" It's not Linux, but MINIX can introduce you to the basic
concepts without all the baggage.
"Remember MINIX? Short for Minimal UNIX, MINIX is a close cousin
of GNU/Linux. To GNU/Linux users, it is simultaneously familiar and
foreign, and it challenges orthodox assumptions about how an
operating system should be designed.
"MINIX originally was developed in 1987 by Andrew S. Tanenbaum
as a teaching tool for his textbook Operating Systems Design and
Implementation. Today, it is a text-oriented operating system with
a kernel of less than 6,000 lines of code. MINIX's largest claim to
fame is as an example of a microkernel, in which each device driver
runs as an isolated user-mode process—a structure that not
only increases security but also reliability, because it means a
bug in a driver cannot bring down the entire system."