Troubleshooting Problems with Postfix, Dovecot, and MySQL

https://www.linode.com/docs/email/postfix/troubleshooting-problems-with-postfix-dovecot-and-mysql/

How to Setup an Ubuntu Linux VM in Azure with Remote Desktop (RDP) Access

How to install Certbot plugins?

First run

To find out where certbot is installed to. Or command -v certbot if you prefer.

Then run head /usr/bin/certbot and note what version of Python it’s using:

In my case, it was using Python 3.

I noticed from my pip output it was trying to install a Python 2.7 package:

So how do we get pip to install Python 3 packages instead? Just copy the instructions from here:

Now you should have the pip3 command, so run this instead:

And now try again:

Running multiple OpenVPN instances (multi port)

https://www.hugeserver.com/kb/openvpn-multiple-ports/

Automatically renew Letsencrypt certificate with Certbot

https://certbot.eff.org/lets-encrypt/ubuntuxenial-apache

Generate wildcard certificate

An In-Depth Guide to iptables, the Linux Firewall

This is a great guide to iptables:

An In-Depth Guide to iptables, the Linux Firewall

The Beginner’s Guide to iptables, the Linux Firewall

https://www.howtogeek.com/177621/the-beginners-guide-to-iptables-the-linux-firewall/