You will need the following:
- A Nexus 7 with an unlocked bootloader
- Ubuntu 12.04 Precise Pangolin on your PC
- The Ubuntu Nexus 7 Installer
sudo add-apt-repository ppa:ubuntu-nexus7/ubuntu-nexus7-installer
sudo apt-get update
sudo apt-get install ubuntu-nexus7-installer
Step 2: Connect your Nexus 7 to your PC using a USB cable.Step 3: Boot into fastboot mode.
Turn off your Nexus 7. Press and hold Volume Up + Volume Down + Power buttons until you see the Android mascot.
Step 4: Ensure no other USB-based devices are connected to your PC. Search for Ubuntu Nexus7 Installer from the Ubuntu dashboard. Launch it. Follow the on-screen instructions.
Visit the Wiki page for more info.