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

Linux is many things. It's an operating systems kernel. It's a distribution. It's a community. It's a movement. Today, I feel that using the word “Linux” refers to the general community-based developmental movement forward of anything that runs on or is associated with a Linux kernel.

Technically, I suppose you could say that Linux is anything that Linus Torvalds releases as Linux on www.kernel.org. But, nowadays, Linux is the name of several major distributions of kernels and many associated free tools, mostly from GNU. So anything that is released under these distributions could be reasonably called Linux. So Red Hat, Debian, Caldera, MontaVista, and others now get more of a say in what is “Linux.”

Of course, there are many, many people working on enhancements to the Linux kernel and programs that will run on it. Some of these people make changes to the kernel, and release their changes to the public, not available through any other distribution. These kernels are Linux, although they may be “Linux-temporary,” depending on whether they ever get merged into a kernel.org tree, or a tree from a major distribution provider. The Linux community is a democracy and is very much driven by usefulness, and some people manage to produce enhancements that are quickly used by many. These creators find themselves automatically (autocratically?) picked up by the community and their enhancements and positions become “Linux.”

So, there are various levels and degrees by which something or somebody attains or is associated with Linux. All of Linux, however, shares a common history: the kernel and many of it's applications provided on the distributions are enhancements and changes to something that existed in a previous distribution. So, although Linux has a defined API and ABI (still changing), a kernel or RTOS that emulated this API/ABI wouldn't be Linux, it would be Linux-like, since it doesn't have it's roots with Linux. There are many examples of this emulation in software, such as the Wine Project. However great, they remain emulations of the Real Thing. Because they're not attached to the growing tree of Linux, they must always be kept up after-the-fact, and can't attain the following Linux has. And why should they? With the entire Linux source open, an RTOS vendor that built a Linux-like system rather than just using Linux is obviously prioritized around their own operating system, and this goes against the Linux movement!

Linux is certainly a technology, and a rapidly customizable one. Linux's greatest asset is the number of people it's been able to attract, and most these people are developmentally oriented. What a way to produce software!

 
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