One of my favorite interview questions: "Here are some SSH credentials. What does this system do?"

Sometimes there aren't any docs. Sometimes the docs are wrong. It's important to be able to establish what the actual running situation is.

When I was interviewing people on behalf of a client, I was surprised at the number of people who didn't even know what SSH was. This was for a mid-level software developer and not a junior and they all came with glowing resumes.

They all insisted that it was essential to have a CI/CD process but didn't even know what the "CD" part even did. Apparently you just "git push" and the code magically gets on the server. There are many ways to do deployments and a CI/CD process isn't always suitable and can have many forms, in my opinion, but I was happy to discuss any and all. But it's difficult to do that without the basics. As you said, before I was commissioned the platform had no documentation, was crumbling under tech debt and failing constantly so something like getting on the server to at least figure out what's going on was essential.

  # ip a
  # ss -tulpn
  # ps aux
  # df -h
  # apt install lnav
  # journalctl -f | lnav

Mind you, my job title is MD, so I get that luxury.

Gathering and mapping unfamiliar systems is part of that skillset. I’m also looking at being able to think laterally, being able descend abstraction layers, and understanding architectural characteristics and constraints (Roy Fielding’s Dissertation), which will recur at each level of abstraction.