I have a UPS connected to my freenas box, and using NUT and UPSC I can monitor the battery level on my centos 7 host.

In the case of an emergency, and my UPS goes below, lets say 40% battery, I would like to make a script to shutdown all running VMs, and then reboot the host.  

Otherwise I am afraid of sending a straight reboot command to the host without taking care of the virtual machines first.

Thanks!