Nexus 7 (2013) “Flo” – Bootloader Unlocking, Rooting, and System Restore


Setting up ADB and Fastboot

Enable Dev Tools

As I was used to the Developer Tools being available off the bat from custom ROMs, you’ll need to enable this menu manually.

Go to “About Phone” and tap the Build information 7 times (after 5 times you’ll see a notice).

Google USB Drivers

Ensure you have the Google USB Drivers.

  • Extract the tar.gz
  • (Windows) go to Device Manager
  • The device should be listed under “Other” (the device under Mobile devices is probably the MTP media mount)
  • Browse for drivers, then find the extracted folder (and ensure “subfolders” is checked)

ADB and Fastboot Binaries

Drop the (2) binaries you got from the Android SDK ( ../sdk/platform-tools ) into an easy enough to use folder.

You can put them in your PATH environment variable or simply navigate to the folder.

RSA Key Authorization

It turns out the new ADB requires RSA key authentication (much like SSH I guess). This also means you’ll need the latest ADB lest your device may show up as “offline” through adb devices

Using the latest binary, you’ll see this if the device hasn’t authorized your key yet.

Replug in your device (with USB debugging enabled and the right USB drivers installed). You should see a notice about authorizing the RSA key for USB debugging with the thumbprint listed out.

You should now see the device with adb devices

Good Things to Know Before you Proceed / My Gotchas

Hard Power-Down

It’s been reported that people often get stuck on the boot screen “X” or have other issues. If you need to hard power down your device:

Hold VolUp+VolDwn + Power

Manually entering the bootloader

While initially power on quickly press VolDwn + Power

If TWRP asks you to install SU, don’t bother.

I made the mistake of letting TWRP automatically install SU. It did not go well to say the least.

ADB Sideload worked better for me

Using TWRP’s ADB sideload feature to install the SU was the most successful method in my case.

TWRP and “Enter Password” / Encryption

When I initially installed TWRP, it prompted me for a password. I figured a “factory” reset (dalvik/cache) wipe would do the trick, but that got me stuck in an infinite boot that I had to hard shutdown from. I ended up flashing the factory OS images over, rebooting, then installing SU.

Flashing the Default Factory Images

The factory images come in a bundled tar.tgz file. The important bits being the .img file and the .zip file. Use your favorite compression program (e.g. 7zip on windows) to extract the files.

The .bat file (windows) and .sh file (*NIX) just execute fastboot commands. I prefer to open the script files in a text editor (e.g. Notepad++, vi, nano, etc) and execute the salient commands in the shell — to ensure (a) I’m using the right fastboot binary and (b) to diagnose any issues that occur.

So, flashing the factory image would look something like this (based off the .BAT file):

Note that -w flag stands for wipe. It shouldn’t be a big deal assuming you’re going back to zero.

Overview Steps

  • Ensure the right Google USB Drivers are installed
  • Ensure your computer has the latest ADB and fastboot binaries — ensure it can talk to your Nexus 7 with its RSA key whitelisted
  • Ensure you have copies of the stock Android for your Nexus 7
  • Ensure you have the latest copy of TWRP for your Nexus 7
  • Reboot into the bootloader
  • Check that it sees your device with fastboot devices
  • Unlock the bootloader with fastboot oem unlock
  • Reboot
  • Back in the bootloader, flash TWRP fastboot recovery flash “PATH\TO\RECOVERY\IMG”
  • Reboot
  • Boot into bootloader then go into recovery -or- boot straight into recovery
  • Hopefully, you don’t get prompted for password. You can try doing a factory reset to see if this alleviates the issue. If it doesn’t, you’ll have to install the factory image.
  • Enable ADB Sideload
  • In ADB (on your machine), check adb devices
  • Push the Su ZIP with adb sideload “path\to\sufile”
  • Reboot
  • Done

Since you now have TWRP recovery, make sure to make backups. You’re also set for flashing any new, nifty ROMs as they hit stable releases (or nightlies if you’re brave).



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