Without an operating system, the hardware of your computer would do nothing. The operating system is made up of many small programs that work together. Every operating system has a core component, which starts up all the other components and controls the activities of the computer. This component is known as the kernel.

Shells, terminals, and the kernel
The kernel is simply a file, usually called vmlinuz which is located on the hard drive and loaded when you first boot your computer. When you work with the system, you are interacting with the kernel. This interaction cannot happen directly. There must be an interface between you and the kernel.

The basic interface is called a terminal. Once you log into a terminal, you receive a user interface called a shell, which accepts your commands.

The shell that is used by default in Linux is the BASH shell (Bourne Again shell), which is an improved version of the Bourne Shell developed by AT&T for UNIX. BASH is the shell we will be using.

Because Linux is a multi-user OS, there can be many terminals active at the same time, allowing you and other users to operate the system. The four different terminals shown in Exhibit 3-1 could each be a different user or four separate terminals supporting tasks run by a single user. Because Linux is designed to work over networks, one user could be seated at the server itself and the other three could be logged in across the local network, or over the Internet.
A Linux system can be operated entirely by text-based terminals, using command line programs. A typical command-line terminal login prompt looks like this:

Fedora Core release 2 (Tettnang) Kernel 2.6.5-1.358 on an i686