When upgrading: Setting up ifupdown (0.8.36+nmu1) ... Installing new version of config file /etc/init.d/networking ... ifupdown.postinst: Warning: /etc/network/interfaces does not exist I now use NetworkManager by default, so that /etc/network/interfaces is not necessary. And AFAIK, the network can also be managed by systemd. (I'm not sure whether ifupdown is still useful, but I think that the ifup and ifdown commands may become necessary in case of issue with NetworkManager.)