Linux is a computer operating system and its kernel. It is one of the most prominent examples of free software and of open-source development: unlike proprietary operating systems such as Windows and Mac OS, all of its underlying source code is available to the public and anyone can freely use, modify, and redistribute it.
In the narrowest sense, the term Linux refers to the Linux kernel, but it is commonly used to describe entire Unix-like operating systems (also known as GNU/Linux) that are based on the Linux kernel combined with libraries and tools from the GNU project and other sources. Most broadly, a Linux distribution bundles large quantities of application software with the core system, and provides more user-friendly installation and upgrades.
Initially, Linux was primarily developed and used by individual enthusiasts. Since then, Linux has gained the support of major corporations such as IBM, Hewlett-Packard, and Novell for use in servers and is gaining popularity in the desktop market. Proponents and analysts attribute this success to its vendor independence, low cost, security, and reliability.
Linux is predominantly used as part of a Linux distribution (distro). These are compiled by individuals, loose-knit teams, and various professional organizations. They include additional system software and application programs, as well as certain processes to install these systems on a computer. Distributions are created for many different purposes, including localization, architecture support, real-time applications, and embedded systems, and many deliberately include only free software. Over 450 distributions are available .
A typical general-purpose distribution includes the Linux kernel, some GNU libraries and tools, command-line shells, and thousands of application software packages, from office suites and the graphical X Window System to compilers, text editors, and scientific tools. A variety of Linux distribution screenshots can be viewed here.
In the past, a user needed significant knowledge of computers in order to install and configure Linux. Because of this, and because of being attracted by access to the internals of the system, Linux users have traditionally tended to be more technologically oriented than users of Microsoft Windows and Mac OS, often revelling in the tag of "hacker" or "geek."
This stereotype has been dispelled in recent years by the increased user-friendliness and broad adoption of many Linux distributions. Linux has made considerable gains in server and special-purpose markets, such as image rendering and Web services, and is now making inroads into the high volume desktop market.
Its market share of desktops is rapidly growing. According to market research company IDC, in 2002, 25% of servers and 2.8% of desktop computers were already running Linux. However, argued advantages of Linux, such as lower cost, fewer security vulnerabilities, and lack of vendor lock-in, have spurred a growing number of high-profile cases of mass adoption of Linux by corporations and governments. The Linux market is among the fastest growing and is projected to exceed $35.7 billion by 2008 .
Linux and other free software projects have been frequently criticized for not going far enough in terms of ensuring usability, and Linux has been generally considered more difficult to use than Windows or the Macintosh, although it is steadily improving. Applications running within graphical desktop environments such as GNOME and KDE in Linux are very similar to those running on other operating systems. While some applications cannot be run, there usually exists a replacement that will. A growing number of proprietary software vendors are supporting Linux, and open source development for Linux is also steadily increasing. Additionally, proprietary software for other operating systems may be run through compatibility layers, such as Wine.