ubuntu 18.04 dns settings code example
Example 1: resolvconf set dns
sudo systemctl disable systemd-resolved.service
sudo gedit /etc/resolvconf/resolv.conf.d/head
# add
nameserver 8.8.8.8
nameserver 8.8.4.4
sudo resolvconf --enable-updates
sudo resolvconf -u
Example 2: resolvconf set dns
$ sudo apt update
$ sudo apt install resolvconf