In my first job out of college was supporting monitoring software in big financials. They often didn't even know what they were running. More than once got sat

In my first job out of college was supporting monitoring software in big financials. They often didn't even know what they were running. More than once got sat down and told to connect to their HP-UX, AIX, Solaris, Linux, etc box and setup things up. Would have to go back and explain that particular server was actually something different and I'd put the appropriate build on it. Of course, every system had to have it's own build, and own scripts to accommodate all the differences mentioned here. University CS courses had definitely not covered things like GNU vs BSD tools, and various other differences. I remember being advised early on in that job to learn vi, not because it's the best editor, but just because it's the only one you can rely on being everywhere, on every server. There were other discussions in the office about which editor for actual dev work, but for client visits on random servers - vi is always there.