Let’s start with a quick overview: Linux is a computer operating system, like Microsoft
Windows, Mac OS X, and Unix. In fact, Linux is a clone of Unix. Unix is the venerable, battle-tested operating system that has powered the world’s servers—from mainframes down to small department servers—since the early 1970s.
There are many different variants of Unix. Some are open source and free of cost, such as FreeBSD and OpenBSD, and some are closed-source commercial systems such as IBM’s AIX and Hewlett-Packard’s HP-UX. Apple’s Mac OS X is a certified Unix variant, while Linux is a non-certified Unix-like operating system.