A: The name "Linux" is used to refer to three similar yet slightly different things, which can be confusing to all but the hardcore geek. The three usages vary by how much of a complete software system the speaker is talking about.

At the lowest level, every Linux system is based on the Linux kernel the very low-level software that manages your computer hardware, multi-tasks the many programs that are running at any given time, and other such essential things. These low-level functions are used by other programs, so their authors can focus on the specific functionality they want to provide. Without the kernel, your computer is a very expensive doorstop. It has all of the features of a modern operating system: true multitasking, threads, virtual memory, shared libraries, demand loading, shared, copy-on-write executables, proper memory management, loadable device driver modules, video frame buffering, and TCP/IP networking.

Most often, the name "Linux" is used to refer to the Linux Operating System. An OS includes the kernel, but also adds various utilities the kinds of programs you need to get anything done. For example, it includes a shell (the program that provides a command prompt and lets you run programs), a program to copy files, a program to delete files, and many other odds and ends. Some people honor the request of Richard Stallman and the GNU Project, and call the Linux OS GNU/Linux, because a good number of these utility programs were written by the GNU folks.

Finally, software companies (and sometimes volunteer groups) add on lots of extra software, like the XFree86 X Window System, Gnome, KDE, games and many other applications. These software compilations which are based on the Linux OS are called Linux distributions.

So, there are three Linuxes: the Linux kernel, the Linux OS, and the various Linux distributions. Most people, however, refer to the operating system kernel, system software, and application software, collectively, as "Linux", and that convention is used in this FAQ as well.

See also the Wikipedia articles on the Linux kernel and the Linux operating system.

A: Officially an operating system is not allowed to be called a Unix until it passes the Open Group's certification tests, and supports the necessary API's. Nobody has yet stepped forward to pay the large fees that certification involves, so we're not allowed to call it Unix. Certification really doesn't mean very much anyway. Very few of the commercial operating systems have passed the Open Group tests.

A: Unofficially, Linux is very similar to the operating systems which are known as Unix, and for many purposes they are equivalent. Linux the kernel is an operating system kernel that behaves and performs similarly to the famous Unix operating system from AT&T Bell Labs. Linux is often called a "Unix-like" operating system. For more information, see http://www.unix-systems.org/what_is_unix.html.

[Bob Friesenhahn]

A: Linus Torvalds and a loosely knit team of volunteer hackers from across the Internet wrote (and still are writing) Linux from scratch.

A: Linus has placed the Linux kernel under the GNU General Public License, which basically means that you may freely copy, change, and distribute it, but you may not impose any restrictions on further distribution, and you must make the source code available.

This is not the same as Public Domain. See the Copyright FAQ, ftp://rtfm.mit.edu/pub/usenet/news.answers/law/copyright, for details.

Full details are in the file COPYING in the Linux kernel sources (probably in /usr/src/linux on your system). There is a FAQ for the GPL at: http://www.gnu.org/copyleft/gpl-faq.html.

The licenses of the utilities and programs which come with the installations vary. Much of the code is from the GNU Project at the Free Software Foundation, and is also under the GPL. Some other major programs often included in Linux distributions are under a BSD license and other similar licenses.

Note that discussion about the merits or otherwise of the GPL should be posted to the news group gnu.misc.discuss, and not to the news:comp.os.linux hierarchy.

For legal questions, refer to the answer: Where Are Linux Legal Issues Discussed?.

A: This question produces an outrageous amount of heated debate.

If you want to hear Linus himself say how he pronounces it, download english.au or swedish.au from ftp://ftp.funet.fi/pub/Linux/PEOPLE/Linus/SillySounds/. If you have a sound card or the PC-speaker audio driver you can hear them by typing

$ cat english.au >/dev/audio

The difference isn't in the pronunciation of Linux but in the language Linus uses to say, "hello".

For the benefit of those who don't have the equipment or inclination: Linus pronounces Linux approximately as Leenus, where the ee is pronounced as in "feet," but rather shorter, and the u is like a much shorter version of the French eu sound in peur (pronouncing it as the u in "put" is probably passable).

A: Linux is freely available, and no one is required to register with any central authority, so it is difficult to know. Several businesses survive solely on selling and supporting Linux. Linux newsgroups are some of the most heavily read on Usenet. Accurate numbers are hard to come by, but the number is almost certainly in the millions.

However, people can register as Linux users at the Linux Counter project, which has been in existence since 1993. In May of 2003 the project counted more than 134,000 users, but that is certainly only a small fraction of all users. The operator of the Linux Counter estimated 18 million users, as of May 2003.

Visit the Web site at http://counter.li.org/ and fill in the registration form.

The current count is posted monthly to news:comp.os.linux.misc, and is always available from the Web site.

[Harald Tveit Alvestrand]

A: In 1999, International Data Corporation released its first commercial forecast of Linux sales. The report quantifies Linux vendor sales in 1996, 1997, and 1998, and forecasts through the year 2003.

To obtain the report, contact IDC at ctoffel@idc.com. Their Web site is http://www.itresearch.com/.