About Linux

What is Linux?

Linux is a UNIX-like kernel, which is written by Linus Torvalds and other developers. Linux runs on many different architectures, for example on IA32, IA64, Alpha, m68k, SPARC and PowerPC machines. The latest kernel and information about the Linux kernel can be found on the Linux kernel website: http://www.kernel.org

The Linux kernel is often confused with the GNU/Linux operating system. Linux is only a kernel,not a complete operating system. GNU/Linux consists of the GNU operating system with the Linux kernel. The following section gives a more extensive description of GNU/Linux.

What is GNU/Linux?

In 1984 Richard Stallman started an ambitious project with the goal to write a free UNIX-like operating system. The name of this system is GNU, which is an acronym of “GNU’s Not UNIX”. Around 1990, all major components of the GNU operating system were written, except the kernel. Two years earlier, in 1988, it was decided that the GNU project would use the Mach 3.0 microkernel as the foundation of its kernel. However, it took until 1991 for Mach 3.0 to be released under a free software license. In the the same year Linus Torvalds started to fill the kernel gap in the GNU system by writing the Linux kernel. GNU/Linux thus refers to a GNU system running with the GNU/Linux kernel. The GNU kernel, named “HURD” was still under development when this book was written, and is available as the GNU/HURD operating system. There are some other kernels that are ported to the GNU operating system as well. For instance, the Debian project has developed a version of the GNU operating system that works with the NetBSD kernel.

The UNIX philosophy

Since GNU/Linux is a free reimplementation of the UNIX operating system, it is a good idea to look at the philosophy that made UNIX widely loved. Doug McIlroy summarized the UNIX philosophy in three simple rules:

• Write programs that do one thing and do it well.
• Write programs to work together.
• Write programs to handle text streams, because that is a universal interface.

Odds are that you do not intend to write programs for GNU/Linux. However, even as a user these basic UNIX rules can mean a lot to you. Once you get to know the essential commands that have been part of UNIX for many years, you will be able to combine simple programs to solve complex problems. Keep this in mind while you learn Slackware Linux; try to get a feeling for how you can divide complex tasks in simple combined operations.

Free and open source software

Most packages in Slackware Linux are published under a free software or open source license.
Under these licenses software may be used, studied, changed and distributed freely. Practically,this means that the software is available and redistributable in source and binary form. Although the free software and open source software movements share many licenses and principles, there are subtle differences between both movements. The open source movement tends to focus on the economic and technical advantages of sharing source code, while the free software movement puts accent on the ethical side of providing sources and binaries freely. As the GNU website puts it: “Free software is a matter of liberty, not price. To understand the concept, you should think of free as in free speech,not as in free beer. 1” In the spirit of free and open source software the source code of almost all packages is included on the third and fourth CDs in the Slackware Linux CD set.