Original post is here.

Before beginning, you’ll want to install the Android SDK tools onto your computer so you can use tools such as fastboot and adb. Otherwise, you won’t be able to communicate with your Nexus device.  On Gentoo this is done by adding dev-util/android-tools to /etc/portage/package.keywords and then emerge -av dev-util/android-tools.

Unlocking the Nexus device is really simply. Boot it up into fastboot mode — on the Nexus 4, this is done by holding the Power + Volume Down buttons at the same time. Once you see a screen like above, open up a command line terminal and (assuming you’re using Linux; adjust slightly as appropriate for other operating systems) type fastboot devices. If anything appears from this command, the computer recognizes the Nexus device. Then, type fastboot oem unlock, and accept the warning shown on the Nexus device by navigating with the Volume Buttons and accepting with the Power button. Congratulations, your Nexus device is now unlocked!

Rooting manually is a little tricky, because rooting the stock version of Android (the one that Google provided that originally came with the device) used to be pretty tricky. At least with a Nexus device, you just need to download a flashable CF-Auto-Root file and flash that onto the device, giving you root access. However, you’re still most likely going to need to use a custom recovery, and while you’re at it you may as well install a custom ROM onto your device (which won’t require an additional flash of CF-Auto-Root).

Unrooting your device is nearly impossible to do without flashing stock back onto your device. You’ll need to download the latest factory image from Google’s Android Developer Images site, and move the two included .img files from the .zip into a separate folder, and then open the secondary .zip and move those .img files into the same separate folder as well.

Then type the following commands into your computer while it is connected to the Nexus device:

1. fastboot devices (to make sure that the computer sees your Nexus 4)
2. fastboot flash bootloader bootloader_xxxx.img (Replace bootloader_xxxx.img with the actual file name)
3. fastboot reboot-bootloader
4. fastboot flash radio radio_xxxx.img (Replace radio_xxxx.img with the actual file name. For Android 4.3, the version should end in a .84)
5. fastboot reboot-bootloader
6. fastboot flash system system.img
7. fastboot flash userdata userdata.img
8. fastboot flash boot boot.img
9. fastboot flash recovery recovery.img
10. fastboot format cache (to remove any old traces of the old system)
11. OPTIONAL: fastboot oem lock (this re-locks the bootloader to prevent future tinkering with the device, i.e. forces you to “unlock” the bootloader again and wipe the device before tinkering)
12. fasboot reboot

Conclusion

You should now be back to a completely stock configuration for your Nexus device! Playing around with a Nexus device is a lot of fun, and it provides a great learning experience about how to tinker with Android. Above all, it can provide a lot of extra functionality (such as LTE functionality on the Nexus 4) that isn’t built into Android itself — you just have to go find it yourself.