• Open the file manager as super user, e.g. sudo dolphin
  
  ^{Be careful with such instance of file manager because you may delete something important and break your system}


• Create a file named autoupdate in /etc/cron.* (where * is hourly, daily, weekly, monthly depending on your preference). I used /etc/cron.hourly/.



• Put the following contents into the file:

  
  
  

  #!/bin/bash
  
  apt-get update
  
  apt-get upgrade -y
  
  apt-get autoclean
  
  

  
  
  

  ... and save it.



• Allow the file to be executed in its properties, or by using this: sudo chmod 755 autoupdate

And that's it! You will have your software automatically updated without any notifications

(of course, if you've turned off the notifications in update settings).

_{Thanks to boehj for the source of information: Automatic Weekly Package Updates Using Cron And Apt-Get}