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LISTEN(2)                   BSD System Calls Manual                  LISTEN(2)

NAME
     listen -- listen for connections on a socket

SYNOPSIS
     #include <&lt;sys/socket.h>&gt;

     int
     listen(int s, int backlog);

DESCRIPTION
     To accept connections, a socket is first created with socket(2), a will-
     ingness to accept incoming connections and a queue limit for incoming
     connections are specified 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 may succeed.

RETURN VALUES
     Upon successful completion, the value 0 is returned; otherwise the
     value -1 is returned and the global variable errno is set to indicate the
     error.

ERRORS
     listen() will fail if:

     [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 opera-
                        tion listen().

     [EINVAL]           The socket is already connected.

SEE ALSO
     accept(2), connect(2), socket(2), sysctl(8)

STANDARDS
     The listen() function conforms to IEEE Std 1003.1-2008 (``POSIX.1'').

HISTORY
     The listen() system call first appeared in 4.1cBSD.

BUGS
     The backlog is currently limited (silently) to the value of the
     kern.somaxconn sysctl, which defaults to 128.

BSD                            December 10, 2014                           BSD