update example ntp.script

Handle an interesting corner case when NTP server is reachable...
but on a different IP now.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

examples/var_service/ntpd/ntp.script

@@ -10,12 +10,30 @@
 
 dt=`date '+%Y-%m-%d %H:%M:%S'`
 
+echo "`tail -n 199 -- "$0.log" 2>/dev/null`" >"$0.log.$$"
+
+if test x"$1" = x"unsync" \
+; then
+	# No replies for our NTP requests were seen for some time.
+	#
+	# Among more mundate cases like network outages, this happens
+	# if we ran for a LONG time (days) and ntp server's IP has changed.
+	# ntpd has no code to re-resolve peers' addresses to IPs,
+	# we need to help it:
+	#
+	echo "$dt: $1"\
+		"syncronization lost, restarting ntpd"\
+		>>"$0.log.$$"
+	mv -- "$0.log.$$" "$0.log"
+	kill $PPID
+	exit
+fi
+
 if test x"$stratum" != x"" \
 && test x"$poll_interval" != x"" \
 && test 4 -ge "$stratum" \
 && test 128 -le "$poll_interval" \
 ; then
-	echo "`tail -n 199 -- "$0.log" 2>/dev/null`" >"$0.log.$$"
 	echo "$dt: $1"\
 		"freq_drift_ppm=$freq_drift_ppm"\
 		"offset=$offset"\
@@ -27,7 +45,6 @@ if test x"$stratum" != x"" \
 	exec hwclock --systohc
 fi
 
-echo "`tail -n 199 -- "$0.log" 2>/dev/null`" >"$0.log.$$"
 echo "$dt: $1"\
 	"freq_drift_ppm=$freq_drift_ppm"\
 	"offset=$offset"\