The following is Richard Stallman's answer to the question, “What is Linux?” . . .

> Some people say “Linux is what Linus says it is”, but I'm not
> satisfied with that.

Linus Torvalds is entitled to choose the name for the kernel whose development he launched; since he says that kernel is Linux, it is Linux. Unless you are trying to be disrespectful, you shouldn't call it anything but Linux.

The complete operating system which is commonly used on servers and PCs is basically the GNU system, with Linux added as the kernel. Since it is the combination of GNU and Linux, GNU/Linux is an appropriate name for it. (The slash means combination, as in “I/O”.)

The principal API of this system does not come from Linux, since user programs do not communicate directly with the kernel. It comes from the GNU C library, which is a part of the GNU system.

It's hard for users to learn the difference between the kernel and the whole system if people call them both by the same name. Many users are confused. This confusion leads often to erroneous conclusions such as “The Linux operating system is released under the GNU GPL”. In fact Linux, the kernel, is released under the GNU GPL, but there is no single license for the whole operating system: many programs are under the GNU GPL, but some have other licenses.

By distinguishing consistently between Linux and GNU/Linux, you can help straighten out the confusion between the kernel and the whole system. (See www.tux.org/lkml/index.html#s1-1.) You can also give the system's principal developer, the GNU Project, a share of the credit for its work. We started developing this system in 1984, many years before Linux was begun–and the name we gave it is “GNU”.

> . . . If a proprietary RTOS like LynxOS or QNX attains plug-and-play
> binary (API/ABI) compatibility with Linux apps, is it Linux?

A Linux-compatible kernel is not Linux, any more than a Unix-compatible operating system such as GNU is Unix. (Remember, GNU's *Not* Unix.)

(Is this really a matter of compatibility with Linux, or with the GNU C library?)

 
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