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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 sockfd, 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 sockfd is not a valid descriptor.

       ENOTSOCK
	      The argument sockfd is not a socket.

       EOPNOTSUPP
	      The socket is not of a type that supports	 the  listen()	opera-
	      tion.

CONFORMING TO
       4.4BSD,	POSIX.1-2001.	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.

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



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