Set up the firewall

It is a good idea to block incoming requests on all but trusted ports.

Be careful, it is possible to block your own SSH access to the server!

Some common ports:

• 22: SSH
• 80: HTTP
• 443: HTTPS
• 1965: Gemini
• 5222: XMPP client
• 5269: XMPP server-to-server connections
• 8448: Matrix federation

apt install ufw
ufw default deny incoming
ufw default allow outgoing
ufw allow 22
ufw allow 80
ufw allow 443
ufw allow 1965
ufw show added
ufw enable