[Nexus 7 General] greg_gorrell:
To anyone who has had the issue of installing the OTA Kit Kat update and ended up with an error, followed by bootloop "No Command" screen, here's the fix and how to save your data. I was unable to successfully get the image flashed using adb sideload, but I will mention it as others apparently have.

When attempting to install over the air update on Nexus 7 2012, Wifi edition, about 25% into the install I received an error screen. Upon restarting device, the Nexus would load the Google splash screen, followed by a "No Command" screen. To those that have encountered this and are worried about losing your data, follow these instructions. I am using Ubuntu so you will have to do a little research on downloading the tools for Windows and how to use them. I have a ton of computers to work on and don't have much time to type out a long guide, and I have never used either of these tools on a Windows machine.

Download the factory image for Kit Kat from here: https://dl.google.com/dl/android/aosp/nakasi-krt16s-factory-da7dee49.tgz

Tools needed:

Drivers for your Nexus (Windows only)

Fastboot

ADB

Fastboot and adb are packed together in the Android SDK, or other sources have them. Using ubuntu, run "sudo apt-get install android-tools-fastboot" and "sudo apt-get install android-tools-adb" in your command line.

If you want to use adb sideload, check to make sure you device is recognized in "70-android.rules" or "51-android.rules" by running:

adb devices

If you get "?????????" then you better edit your android rules file by typing:

gksudo gedit /etc/udev/rules.d/70-android.rules

Note that your android file could use the number 51 or 99 also, so I would recommend performing this step 3 times with 70-android.rules, 51-android.rules, and 99-android.rules.

Add the following:

SUBSYSTEM=="usb", ATTRS{idVendor}=="18d1", MODE="0666", GROUP="adbusers" #regular/debug
SUBSYSTEM=="usb", ATTRS{idVendor}=="18d1", MODE="0666", GROUP="adbusers" #fastboot
SUBSYSTEM=="usb", ATTRS{idVendor}=="18d1", MODE="0666", GROUP="plugdev" #regular/debug
SUBSYSTEM=="usb", ATTRS{idVendor}=="18d1", MODE="0666", GROUP="plugdev" #fastboot

Save this file and exit your editor. Now, extract your image you downloaded from Google. You should see a file named "image-nakasi-krt16s.zip." Copy this somewhere easily accessible, such as /home/<your username>/ANDROID.

Open command prompt and enter the following:

cd /home/<your username>/ANDROID
adb sideload image-nakasi-krt16s.zip

If all goes well, this should install and reboot. If not, you may get errors such as "E:signature verification failed" or something about unexpected files. I had about 4 different errors trying this, so continue reading to fix this using fastboot.

Extract all of the contents of the downloaded image file to the /ANDROID directory we created earlier.

Power off the device. Press and hold on to the Volume down and power key altogether until you see the bootloader screen. This screen is what we know as bootloader mode or fastboot mode. Connect the device to the PC via USB cable

Open your command prompt and head to the /ANDROID directory. In case you forgot:

cd /home/<your username>/ANDROID/

Next, run the following commands in order.

fastboot erase boot

fastboot erase cache

fastboot erase recovery

fastboot erase system

Now we need to reflash the bootloader:

fastboot flash bootloader bootloader-grouper-4.23.img

Reboot the bootloader:

fastboot reboot-bootloader

Flash the 4.4 Factory Image, type:

fastboot update image-nakasi-krt16s.zip

Now sit and wait while your tablet is updated. It will restart and your apps will be optimized. Good luck!