Pick an operating system, e.g. Haiku(BeOS), Plan9, Net/Open/Free-BSD. Download the source code and dig in. Read the source, the comments, commit logs and email

Pick an operating system, e.g. Haiku(BeOS), Plan9, Net/Open/Free-BSD. Download the source code and dig in. Read the source, the comments, commit logs and email threads. IMO Linux has gotten too big and complex due to having to support so many processors and devices. Most existing systems programming is in C/C++. Rust is new and there isn't much battle hardened code out there.