In some ways, the boot process is surprisingly simple. The kernel starts up single-threaded and synchronous on a single core and seems almost comprehensible to the pitiful human mind. But how does the kernel itself get started? What functions do initrd [initial ramdisk] and bootloaders perform?

Abstract:

define how the system boots up starting from the post through initramfs ( why, when, how it works ), , at what time selinux comes into the picture, how the kernel is pivoted on the actual filesystem.

1. The beginning of boot
2. Provisioning a booting kernel
3. From start_kernel function to PID 1