Ask HN: Fundamental texts for serious web engineers?

As someone who would like to be a one-man-army / technical co-founder in the world of web development, I've been recently trying to deepen my technical knowledge of the fundamentals. I realized my understanding of the basics was very simplistic and as far away from "hardcore" as imaginable. I spent years working in the industry, and made the giant early mistake of not asking "how does this actually work underneath?" for way too long, so now I'm embarking on the likely life-long journey to fix that.

I realize that it's impossible to gain truly deep knowledge into every aspect of web engineering, but I believe that given time one can still be proficient in most of its areas. More importantly, this knowledge should be abstracted from the "flavor of the month" technology, and it should enable one to quickly learn and adapt. Also I think this knowledge should be pragmatic, practical and highly relevant to the real world and business application.

For starters I began learning more about how programming languages work underneath, which so far Programming Language Pragmatics 3rd ed has been really good at explaining, at just the right level of detail.

I imagine that some of the other fundamental areas of understanding for a web developer would be:

- operating systems - networking - databases - security - distributed systems - UX

For these areas, and more if you can identify them, would you folks be able to recommend modern and pragmatic texts that would give one a solid level of depth? I realize that there would be plenty of overlap with a standard CS curriculum, the difference would be in a higher focus on practical application, rather than theory.