add custom problem detector plugin

config/plugin/check_ntp.sh

@@ -0,0 +1,23 @@
+#!/bin/bash
+
+# NOTE: THIS NTP SERVICE CHECK SCRIPT ASSUME THAT NTP SERVICE IS RUNNING UNDER SYSTEMD.
+#       THIS IS JUST AN EXAMPLE. YOU CAN WRITE YOUR OWN NODE PROBLEM PLUGIN ON DEMAND.
+
+OK=0
+NONOK=1
+UNKNOWN=2
+
+which systemctl >/dev/null
+if [ $? -ne 0 ]; then
+    echo "Systemd is not supported"
+    exit $UNKNOWN
+fi
+
+systemctl status ntp.service | grep 'Active:' | grep -q running
+if [ $? -ne 0 ]; then
+    echo "NTP service is not running"
+    exit $NONOK
+fi
+
+echo "NTP service is running"
+exit $OK