(Shortcut) Uncomplicated Firewall on Ubuntu 20.04

ref https://www.cyberciti.biz/faq/unix-linux-check-if-port-is-in-use-command/ ref https://www.cyberciti.biz/faq/how-to-configure-firewall-with-ufw-on-ubuntu-20-04-lts/ sudo lsof -i:[port-number] sudo lsof -i -P -n | grep LISTEN sudo ufw status sudo ufw status numbered sudo ufw delete [number] sudo ufw enable sudo ufw disable sudo ufw allow 80/tcp comment 'accept Apache' sudo ufw allow 443/tcp comment 'accept HTTPS Connections' sudo ufw allow from [ip]