Thank you, James. Turns out I had two problems. I edited my command definition in the commands.cfg file to match yours (I actually had that at one point, but changed it when I could not the plugin to work!) I then used the switch.cfg sample file to set up the host, group and service definitions. And that is when I discovered my second problem. After editing the nagios.cfg file to include a pointer to my ups monitoring config file I ran the verification command (/usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg) and got the same darned WARNING (null value on line 48) message I have been getting all weekend! I don't know what made me do it this time, but I decided to check the nagios.cfg file for errors. I had an error in my pointer line -- used a "-" isntead of an "=". $%&@#$*! Sigh. All is well now. Thanks again. And I ran out this morning and picked up Wolfgang Barth's book on Nagios to assist me with the rest of my configurations. <div class="gmail_quote">On Sun, Apr 12, 2009 at 10:26 PM, <<a href="mailto:jmoseley@corp.xanadoo.com">jmoseley@corp.xanadoo.com</a>> wrote: <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Remember to CC the nagios users' list... From looking at the script, it doesn't look like there are any options for setting critical/warning thresholds for temperature, load, etc. It appears they are all predefined. In that case, the command configuration would look something like: define command { command_name check_apcups command_line $USER1$/check_snmp_apcups -H $HOSTADDRESS$ -C $ARG1$ } The service check configuration would look like: <div class="im"> define service{ use generic-service host_name apc-smart-ups </div>service_description APC_STATUS check_command check_apcups!public } Obviously, you would replace 'public' above with whatever SNMP community string you have setup... The host group and host defintions you supplied earlier should be fine. Remember, this script is fairly elementary in that it appears it predetermines all the critical/warning levels for things like temp, battery capacity, input/output voltage, etc. So, there's nothing else you need to do. It will either return an 'OK' value or generate a critical or warning alert with the simple configuration above. Obviously, you could edit the script to change any of the thresholds by hardcoding them into the script, or you could modify it to accept warning/critical threshold limits as variables. <div class="im"> James Moseley </div></blockquote></div>