Android - gdamjan/gdamjan.github.io GitHub Wiki
Typically recovery is flashed via fastboot (fastboot flash recovery ...img) but for some reason it's not working on mine (FAILED (remote: not allowed)). Probably I need to reflash the HBOOT bootloader with an unlocked one. Luckily it can be flashed from android itself:
$ sudo adb shell su - flash_image recovery /sdcard/download/openrecovery-TWRP-ace-2.8.6.0-unofficial.img
For some reason boot.img needs to be reflashed: fastboot flash boot boot.img