terminal - 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).

  
  

Answer

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.