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

PROLOG         top

       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         top

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

SYNOPSIS         top

       #include <sys/socket.h>

       int listen(int socket, int backlog);

DESCRIPTION         top

       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

       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         top

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

ERRORS         top

       The listen() function shall fail if:

       EBADF  The socket argument is not a valid file descriptor.

              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.

              The socket argument does not refer to a socket.

              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.

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

       The following sections are informative.

EXAMPLES         top




RATIONALE         top




SEE ALSO         top

       accept(3p), connect(3p), socket(3p)

       The Base Definitions volume of POSIX.1‐2008, sys_socket.h(0p)

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group                 2013                          LISTEN(3P)