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



NAME
       listen(1,2,7) - listen(1,2,7) for connections on a socket(2,7,n)

SYNOPSIS
       #include <sys/socket.h>

       int listen(1,2,7)(int s, int backlog);

DESCRIPTION
       To  accept(2,8)  connections,  a  socket(2,7,n)  is first created with socket(2,7,n)(2), a
       willingness to accept(2,8) incoming connections and a queue(1,3) limit for incom-
       ing connections are specified with listen(1,2,7), and then the connections are
       accepted with accept(2,8)(2).  The listen(1,2,7) call applies only  to  sockets  of
       type SOCK_STREAM or SOCK_SEQPACKET.

       The  backlog  parameter defines the maximum length the queue(1,3) of pending
       connections may grow to.  If a  connection  request  arrives  with  the
       queue(1,3)  full the client may receive an error(8,n) with an indication of ECON-
       NREFUSED or, if(3,n) 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(1,3)  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(1,3)  for  incom-
       plete  sockets  can  be set(7,n,1 builtins) using the tcp_max_syn_backlog sysctl.  When
       syncookies are enabled there is no  logical  maximum  length  and  this
       sysctl(2,5,8) setting is ignored.  See tcp(7) for more information.


RETURN VALUE
       On  success,  zero is returned.  On error(8,n), -1 is returned, and errno is
       set(7,n,1 builtins) appropriately.

ERRORS
       EADDRINUSE
              Another socket(2,7,n) 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(2,7,n) is not of a type that supports the listen(1,2,7)  operation.

CONFORMING TO
       Single  Unix,  4.4BSD,  POSIX  1003.1g  draft. The listen(1,2,7) function call
       first appeared in(1,8) 4.2BSD.

BUGS
       If the socket(2,7,n) is of type AF_INET, and the backlog argument  is  greater
       than  the  constant  SOMAXCONN (128 in(1,8) Linux 2.0 & 2.2), it is silently
       truncated to SOMAXCONN.  Don't rely on this value in(1,8) portable  applica-
       tions  since BSD (and some BSD-derived systems) limit the backlog to 5.

SEE ALSO
       accept(2,8)(2), connect(2), socket(2,7,n)(2)



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

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