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This article is about operating systems that use the Linux kernel. For the kernel itself, see
Linux kernel. For other uses, see Linux (disambiguation).
Tux, the penguin, mascot of the Linux kernel
OS family Unix-like
Kernel type Monolithic kernel
GNU General Public License and
Working state Current
Linux (commonly pronounced IPA: /ˈlɪnəks/ in English; variants exist) is a Unix-like
computer operating system. Linux is one of the most prominent examples of free
software and open source development: typically all underlying source code can be freely
modified, used, and redistributed by anyone.
The name "Linux" comes from the Linux kernel, started in 1991 by Linus Torvalds. The
system's utilities and libraries usually come from the GNU operating system, announced
in 1983 by Richard Stallman. The GNU contribution is the basis for the alternative name
Predominantly known for its use in servers, Linux is supported by corporations such as
Dell, Hewlett-Packard, IBM, Novell, Oracle Corporation, Red Hat, and Sun
Microsystems. It is used as an operating system for a wide variety of computer hardware,
including desktop computers, supercomputers, video game systems, such as the
PlayStation 2 and PlayStation 3, several arcade games, and embedded devices such as
mobile phones, routers, and stage lighting systems.
• 1 History
o 1.1 MINIX
o 1.2 Commercial and popular uptake
• 2 Design
o 2.1 User interface
• 3 Development
o 3.1 Community
o 3.2 Programming on Linux
• 4 Uses
o 4.1 Desktop
o 4.2 Servers and supercomputers
o 4.3 Embedded devices
o 4.4 Market share and uptake
• 5 Code size
• 6 Licensing, trademark, and naming
o 6.1 GNU/Linux
• 7 See also
• 8 References
• 9 External links
See also: History of Linux
The Unix operating system was conceived and implemented in the 1960s and first
released in 1970. Its wide availability and portability meant that it was widely adopted,
copied and modified by academic institutions and businesses, with its design being
influential on authors of other systems.
Richard Stallman, founder of the GNU project
The GNU Project, started in 1984, had the goal of creating a "complete Unix-compatible
software system" made entirely of free software. In 1985, Richard Stallman created the
Free Software Foundation and developed the GNU General Public License (GNU GPL).
Many of the programs required in an OS (such as libraries, compilers, text editors, a Unix
shell, and a windowing system) were completed by the early 1990s, although low level
elements such as device drivers, daemons, and the kernel were stalled and incomplete.
Linus Torvalds has said that if the GNU kernel had been available at the time (1991), he
would not have decided to write his own.
MINIX, a Unix-like system intended for academic use, was released by Andrew S.
Tanenbaum in 1987. While source code for the system was available, modification and
redistribution were restricted (that is not the case today). In addition, MINIX's 16-bit
design was not well adapted to the 32-bit design of the increasingly cheap and popular
Intel 386 architecture for personal computers.
Linus Torvalds, creator of the Linux kernel.
In 1991, Torvalds began to work on a non-commercial replacement for MINIX while he
was attending the University of Helsinki. This eventually became the Linux kernel.
In 1992, Tanenbaum posted an article on Usenet claiming Linux was obsolete. In the
article, he criticized the operating system as being monolithic in design and being tied
closely to the x86 architecture and thus not portable, as he described "a fundamental
error." Tanenbaum suggested that those who wanted a modern operating system should
look into one based on the microkernel model. The posting elicited the response of
Torvalds and Ken Thompson, one of the founders of Unix, which resulted in a well
known debate over the microkernel and monolithic kernel designs.
Linux was dependent on the MINIX user space at first. With code from the GNU system
freely available, it was advantageous if this could be used with the fledgling OS. Code
licensed under the GNU GPL can be used in other projects, so long as they also are
released under the same or a compatible license. In order to make the Linux kernel
compatible with the components from the GNU Project, Torvalds initiated a switch from
his original license (which prohibited commercial redistribution) to the GNU GPL.
Linux and GNU developers worked to integrate GNU components with Linux to make a
fully functional and free operating system.
Commercial and popular uptake
Today Linux is used in numerous domains, from embedded systems to
supercomputers, and has secured a place in server installations with the popular LAMP
application stack. Torvalds continues to direct the development of the kernel. Stallman
heads the Free Software Foundation, which in turn supports the GNU components.
