If you're looking for the Android 4.2.2 update for the Nexus 7 3G, good news: we've got the link to download it from Google's servers (download). To get a sense of what's new in Android 4.2.2, check out our post on the new features here. And if you want an even deeper dive into the changes, you can check out the developer changelog here.
So, how do you go about flashing the Android 4.2.2 update to your Nexus 7 3G right now, instead of waiting for it to be pushed to your device over the air? Well, just keep reading, and you'll find out. Note: If you have a regular Nexus 7 Wi-Fi, these instructions will still work, but you'll need a different update file, which you can find here.
The short version: get your Nexus 7 into recovery, hook it up via USB, and select "apply update from adb," then use the 'adb sideload [FULL UPDATE FILE NAME HERE]' command. If you have a custom recovery, you should be able to apply the update in the normal way (straight from the zip file on device storage).
The long version:
Prerequisite: Your Nexus 7 3G should be running Android 4.2.1 build JOP40D. You will not lose your data using this method.
Download the update zip from Google's servers.
If you have a custom recovery, you can just copy it to the device, reboot to recovery, and flash directly as you would any other zip. You're done.
If you have the stock recovery, carry on.
Reboot your Nexus 7 and hold the VolDn button while it's booting up. Once you see the fastboot menu and the word Start, press VolUp a few times until you see Recovery and then press the Power button to enter recovery.
You will see an Android with a red exclamation point. Now press VolUp+Power together, and you should see the menu below.
Select the 2nd option called apply update from adb.
Connect the Nexus 7 to your computer with a USB cable.
Make sure you have a recent version of adb that supports the sideload command (if you don't, download the latest Android SDK to ensure your adb is up-to-date).
Keep the file you just downloaded on your computer and open up a command prompt (cmd in Windows, regular shell in Linux and Mac) in the same directory as the zip file.
adb sideload 357318e165a8.signed-nakasig-JDQ39-from-JOP40D.357318e1.zip
You should see the progress bar go up to 100%, like so:
sending: 'sideload' 100%
At this point, the device should have started installing the update.
Reboot - you're done. Enjoy Android 4.2.2 on your Nexus 7!