listen - phpMan

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  speci-
       fied 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 appropri-
       ately.

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 con-
       stant  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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