My somewhat off-beat recommendation is "Lions' Commentary on UNIX 6th Edition with Source Code". The sources to a 1976 version of Unix written in an archaic dia

My somewhat off-beat recommendation is "Lions' Commentary on UNIX 6th Edition with Source Code". The sources to a 1976 version of Unix written in an archaic dialect of C and targeting a long-dead CPU architecture are obviously not of immediate relevance to the modern world, and may well not be to your taste unless you already have some sympathy with the idea of retrocomputing. But if you do: 6th Edition is small enough that you really can read through the whole set of sources and understand pretty much how the whole thing is put together; the basic bones of the design are not so far away from Linux, so it gives you a workable conceptual model of what the shape of the Linux sources are and what the various important parts are; the commentary is really good, explaining the inscrutable but nudging you to figure things out yourself too; and overall it is practice in reading a large volume of somebody else's code, which is something you're going to be doing all the time if you work on Linux or any modern kernel. You probably also want a more theoretical and general book too, of course.