With TWRP installed on my phone, the recently rolled out update to Lollipop failed furious.
Sadly, as I initially screwed up to backup a recovery partionion, it took me serveral hours to trace back why it failed and to find a right firmware image on the Net to roll it back to stock state. And I tried several.
This said, the
adb tool was very helpful for debugging. Recovery
logs are located in
/cache/recovery/last_log. You can get here,
if you have root access, and see, where and why it struggled. In
my case it were non-matching release keys.
Thus, if you're in same situation and happen to own rooted german Moto G (2nd generation) with wrecked recovery partition, here is a right image of a stock firmware (4.4.4):
All you need, is to boot into
adb or by
holding Volume Down and Powerbutton) and reflash back a stock
recovry firmware. None other images are required. There is no need
to wipe your phone, as widely suggested on the Web.
adb reboot bootloader fastboot flash recovery recovery.img
With this done, the upgrade went smoothly.
root however is lost, but that's ok.
If you brick your phone, it's all your fault! I'm not responsible for any damages of any kind!