A very good introduction to UNIX system fundamentals, a classic system engineer textbook. Providing a lot of background with easy hands-on code examples.
Best part, the book is extremely practical, while also explaining many variations among unix, linux and macos.
Recommended in here: http://coolshell.cn/articles/4990.html
Finished the book with various chapters in the second half skipped. They are mostly about highly specific system level features which I don’t think urgent to learn.