Now would be a good time for a quick refresher of the Linux boot process. When you turn on your Linux-based system, the kernel image (stored in a single binary file) is loaded from disk to memory by a boot loader, such as LILO or GRUB. At this point, the kernel takes control of your system. One of the first things it does is detect and initialize all the hardware that it finds and has been configured to support. Once the hardware has been initialized properly, the kernel is ready to start normal user-space programs (also known as "processes").

The first process run by the kernel is /sbin/init. It, in turn, starts additional processes as specified in /etc/inittab. Within seconds, your Linux system is up and running, ready for you to use. Although you never interact with the kernel directly, the Linux kernel is always running "above" all normal processes, providing the necessary virtualization and abstractions that your various programs and libraries require to function.