The following procedure will walk you through the step-by-step process for gaining root access on the Nvidia Shield.
Note: You must have an unlocked bootloader before you can proceed with this tutorial!
A tutorial on how to unlock your Shield's bootloader can be found here.
This tutorial also assumes how have the correct ADB and Fastboot drivers installed for your device, for a tutorial on how to install the ADB and Fastboot drivers for the Shield please look here.
Due to the nature of modifying devices system files the standard XDA disclaimer applies: I take no responsibility for bricked devices due to the following rooting procedure, no warranty express or implied is given, I will not be held responsible if you mess up your device by following this procedure!
Before you begin please make sure to read and re-read the whole procedure, making sure you understand the directions.
1. Download the "Superuser-su.zip" file and the "roth-insecure-boot-63.img" file that are attached to this post. After you have downloaded the files, extract the contents of the "Superuser-su.zip" file which contains Superuser.apk and the su binary, and move them to your ADB and Fastboot folder on your computer. Also transfer the "roth-insecure-boot-63.img" to your computer's ADB and Fastboot folder.
MD5 Checksum for "roth-insecure-boot-63.img": F8BA5C48D0323D99E2A748C77BF647F6
2. Connect your Shield to your computer using your USB cable. For maximum reliability please connect the USB cable to a USB 2.0 port directly connected to the motherboard as USB ports on the front of a case panel or USB 3.0 ports can sometimes be unreliable.
3. Now that your Shield is connected to your computer make sure that "USB debugging" is enabled under the Developer Options section in the system settings menu (If the Developer Options section is hidden, go to the About Phone/About Tablet section of the system settings and then tap on the item that lists the Build number 7 times or until it says "You are now a developer" and the Developer Options section becomes visible in the system settings).
4. Open a command prompt window (cmd) in your ADB and Fastboot folder on your computer and issue the following commands (If you are new to using ADB and Fastboot I would recommend checking out this excellent guide to get you up and running):
adb reboot bootloader
Now we will be booting an insecure boot.img (ro.secure = 0) to our device to allow us to gain root acess:
fastboot boot roth-insecure-boot-63.img
5.First we need to mount the /system partition as read/write so we can modify it:
adb shell mount -o rw,remount -t ext4 /dev/block/platform/sdhci-tegra.3/by-name/APP /system exit
adb push su /system/xbin adb push Superuser.apk /system/app adb shell chmod 6755 /system/xbin/su chmod 644 /system/app/Superuser.apk mount -o ro,remount -t ext4 /dev/block/platform/sdhci-tegra.3/by-name/APP /system sync reboot
Credits: Koush for his open source Superuser.apk and the su binary (https://github.com/koush/Superuser)
If users would like me to create a 1-click root process of this please let me know and I will do so .
If you are stuck with the rooting procedures I would recommend checking out this great video tutorial by wwjoshdew.