From the name I thought this was about learning NixOS, and they found a very clever name

Maybe the author could add a small note that this is not about that, and refer to something official about NixOS?

Anyway, I like the idea of the project!

This dedicates at least as much time to discussing the eccentricities of the underlying Rust implementation (and the Rust language itself) as it does to discussing the underlying low-level hardware/software concepts. Since this is very much still a work-in-progress (only the first three sections have been fully fleshed-out), I have a suggestion to make: please make it more language-agnostic, with a greater focus on the fundamentals versus the implementation.

Looking forward to going through the lessons

This is an ambitious project. Might I respectfully suggest that you use your favourite AI (or an English-speaking friend) to fix your many grammatical errors and typos? For example "Note: ALL the syntax highlighting of the Rust code is custom and create by me! If you see and bug, please write in the comments or submit an issue." should be "Note: ALL the syntax highlighting of the Rust code is custom and was created by me! If you see a bug, please leave a comment or submit an issue." Also, Rust, not rust. And many more.

Why always POSIX compliant? If its going to be a learning exercise or a hobby OS or just an exploration, why not throw POSIX out the window and start from scratch for designing the API?

I hope this builds on phil-opp's previous work which is IMO stellar.

I spotted at least 3 typos in the first minute. Typos are really easily detected and fixed with LLMs (one really good usage of them).

But it's nice to have non-LLM written text. Still the many typos are annoying and distracting.

I think it's really cool that they're using bare-metal Rust for this. It's a lot more accessible than C because the standard distribution (rustup) can work as a cross-compiler to a no-OS target out of the box. Deliberately avoiding dependencies makes me happy too, people really underestimate what you can do with Rust without relying on the whole dependency ecosystem, and this is better pedagogically because you can understand the whole system.

I'm rather amused at how https://www.learnix-os.com/ch01-02-booting-our-binary.html has you creating a 16-bit target that ostensibly uses 32-bit pointers in its data layout… presumably that doesn't actually work to compile normal code to, but I guess it works so long as it's just acting as a scaffold for inline assembly. It's cool they don't need to bring in a secondary toolchain for the 16-bit part of bootstrapping, even if I worry this might break in some future rustc/LLVM revision.