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Linux- This article is about Linux-based operating systems, GNU/Linux, and related topics. See Linux kernel for the kernel itself. "Linux" is also the name of a German brand of washing powder.
 the penguin, the Linux mascot]]
Linux is the name of a computer operating system and its kernel. It is the most famous example of free software and of open-source development.
"Linux" strictly refers to the Linux kernel, but the name is commonly used to describe the entire Unix-like operating system (also known as GNU/Linux) formed by combining the Linux kernel with the GNU libraries and tools, and for whole Linux distributions, which typically also bundle large quantities of software, such as web servers, programming languages, databases, desktop environments like GNOME and KDE, and office suites like OpenOffice.org.
The kernel was originally developed for the 386 processor but now supports a vast range of architectures, and is deployed in applications ranging from personal computers to supercomputers and embedded systems such as mobile phoness and the TiVo PVR.
Initially developed and used mostly by individual enthusiasts, Linux has since gained the support of industry heavyweights such as IBM and Hewlett-Packard, overtaken many proprietary versions of Unix, and even challenged the dominance of Microsoft Windows in some areas. Analysts attribute this success to its low hardware cost and high speed compared to proprietary Unix, its security and reliability compared to Windows, and its low cost and vendor independence overall. Proponents attribute these traits to the open source development model.
History
See also: Timeline of Linux development
The Linux kernel was initially written as a hobby by Finnish university student Linus Torvalds, who was attending the University of Helsinki, as a free and modifiable Minix-like kernel. (Minix is a Unix-like teaching project designed for simplicity rather than production use.) Version 0.01 of Linux was released to the Internet in September 1991, 0.02 on October 5, 1991 [1]. Subsequently, thousands of volunteer developers throughout the world have participated in the project. The essay The Cathedral and the Bazaar discusses the development model of the Linux kernel and similar software.
The history of Linux is closely tied to that of the GNU project, a prominent free-software project led by Richard Stallman. The GNU project was begun in 1983 to develop a complete Unix-like operating system — compilers, application programs, development utilities and so on — composed entirely of free software. By 1991, when the first version of the Linux kernel was written, the GNU project had produced nearly all of the components of this system — except the kernel. Torvalds and other early Linux-kernel developers adapted their kernel to work with the GNU components to create a fully functional operating system. The Linux kernel thus filled the last major gap in the GNU project. (Note that the Linux kernel is not part of the GNU project, although it is now licensed under the GNU General Public License.)
Tux the penguin is the logo and mascot of Linux. The Linux trademark (SN: 1916230) is owned by Linus Torvalds, registered for "Computer operating system software to facilitate computer use and operation." The assignment of the trademark to Torvalds occurred after an attorney, one William R. Della Croce, Jr, in 1996 began sending letters to various Linux distributors claiming to own the "Linux" trademark and demanding 10% royalties. The distributors rapidly pooled resources, appealed against the original trademark assignment and had it reassigned to Linus Torvalds. The licensing of the trademark is now handled by the Linux Mark Institute.
Pronunciation of "Linux"
According to Torvalds, "Linux" is pronounced to rhyme with "Minix" [1]:
- "Li" is pronounced with a short [ee] sound: compare prInt, mInImal etc. 'nux' is also short, non-diphtong [sic], like in pUt. It's partly due to minix: linux was just my working name for the thing, and as I wrote it to replace minix on my system, the result is what it is ... linus' minix became linux.
An audio file of Torvalds saying "Hello, this is Linus Torvalds, and I pronounce Linux as Linux" also exists [1]. Note that in English, "Linux" and "Minix" are often pronounced with a short I sound that is different from Torvalds' Finland-Swedish pronunciation of these words.
See also List of words of disputed pronunciation#Names for a discussion of the various ways "Linux" is pronounced.
"GNU/Linux"
Main article: GNU/Linux naming controversy
Because GNU — without which the system would not resemble Unix — stems from a long-standing and well-integrated free operating system project that predates the Linux kernel itself, Richard Stallman and the Free Software Foundation ask that the combined system (regardless of distribution) be referred to as "GNU/Linux." Some people do — notably the Debian project — although most simply call the system "Linux."
The distinction between Torvalds' kernel and entire Linux-based operating system distributions (of which the kernel forms only a small part) is a perennial source of confusion, and the naming remains controversial.
Litigation
Main article: SCO v. IBM
In March 2003, the SCO Group (SCOG) filed a lawsuit against IBM claiming that IBM had contributed portions of SCOG's intellectual property into the Linux kernel in violation of IBM's license to use UNIX, now claimed to be held by SCOG. Additionally, SCOG sent letters to a number of companies warning them that their use of Linux without a license from SCOG may be actionable, and have claimed in the press that they would be suing individual Linux users. This controversy has more recently involved lawsuits by SCOG against Novell, DaimlerChrysler, and AutoZone, as well as by Red Hat and others against SCOG.
Linux distributions
Main article: Linux distribution
Linux is almost always used as part of a Linux distribution (distro). These are assembled by individuals, corporations, countries, and other organizations, and each may include any number of additional system software and application programs, as well as a program to install the whole system on a new computer. Distributions are created for many different purposes, including localization, architecture support, real-time applications, and embedded systems, and there are many which deliberately include only free software.
A typical general-purpose distribution includes the Linux kernel, the GNU libraries and tools, command-line shellss and also offers a tremendous amount of application software, from office suites and the graphical X Window System to compilers, text editors, and scientific tools.
