I am building Android from source in order to install my company's custom filesystem (Datalight Reliance Nitro). I'm using an Ubuntu 12.04 PC as my host device and a Nexus 7 (flo) as my Android device. I have followed the instructions for setting up the the host system, including setting up the file /etc/udev/rules.d/51-android.rules.
I had been building Android 4.4.3, and ADB ran just fine as expected. (No need for sudo privileges.)
However, when I built and installed Android 5.1.1, suddenly ADB complains:
$ adb devices List of devices attached ???????????? no permissions
I tried several further mods to my 51-android.rules file, but no success. Following CyanogenMod's instructions on the topic, I finally ran the ADB server on sudo, and that worked. But I'm wondering why. How could the version of Android effect the privileges ADB needs? Or am I possibly overlooking something else entirely?