During setting up PiHole, it requires to listen on DNS (53/TCP, 53/UDP) on the host. Ubuntu version that I am running on (20.04) by default listens on port 53 because it runs as DNS Stub Listener.
PiHole will give errors about Binding error
To disable Ubuntu running as DNS Stub Listener, do the followings:
> sudo vi /etc/systemd/resolved.conf
un-comment #DNSStubListener=yes
change it to DNSStubListener=no
> sudo service systemd-resolved restart
> sudo systemctl disable systemd-resolved.service
> sudo systemctl stop systemd-resolved
> sudo mv /etc/resolv.conf /etc/resolv.conf.old
> sudo shutdown -h now -r
