ubuntu@cx1640-1:/etc/apt/sources.list.d$ sudo apt-get update
Hit:1 http://us.archive.ubuntu.com/ubuntu xenial InRelease
Hit:2 http://archive.ubuntu.com/ubuntu zesty InRelease                                        
Hit:3 http://ppa.launchpad.net/hardware-certification/public/ubuntu xenial InRelease          
Hit:4 http://us.archive.ubuntu.com/ubuntu xenial-updates InRelease      
Hit:5 http://us.archive.ubuntu.com/ubuntu xenial-security InRelease
Reading package lists... Done