--- nut-2.6.0/server/upsd.c.alt-ipv6-optional	2010-12-24 16:24:12.000000000 +0300

+++ nut-2.6.0/server/upsd.c	2011-02-20 15:44:01.508000003 +0300

@@ -539,6 +539,19 @@ static void client_readline(ctype_t *cli

 	return;

 }

+static int ipv6_available(void)

+{

+	int sock_fd;

+

+	if ((sock_fd = socket(AF_INET6, SOCK_STREAM, IPPROTO_TCP)) < 0) {

+		upsdebug_with_errno(3, "ipv6_available: socket");

+		return 0;

+	}

+

+	close(sock_fd);

+	return 1;

+}

+

 void server_load(void)

 {

 	stype_t	*server;

@@ -546,7 +559,9 @@ void server_load(void)

 	/* default behaviour if no LISTEN addres has been specified */

 	if (!firstaddr) {

 		if (opt_af != AF_INET) {

-			listen_add("::1", string_const(PORT));

+			if (opt_af == AF_INET6 || ipv6_available()) {

+				listen_add("::1", string_const(PORT));

+			}

 		}

 		if (opt_af != AF_INET6) {