What Is Linux?

Linux is a clone of the Unix OS, which has been popular in academic and business environments for years. Linux consists of a kernel, which is the core control software, and many libraries and utilities that rely on the kernel to provide features with which users interact. The OS is available in many distributions, which are collections of a specific kernel with specific support programs. Popular Linux distributions include Arch, CentOS, Debian, Fedora, Gentoo, Mandriva, openSUSE, Red Hat, Slackware, SUSE Enterprise, and Ubuntu, but there are hundreds—if not thousands—of other Linux distributions. This book focuses on tools and techniques that are used in most, if not all, distributions, although from time to time it demonstrates some distribution-specific tools.

Linux has several characteristics that make it worth learning and using:

• Linux is open source software: the files used to create the working programs that make up Linux are freely available and may be modified and redistributed. If you dislike something about the way Linux works, you can change it yourself! (You may need modest-to-considerable programming skills to do so, however.)
• Linux is available free of charge. Although some distributions require payment, most can be downloaded from the Internet and used without paying a cent. This is a great boon for students, businesses on a shoestring budget, or anybody wanting to save money. Those who want to pay for greater support can do so by hiring consultants or by purchasing service contracts.
• As a clone of the older Unix OS, Linux has inherited a great deal of Unix software, including many important Internet server programs, databases, programming languages, and more.
• Linux is highly scalable—it runs on everything from mobile devices to supercomputers. The Linux versions described in the greatest detail in this book run on a more limited range of hardware, but they can run on systems that are several years old or on the very latest hardware. Linux can make good use of systems that are too old for the latest version of Windows or Mac OS X.
• Many businesses and nonprofit organizations rely on Linux. Although desktop systems still usually run Windows, Linux is often used to run the organizations’ websites, route their Internet traffic, and do other critical behind-the-scenes tasks. In some cases, Linux is used as the desktop OS too. Thus learning Linux will help your employment prospects.

You can install Linux on almost any system on which you normally run Windows or Mac OS X. You can install Linux by itself or side by side with another OS, so you can learn Linux without losing your ability to get work done in your regular OS.