adb device always unauthorized Im running Ubuntu 16.04

adb version
Android Debug Bridge version 1.0.32


However, when I plug in my devices for testing via ADB I always get an unauthorized error.

adb devices

List of devices attached 
LGD855a1098057  unauthorized


adb works flawlessly on Windows 7 x64 SP1with Koushik Douttas Universal ADB driver and my friends Macbook , this singles out the Ubuntu 16.04 as the problem. 

Things I have tried:


I tried revoking previous USB authorizations.


Nothing happened.


Switching adb debugging on and off.


However, the CLI just keeps mocking me with the unauthorized error.


Switching ports.


Each port on my 16 port development rig has been tried. 


Updating adb.

android-tools-adb is already the newest version (5.1.1r36+git20160322-0ubuntu3).
android-tools-fastboot is already the newest version (5.1.1r36+git20160322-0ubuntu3).
Same problem here with exact same linux ubuntu version.

The solution for me that work well is

1 - adb kill-server

2 - sudo adb usb

after this you mobile will ask for authorization and work well.
so, adb needs root privilege.