | CONFORMING TO | BUGS | SEE ALSO

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