I want to play with Linux to better understand how it works. Thus, I am looking for a very basic and small Linux to play with. I tried small Linux distributions (which copy themselves to RAM), but they have their own structure (like Live CD). Instead, I wish to have a minimal but standard Linux structure.
I installed minimal version of Debian on USB and setup GRUB to separate this experiment from my main computer. However, Debian (even minimal) is far more advanced than what I need.
What is the best method to copy a very minimal version of Linux on USB and boot with GRUB? Each distribution has its own features and options, but I prefer to be closer to the standard Linux (Linux kernel) without customization of a distribution.