For USB based APC or any other devices connected to your FreeNAS or FreeBSD UNIX server use the following command to determine the correct device name:
dmesg | grep -i usbus | grep -i --color 'american power conversion'
So my UPS is located at USB port /dev/ugen0.2.
A note about FreeNAS user
You can use web console. Login to your FreeNAS web-gui. Check the box “Show console messages” in System > Advanced.
Next plug in the USB device and the console messages will give the name of the /dev/ugenX.X device; where the Xâ€™s are the numbers that show on the console.