Are there good resources for a new systems programmer to learn about Linux? Everything I know of is either: academic textbook which is too abstract to learn about the details, docs or LKML which assume the reader has a lot of context, or aimed at users rather than devs

Example questions to clarify level: what are pros and cons of memmap? What are the different ways to request memory from the kernel? How does linking work? What’s the security model in a modern Linux version?