listen

 

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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 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  syn-
        cookies 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 lis-
               ten operation.
 
 CONFORMING TO
        Single Unix, 4.4BSD, POSIX 1003.1g draft. The listen func-
        tion 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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