After installing a fresh Ubuntu, you might run into a problem with the network manager, which will not allow you to remove or edit the ifupdown connection.
Even when you manage to configure your own connection, Ubuntu might sometimes jump back to the ifupdown connection. This is bad if you need to configure your internet conection manually.
To solve the problem, edit the interfaces file located in /etc/network/ – to do this, open up a terminal by hitting CTRL+ALT+T, then paste the below command:
sudo gedit /etc/network/interfaces
This will open the interfaces file in gedit. Now remove everything, except the below:
auto lo iface lo inet loopback
Finally, edit the NetworkManeger.conf file located in /etc/NetworkManeger/, then locate and set maneged to false – if its not already set to false. The file´s content should be similar to the below:
[main] plugins=ifupdown,keyfile,ofono dns=dnsmasq [ifupdown] managed=false