This is for Linux Mint (Debian), I assume other distros will be similar:
If you are using dfu-programmer, “reset” probably doesn’t work. You
need to do it twice, the second one will report a failure but will
actually reset the device. Go figure.
The following udev rule, placed in /etc/udev/rules.d/99-avr,rules will
give non-root users permission to program the device with
dfu-programmer. Note the 99- prefix on the reules file is essential,
because the default rules in /lib/udev/rules.d/91-permissions.rules
assign restrictive permissions, and the rule files are processed in
lexical order. If your AVR rules file starts with something
lexographically lower, any device permissions it sets will be
overwritten when the 91-permissions.rules file is processed. Yes, it
took an age for me to figure that out 
SUBSYSTEM==“usb”, ACTION==“add”, ATTR{idVendor}==“03eb”,
ATTR{idProduct}==“2ff0”, MODE=“0666”
Alan Burlison