Insufficient permissions for device in Android Studio Workspace running in openSUSE 13.2

I had this while using a Linux machine with a Nexus 4 running Android 5.1

The fix was to enable both 'debug over USB' and 'connect as MTP'. The opposite is true when using the same device and Android Studio and adb on OSX though - to allow Android Studio to recognise the handset, I need to disable 'connect as MTP'.

I found a simple answer that worked for me:

adb kill-server
sudo adb start-server
sudo adb devices

You will find your device then. Hope this helps.

Reference: http://itsfoss.com/fix-error-insufficient-permissions-device/

It's simple. Just change your USB mode to File Transfer mode then it works.