Aug 27, 2019

Zhao Jiong released this excellent work in English not too long ago: http://www.oldlinux.org/download/ECLK-5.0-WithCover.pdf If you know Chinese it was originally done in that language, details are on http://www.oldlinux.org/ It heavily comments / explains everything in the linux kernel v0.12. Quite some time ago, but I agree with the assessment on its relevance for an "inductive understanding". The growth since then is largely in new subsystems, new drivers, but maybe not so much in core theory...

If you're more into the core theory and less about Linux in particular, a fun project-oriented approach to get more familiar with the basics would be to get a little development board for an ARM CPU and try to make a multi-tasking (real-time) OS for it from scratch.