Set permanent DNS nameservers

To regain temporary internet access for package installation, open sudo nano /etc/resolv.conf and add a DNS server for example nameserver 8.8.8.8

Install the resolvconf package:

sudo apt install resolvconf

Enable and start the resolvconf service:

sudo systemctl enable resolvconf.service && sudo systemctl start resolvconf.service

Open resolv.conf using head file and enter your nameservers:

sudo nano /etc/resolvconf/resolv.conf.d/head

192.168.100.1 is my ISP default DNS/gateway address

Update resolv.conf nameservers:

sudo resolvconf -u

Open resolv.conf to confirm new nameservers have been written:

sudo nano /etc/resolv.conf

Can reboot to confirm it remains