This is a minimal example of a working Linux distribution, aka "micro distribution". It has two flavors:
hello_world: Uselessinit, just prints something to the console.little_shell: A slightly less uselessinit. It spawns another process which handles user input and output.
You can make the initramfs.cpio from both of these directories (make sure to override the make flag for cross compile to match your platform).
This repo is meant to accompany the article at http://popovicu.com/posts/making-a-micro-linux-distro