listen(3p) — Linux manual page


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

       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.1‐2017, sys_socket.h(0p)

COPYRIGHT         top

       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 .

       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               2017                        LISTEN(3P)

Pages that refer to this page: sys_socket.h(0p)accept(3p)bind(3p)socket(3p)