Linux

By the early 1990s, Stallman and a collection of other programmers working on GNU had developed a near-complete OS that could be freely shared. They were, however, missing a final essential piece in the form of a kernel� a complex system command processor that lies at the center of any OS. In 1991, Linus Torvalds wrote an early version of just such a kernel, released it under a free license, and called it Linux. Linus�s kernel was paired with the GNU project�s development tools and OS and with the graphical windowing system called X. With this pairing, a completely free OS was born�free both in terms of price and in Stallman�s terms of freedom.

All systems referred to as Linux today are, in fact, built on the work of this collaboration. Technically, the term Linux refers only to the kernel. Many programmers and contributors to GNU, including Stallman, argue emphatically that the full OS should be referred to as GNU/Linux in order to give credit not only to Linux but also to the GNU project and to highlight GNU�s goals of spreading software freedom�goals not necessarily shared by Linus Torvalds. Many others find this name cumbersome and prefer calling the system simply Linux. Yet others, such as those working on the Ubuntu project, attempt to avoid the controversy altogether by referring to GNU/Linux only by using their own project�s name.

Source of Information :  Prentice Hall The official Ubuntu Book 5th Edition 2010