Lots of comments so far about using Linux From Scratch to learn about the userspace/kernelspace interaction, and while that's all feasible you can do this on basically any distro.
This week I've been iteratively rebuilding the kernel and glibc and the vDSO on my Ubuntu Server 20.04 install and learning a ton about the interactions, while also having the Ubuntu apt repositories to fall back on for when I want to switch from "learning mode" to "just get this task done mode."
This week I've been iteratively rebuilding the kernel and glibc and the vDSO on my Ubuntu Server 20.04 install and learning a ton about the interactions, while also having the Ubuntu apt repositories to fall back on for when I want to switch from "learning mode" to "just get this task done mode."