There are a few unique ways people can become root users on the Google Nexus 6P smartphone running on the Android 6.0.1 Marshmallow software updates. Sometimes you will need to unlock the bootloader on the smartphone so that you can install a custom recovery first. The bootloader is what runs the Android operating system, and it is responsible for choosing what mode to boot the device into next. Naturally, it is programmed how to think which is to boot directly into the Android OS and not to allow a custom recovery to be installed. We can change the way the device thinks so that the bootloader is not only unlocked but it will boot into the custom recovery too. Other ways include installing a one-click rooting tool that can handle everything for you which is usually installing and enabling the SuperSU or KingUser. Other times people can become root users by installing a custom ROM which already comes pre-rooted. While it’s true, some custom ROMs require you to be rooted before you can install them, the one’s that come pre-rooted usually do not since they come rooted for you anyhow.
- The following guide is made for the Google Nexus 6P smartphone and not any other. The guide makes use of a custom recovery which is only able to be installed on the Nexus 6P smartphone. Attempting to install the same file on any other device will probably result in that device getting bricked.
- You must have a custom recovery installed on the Google Nexus 6P smartphone  before you can use this guide to install the SuperSU on the phone. Make sure you unlock the bootloader on the Google Nexus 6P smartphone before you install the custom recovery. Only installing the SuperSU application from the Google Play Store is not going to result in it enabling root users for it to result in you becoming a root user.
BEFORE WE BEGIN
- You must have the Developer Options unlocked on the Google Nexus 6P smartphone before you can turn on the USB Debugging Mode, which is a requirement for you to be able to do some developments to the software on your phone. You can do that on the Google Nexus 6P smartphone by tapping on the Menu > Settings > About Device > Build Number, and keep tapping on the build number available until it gives you a new message on the display that says you are using the smartphone as a developer now.
- Enter the Developer Options menu and then enable the USB Debugging Mode, so you are ready to start with the guide. You can do that on the Nexus 6P by tapping on the Menu > Settings > Developer Options > USB Debugging Mode.
HOW TO ROOT GOOGLE NEXUS 6P SMARTPHONES RUNNING ON MTC19V ANDROID 6.0.1 MARSHMALLOW
- Download the SuperSU version that roots the Google Nexus 6P smartphone when it is running on the MTC19V firmware from here .
- Connect the Google Nexus 6P smartphone to the computer with the USB cable that you usually use to charge the battery on the device.
- Copy the SuperSU zip file from the desktop over to the internal storage SD card.
- Unplug the Google Nexus 6P smartphone from the computer and reboot the Google Nexus 6P into the recovery mode so that the custom recovery boots up on the display.
- Tap on the ‘Backup’ option from the main custom recovery menu and proceed to take the NANDroid Backup.
- Tap on the ‘Install’ option from the main custom recovery menu and then browse the SD card for the SuperSU zip file that the recovery is going to install and enable to give you the root access.
- Select the option that says it will reboot the system from the main TWRP menu once the device is rooted.
In conclusion, that is how to root the Google Nexus 6P Android 6.0.1 Marshmallow when it is running on the MTC19V firmware build numbers. The Nexus 6P smartphone will now reboot back into the normal mode where you can enter the Google Play Store and then start downloading the applications that require root access to run. Moreover, since you already have installed TWRP on the Google Nexus 6P smartphone, you can boot into the custom recovery and then install custom ROMs.