I have a previously rooted Nexus 5 on 4.4 and updated it recently with the Lollipop OTA. I am trying to re-root it again but it is not recognized using my Windows 7, Windows 8 or Ubuntu 14.04 machines. I have tried the WUG toolkit on windows by installing and reinstalling the drivers and adb on linux, turning on/off the Developer-usb-debugging mode, turning on-off the MTP mode. I was previously using TWRP. Now when I go to recovery mode, the phone shows "No command" with the green droid.