How to install SuperSU V2.78 on a Nexus 6P
Before we get started, please, make sure that your phone is unlocked and connected to a PC.
You will need the following tools:
Steps:Download the TWRP recovery (Download it here). Download SuperSU 2.78 (the zip file). Reboot your Nexus to bootloader. In prompt command, type in: fastboot flash recovery recovery.img. After flashing in the recovery.img, reboot to recovery mode. In TWRP, click “advanced”----“adb sideload”---- and swipe to proceed. Type in, from the prompt command: adb sideload SuperSU2.78.zip. Wait for the phone to reboot and VOILÀ! SuperSU will be right there on your screen.