Which tasks to learn and which books to read to become more skilled at Unix/Linux internals?

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http://unix.stackexchange.com – I recently interviewed at a major company and did well on programming questions ("What is the time complexity of quicksort? What is the opposite in C of malloc? What is the opposite in C++ of new? What is the first argument in a Python function?") but I couldn't answer many of the networking / operating system questions so I wonder how to fill this gap. I plan to read the book "Operating Systems" by tanenbaum and I wonder even though SO is not a recommendation engine in this case if you can tell my other pointers or concrete recommendation how to practice linux/unix internals besides using a l (HowTos)