Installation aborted when trying to adb sideload to Nexus 7 for upgrading to Lollipop I have a Nexus 7 2012 device and I am attempting to upgrade to lollipop.  I can get the right image from:

https://developers.google.com/android/nexus/images

However, when I try to upgrade from 4.4.2, I run the command: 

adb sideload lollipop.zip

The file gets uploaded, but the device then says: 

Verifing the update package:
E: Footer is wrong
E. Signature Verification Failed
Installation aborted.

I tried both images for the 2012 Wifi and Mobile versions, same result. I also tried to do a factory reset.

Are the images wrong, or am I just doing something wrong?
The factory images provided on that page are not packaged for installation via Android's recovery system. You'll need to use the flashing instructions to install the images using fastboot. If your device's bootloader is not unlocked already, this would require wiping all of your data. If it is unlocked, then you can skip the wipe by flashing just the bootloader upgrade, the the system image, and the boot image:

fastboot flash bootloader
fastboot reboot-bootloader
fastboot flash boot /path/to/boot.img
fastboot flash system /path/to/system.img


The alternative would be to incrementally apply the OTA updates for your device up to the latest version. These are designed to work in recovery mode, but need to be applied in order from earliest to latest since they are patch updates, not full system images. The Nexus 7 Wi-Fi OTA updates can be obtained from Google's servers using the following links:


KOT49H (4.4.2) to KTU84L (4.4.3)
KTU84L to KTU84P (4.4.4)
KTU84P to LRX21P (5.0)
LRX21P to LRX22G (5.0.2)
LRX22G to LMY47D (5.1)


For the GSM-enabled version, you can use these links:


KOT49H to KTU84L
KTU84L to KTU84P
KTU84P to LRX22G
The 2012 Nexus 7 GSM has not received a 5.1 OTA yet. You must currently use the factory images if you want to update to 5.1.


Additional OTA links can be found in this XDA thread, if needed.