LISTEN(3)                  POSIX Programmer's Manual                 LISTEN(3)



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

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.1-2017, <sys_socket.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  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.opengroup.org/unix/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                  2017                            LISTEN(3)
