My work in Linux is infrequent enough that I often forget the most basic things. Lucky once I get started the learning curve is pretty quick.
Something I always forget is how to add a firewall exception. In my experience if you're following an installation guide for an application, you get to the end of the guide, test it... Nothing. Then if you're lucky you remember the firewall.
firewall-cmd --permanent --add-service=http -add-service=https