Ask HN: What should a systems/low-level software engineer know?

Tired of the hype on the web/js (every week new library to learn about), I am thinking to switch career in the next 1-2 years, and move lower in the stack. I am into Rust in the last 3-4 months and I really enjoy it, but I would like to learn more, what would you consider essential books/papers/resources that a system's programmer should know?