How to raise failed network interfaces after upgrade to Ubuntu 16.04
In 16.04, because of persistent naming, your interface is probably no longer eth0. Check:
ifconfig
For example, my ethernet interface is now enp0s25. Correct your /etc/network/interfaces file as needed and then:
sudo ifdown enp0s25 && sudo ifup enp0s25
Of course, substitue your interface name as needed.
Why is enp#s# in stead of eth# ? Whats the meaning of enp#s#?