While I do not claim to be an expert here, I am concerned that this answer will not result in a persistent permission change over a reboot, and/or the usb cable from the UPS gets moved to a different port.
Following the information from here: Musings of the Nannerpuss: NUT - Network UPS Tools - on Ubuntu .
"... The problem involves the fact that Ubuntu mounts the device as owned by root, but the nut daemon drops to an unprivileged account that doesn't have the necessary access. The simple fix is to use udev to adjust the device permissions.
Connect the device and (as root) run lsusb and locate it. Note the Bus and Device IDs as well as the Vendor:Product ID pair...."
using output as in above answer:
$ lsusb
Bus 002 Device 004: ID 051d:0002 American Power Conversion Uninterruptible Power Supply
again from the link "... You can create a udev rule that controls the mount behavior at boot: ..." (edited to match this scenario better)"
- use your favourite text editor to make (most likely) a new udev rules.d file. The number must be higher than any other udev.d rules file for the same action:
for example
sudo nano /etc/udev/rules.d/90-nut-ups.rules
# /etc/udev/rules.d/90-nut-ups.rules
ACTION=="add", \
SUBSYSTEM=="usb", \
ATTR{idVendor}=="051d", ATTR{idProduct}=="0002", \
MODE="0660", GROUP="nut"
The rule watches for USB device additions with a vendor and product that match the UPS. It then sets the mode to 0660 and the group to nut instead of the default root.
Note that this answer uses 660 permission rather than 666 since that should be sufficient and more secure.
Reload udev (reboot, or perhaps unplugging then re plugging the usb cable from the UPS at the pc port), then disconnect and reconnect the device and test that the new permissions are correct. I an unclear on this part. In any case, once the nut user group has read and write on the device, it should be able to start successfully.
The udev rules.d edit did work on my 12.04.2 system even when I moved the USB cable to a different port, resulting in different Bus Device numbers on the lsusb output. Udev handled all without intervention. In fact, I may not have had to reboot when I moved it but can't remember for sure and will leave that testing to someone else.