Failed to verify whole-file signature while rooting on Moto 2G XT1064
Your on Marshmallow, you need to do some extra steps...

First, install TWRP 3.0 or higher, or be able to boot it one time, and you need to have SuperSU 2.76 or 2.78 (even #'s are stable versions) on the device.

Start TWRP, go to Advanced - Terminal and enter 

echo SYSTEMLESS=true&gt;&gt;/data/.supersu and press ENTER

Then exit and go back to home and Install SuperSU normally.