How to disable GUI on armbian (revert the Desktop to server)

1. Check which Display manager that you're using currently
   cat /etc/X11/default-display-manager
   nodm should be default if you're choose auto login when setting by armbian-config
   but you're change it with lightdm or sddm, so check the display manager first.
   
   
2. Disable current display manager
   if you're using nodm
   sudo systemctl disable nodm
   if you're using lightdm
   sudo systemctl disable lightdm
   if you're using sddm
   sudo systemctl disable sddm
   
   
3. Reboot the system
   sudo reboot
   
   
4. It's should be great now~