Network UPS Tools User Manual

Network UPS Tools User Manual 34 / 84
Establishing timers
Let’s say that you want to receive a page when any UPS has been running on battery for 30 seconds. Create a handler that starts
a 30 second timer for an ONBATT condition.
AT ONBATT * START-TIMER onbattwarn 30
This means "when any UPS (the *) goes on battery, start a timer called onbattwarn that will trigger in 30 seconds". We’ll come
back to the onbattwarn part in a moment. Right now we need to make sure that we don’t trigger that timer if the UPS happens to
come back before the time is up. In essence, if it goes back on line, we need to cancel it. So, let’s tell upssched that.
AT ONLINE * CANCEL-TIMER onbattwarn
Executing commands immediately
As an example, consider the scenario where a UPS goes onto battery power. However, the users are not informed until 60 seconds
later - using a timer as described above. Whilst this may let the logged in users know that the UPS is on battery power, it does not
inform any users subsequently logging in. To enable this we could, at the same time, create a file which is read and displayed to
any user trying to login whilst the UPS is on battery power. If the UPS comes back onto utility power within 60 seconds, then we
can cancel the timer and remove the file, as described above. However, if the UPS comes back onto utility power say 5 minutes
later then we do not want to use any timers but we still want to remove the file. To do this we could use:
AT ONLINE * EXECUTE ups-back-on-power
This means that when upsmon detects that the UPS is back on utility power it will signal upssched. Upssched will see the above
command and simply pass ups-back-on-power as an argument directly to CMDSCRIPT. This occurs immediately, there are no
timers involved.
7.2.3 Writing the command script handler
OK, now that upssched knows how the timers are supposed to work, let’s give it something to do when one actually triggers. The
name of the example timer is onbattwarn, so that’s the argument that will be passed into your CMDSCRIPT when it triggers.
This means we need to do some shell script writing to deal with that input.
#! /bin/sh
case $1 in
onbattwarn)
echo "The UPS has been on battery for awhile" \
| mail -s"UPS monitor" bofh@pager.example.com
;;
ups-back-on-power)
/bin/rm -f /some/path/ups-on-battery
;;
*)
logger -t upssched-cmd "Unrecognized command: $1"
;;
esac
This is a very simple script example, but it shows how you can test for the presence of a given trigger. With multiple ATs creating
various timer names, you will need to test for each possibility and handle it according to your desires.
Note
You can invoke just about anything from inside the CMDSCRIPT. It doesn’t need to be a shell script, either - that’s just an
example. If you want to write a program that will parse argv[1] and deal with the possibilities, that will work too.