I was handed a server with no docs and no idea what it was listening on. One command fixed that.

A client handed me SSH access to a server they'd been running for two years.

No documentation. No handoff notes. No "here's what's running and why." Just a root password in a LastPass share and a Slack message that said "it hosts our web app, let us know if you need anything."

I didn't know what the web app was. I didn't know what was installed. I didn't know what ports were open to the internet, what services were running, or what this machine had been doing quietly for 730 days before I touched it.

This is not unusual. This is actually most of the "inherited server" situations I've been in. The person who set it up is gone, or was a contractor, or was the founder who also did DevOps because someone had to, and the documentation lived entirely inside one person's head and left with them.

The first thing I do on an unfamiliar server is not grep logs or check running services. It's figure out what the machine is actually reachable on from the outside. Not what anyone says it's supposed to be doing. What it is doing. What ports are in LISTEN state, what process owns each one, and whether that process is bound to localhost or to every network interface on the machine.