PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

NAME

       listen — listen for socket connections and limit the queue of incoming connections

SYNOPSIS

       #include <sys/socket.h>

       int listen(int socket, int backlog);

DESCRIPTION

       The listen() function shall mark a connection-mode socket, specified by the socket argument, as accepting
       connections.

       The  backlog  argument  provides a hint to the implementation which the implementation shall use to limit
       the number of outstanding connections in the socket's listen queue. Implementations may impose a limit on
       backlog and silently reduce the specified value. Normally, a larger backlog argument value  shall  result
       in  a  larger  or equal length of the listen queue. Implementations shall support values of backlog up to
       SOMAXCONN, defined in <sys/socket.h>.

       The implementation may include incomplete connections in its listen queue. The limits on  the  number  of
       incomplete connections and completed connections queued may be different.

       The  implementation  may  have  an  upper  limit  on  the length of the listen queue—either global or per
       accepting socket. If backlog exceeds this limit, the length of the listen queue is set to the limit.

       If listen() is called with a backlog argument value that is less than 0, the function behaves  as  if  it
       had been called with a backlog argument value of 0.

       A  backlog  argument  of  0  may  allow the socket to accept connections, in which case the length of the
       listen queue may be set to an implementation-defined minimum value.

       The socket in use may require the process to have appropriate privileges to use the listen() function.

RETURN VALUE

       Upon successful completions, listen() shall return 0; otherwise, −1 shall be returned and  errno  set  to
       indicate the error.

ERRORS

       The listen() function shall fail if:

       EBADF  The socket argument is not a valid file descriptor.

       EDESTADDRREQ
              The  socket  is  not  bound  to a local address, and the protocol does not support listening on an
              unbound socket.

       EINVAL The socket is already connected.

       ENOTSOCK
              The socket argument does not refer to a socket.

       EOPNOTSUPP
              The socket protocol does not support listen().

       The listen() function may fail if:

       EACCES The calling process does not have appropriate privileges.

       EINVAL The socket has been shut down.

       ENOBUFS
              Insufficient resources are available in the system to complete the call.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       accept(), connect(), socket()

       The Base Definitions volume of POSIX.1‐2008, <sys_socket.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition,
       Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open  Group  Base
       Specifications  Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc
       and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In  the  event
       of  any  discrepancy between this version and the original IEEE and The Open Group Standard, the original
       IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at
       http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have  been  introduced
       during   the   conversion  of  the  source  files  to  man  page  format.  To  report  such  errors,  see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2013                                        LISTEN(3POSIX)