Where is enp4s0 configured?

In Debian Jessie, a typical /etc/network/interfaces contains a line that looks like this:

auto eth0 allow-hotplug eth0 iface eth0 inet dhcp

This causes eth0 to be configured when ifup -a is invoked and allows DHCP to assign an IP address. However, when I open up /etc/network/interfaces in Ubuntu 16.04 (Xenial), I observe that no such directives are present:

# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback

What happened to eth0 (or its Ubuntu equivalent enp4s0)? I have Xen installed, if that makes any difference.

2 Answers

The interface just has another name, a so-called Predictable Interface Name, probably assigned after a kernel upgrade. You can work with the NIC exactly as if it was called eth[N].

This is the normal behavior when you are using an Ubuntu flavor with a desktop environment, because all the flavors (except ubuntu server) are using the gnome network manager to handle connections. You can still edit the /etc/network/interfaces file as shown here: (run ifconfig to see the connection name, because they are named different now) but then any changes you do at one connection with the gnome network manager will be ignored, so it's better use the Network Connections app (click on network applet on the panel and choose Edit Connections).