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RedHat 9 (Linux i386) - man page for listen (redhat section 2)

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 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 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)


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