Ethernet adapter was disable on Ubuntu 17.04

Here is how to fix this problem.

Edit file /usr/lib/NetworkManager/conf.d/10-globally-managed-devices.conf and change it's content from :

[keyfile]
unmanaged-devices=*,except:type:wifi,except:type:wwan

To :

[keyfile]
unmanaged-devices=*,except:type:ethernet,except:type:wifi,except:type:wwan

And then run :

sudo service network-manager restart

That's all.

My Ethernet was also disabled after I upgraded from LTS 16.04 to 16.10 then to 17.04. I was able to resolve by manually doing the following:

sudo ifconfig eth0 up 
sudo dhclient eth0