This looks really cool. I have a pretty weak background in operating system fundamentals, and I always wanted to learn more about common system calls. I never realized the (2) on man pages meant it was for a system call specifically; I always treated the (2) or (3) on the man pages as if it was the first few entries in a really long stack trace (in other words, I barely even noticed it).
I was surprised to see that some of the exercises would require a newer kernel. I previously thought syscalls were a static unchanging interface to the kernel. But, indeed, statx (there are probably others I missed) was added to the Linux kernel just five years ago :)