xv6 is a pleasure to hack on and learn from! It's got everything you'd expect from a unix-like OS (multi-processor support, simple scheduler, unix-like FS, many

xv6 is a pleasure to hack on and learn from! It's got everything you'd expect from a unix-like OS (multi-processor support, simple scheduler, unix-like FS, many of the standard syscalls, fork/exec based shell, etc). Linux and *BSD may be the modern standard for unix-like OSes, but they're often too complex and opaque for beginners to learn from. It's super easy to read and toy with xv6's code if you want to learn more about OS internals, though. For example, I was able to implement a simple log structured file system: https://github.com/Jonanin/xv6-lfs https://github.com/Jonanin/xv6-lfs Note: if you're looking for companion reading material, check out this OS book: http://pages.cs.wisc.edu/~remzi/OSTEP/ http://pages.cs.wisc.edu/~remzi/OSTEP/ (IMO it's super approachable and understandable for undergrad-level learning)