Scale of development efforts
More Than a Gigabuck: Estimating GNU/Linux's Size, a study of Red Hat Linux 7.1, found that this particular distribution contained 30 million physical source lines of code (SLOC). Using the COCOMO cost model, the study estimated that this distribution required about 8,000 person-years of development time. Had all this software been developed by conventional proprietary means, it would have cost over $1.08 billion ($1,080 million), in year 2000 dollars, to develop in the US.
The majority of the code (71%) was in C, but many other languages were used, including C++, shell scripts, Lisp, assembly language, Perl, Fortran and Python. Slightly over half of all its code (counting by line) was licensed under the GPL. The Linux kernel contained 2.4 million lines of code, or 8% of the total — the vast majority of a Linux distribution consists of code that is not contained in the Linux kernel.
A later study (Counting potatoes: the size of Debian 2.2) performed the same analysis for Debian GNU/Linux version 2.2 (aka "Potato"). This distribution contained over 55,000,000 physical SLOC, and would have taken $1.9 billion USD (year 2000 dollars) to develop by conventional proprietary means.
Applications of Linux-based operating systems
In the past, a Linux user needed significant knowledge of computers in order to install and configure his system. For this reason and, 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 increasing user-friendliness and broader adoption of many Linux distributions. Linux has made considerable progress in the server and special-purpose markets (e.g. image rendering and Web services), and is beginning to make inroads into the high volume "desktop" market.
Linux is the cornerstone of the LAMP server-software combination (Linux, Apache, MySQL, Perl/PHP/Python) that has achieved widespread popularity among web developers.
Linux is also commonly used as an embedded system. Its low cost makes it ideal for such devices as the Simputer, a low-cost computer aimed especially at low-income populations in developing nations.
With desktop environments such as KDE and GNOME, Linux offers a user interface like that of the Apple Macintosh or Microsoft Windows in addition to its traditional Unix-like command line interface. Graphical Linux software exists for many niches, although in many areas there is still greater breadth and quantity of proprietary software.
Usability, market share and moving from Windows
Once viewed as an operating system only computer geeks could use, Linux is today a much more user-friendly system, with many graphical interfaces and applications that bear a close resemblance to those of popular consumer operating systems.
Its market share for desktop usage remains small but growing. According to market research company IDC, the 2002 Linux market share was 25% for servers and 2.8% for personal/desktop computers. 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. In these cases, only a few applications have typically been required and administration may be handled by a small number of skilled IT staff.
Linux and other free software projects are frequently criticised for not going far enough in terms of ensuring usability, and the question of Linux's usability compared to Windows or the Macintosh remains hotly debated. For those only familiar with Windows or the Macintosh, using Linux may be difficult because many things do not work identically, and substantial differences remain in more sophisticated administrative and configuration tasks. It is also usually easier to find local technical support for Windows or MacOS than for Linux.
Additionally, users will often have to switch application software as well, and equivalents of some programs may not be available (or there may be less selection, e.g. with games). However, more office and home applications now come with an installation. Because of reluctance to change operating systems, or even upgrade from one version of the same system to the next, and the fact that most computers come with Windows pre-installed, there is a slow adoption of new desktop operating systems.
There have been conflicting studies of Linux's usability and cost. Relevantive, a Berlin-based company specializing in consulting companies on the usability of software and Web services, concluded in 2003 that the usability of Linux for a set of specific desktop-related tasks was "nearly equal to Windows XP." On the other hand, Microsoft-sponsored studies by IDC have argued that Linux has a higher total cost of ownership (TCO) than Windows.
Linux has been criticized for unpredictable development schedules, thus making enterprise users less comfortable with Linux than they might be with another operating system (Marcinkowski, 2003). The large number of choices in Linux distributions has also been argued to confuse consumers and software vendors. On the other hand, Linux supporters have pointed out that Microsoft release dates also have a reputation for slipping.
The paper Why Open Source Software / Free Software (OSS/FS)? Look at the Numbers! identifies many quantitative studies of open source software, including market share, reliability, and so on, with many studies specifically examining Linux.
Several projects attempt to make Windows applications runnable on Linux, with varying degrees of success. VMware and Win4Lin run Windows applications in an emulator, with perfect functionality but a severe speed penalty. WINE (and its commercial packaging, CrossOver Office) use a compatibility layer, allowing native speed but only for certain applications.
Installation
Difficulty of installation was initially a high barrier to adoption, but the installation process has been greatly eased in recent years, some distributions being easier to install than comparable versions of Windows.
With the adoption of Linux by several large PC manufacturers, computers with Linux distributions pre-installed have become available.
Distributions increasingly allow Linux to be booted directly from a live CD without modifying the hard drive. CD ISO images for these and other distributions can usually be downloaded from the Internet, burneded to a CD and booted from the CD.
Linux can also be booted over a network or, for a minimal system, from a few floppy disks or network card NetBoot flash drivers (see Isolinux).
Configuration
Configuration of most settings is stored in a directory called /etc, while others store settings in hidden files in the user's home directory. Some programs use a configuration database instead of files.
There are a number of ways to change these settings. The most common way to do this is using tools provided by distributions such as SuSE's YaST or Mandrake's Control Center. There are non-distribution-specific utilities such as Linuxconf and the GNOME System Tools. There are also many command line utilities for configuring programs. Finally, since most settings are stored in text files they can be configured by any text editor.
Support
Support is generally provided by peers — other Linux users, usually online, in forums, newsgroups and mailing lists. Linux User Groups (LUGs) have sprung up all over the world as a way of assisting local users, new and experienced alike, with the installation, use, maintenance and advocacy of Linux systems.
Commercial suppliers of Linux distributions generally have a business model of providing support. Third-party support is also readily available.
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