cat /etc/network/interfaces No such file or directory
Since version 18.04 Ubuntu by default uses netplan to configure network.
Go to /etc/netplan, here you will find your network configuration.
It will look something like this:
00-installer-config.yaml
# This is the network config written by 'subiquity'
network:
ethernets:
ens18:
dhcp4: true
version: 2