Finally, individuals and corporations develop third-party non-GNU components. These
third-party components comprise a vast body of work and may include both kernel
modules and user applications and libraries. Linux vendors and communities combine
and distribute the kernel, GNU components, and non-GNU components, with additional
package management software in the form of Linux distributions.
Linux is a modular Unix-like operating system. It derives much of its basic design from
principles established in Unix during the 1970s and 1980s. Linux uses a monolithic
kernel, the Linux kernel, which handles process control, networking, and peripheral and
file system access. Device drivers are integrated directly with the kernel.
Much of Linux's higher-level functionality is provided by separate projects which
interface with the kernel. The GNU userland is an important part of most Linux systems,
providing the shell and Unix tools which carry out many basic operating system tasks. On
top these tools form a Linux system with a graphical user interface that can be used,
usually running in the X Window System.
This section requires expansion.
See also: User interface
Linux can be controlled by one or more of a text-based command line interface (CLI),
graphical user interface (GUI) (usually the default for desktop), or through controls on
the device itself (common on embedded machines).
On desktop machines, KDE, GNOME and Xfce are the most popular user interfaces,
though a variety of other user interfaces exist. Most popular user interfaces run on top of
the X Window System (X), which provides network transparency, enabling a graphical
application running on one machine to be displayed and controlled from another.
Other GUIs include X window managers such as FVWM, Enlightenment and Window
Maker. The window manager provides a means to control the placement and appearance
of individual application windows, and interacts with the X window system.
A Linux system usually provides a CLI of some sort through a shell, which is the
traditional way of interacting with a Unix system. A Linux distribution specialized for
servers may use the CLI as its only interface. A “headless system” run without even a
monitor can be controlled by the command line via a protocol such as SSH or telnet.
Most low-level Linux components, including the GNU Userland, use the CLI
exclusively. The CLI is particularly suited for automation of repetitive or delayed tasks,
and provides very simple inter-process communication. A graphical terminal emulator
program is often used to access the CLI from a Linux desktop.
Main article: Linux distribution
A summarised history of Unix-like operating systems showing Linux's origins. Note that
despite similar architectural designs and concepts being shared as part of the POSIX
standard, Linux does not share any non-free source code with the original Unix nor
The primary difference between Linux and many other popular contemporary operating
systems is that the Linux kernel and other components are free and open source software.
Linux is not the only such operating system, although it is the best-known and most
widely used. Some free and open source software licences are based on the principle of
copyleft, a kind of reciprocity: any work derived from a copyleft piece of software must
also be copyleft itself. The most common free software license, the GNU GPL, is a form
of copyleft, and is used for the Linux kernel and many of the components from the GNU
As an operating system underdog, Linux aims for interoperability with other operating
systems and established computing standards. Linux systems adhere to POSIX, SUS,
ISO and ANSI standards where possible. To date, however, only the Linux-FT
distribution has been POSIX.1 certified.
Free software projects, although developed in a collaborative fashion, are often produced
independently of each other. However, given that the software licenses explicitly permit
redistribution, this provides a basis for larger scale projects that collect the software
produced by stand-alone projects and make it available all at once in the form of a Linux
A Linux distribution, commonly called a “distro”, is a project that manages a remote
collection of Linux-based software, and facilitates installation of a Linux operating
system. Distributions are maintained by individuals, loose-knit teams, volunteer
organizations, and commercial entities. They include system software and application
software in the form of packages, and distribution-specific software for initial system
installation and configuration as well as later package upgrades and installs. A
distribution is responsible for the default configuration of installed Linux systems, system
security, and more generally integration of the different software packages into a
A command line session using bash
Linux is largely driven by its developer and user communities. Some vendors develop
and fund their distributions on a volunteer basis, Debian being a well-known example.
Others maintain a community version of their commercial distributions, as Red Hat does
In many cities and regions, local associations known as Linux Users Groups (LUGs) seek
to promote Linux and by extension free software. They hold meetings and provide free
demonstrations, training, technical support, and operating system installation to new
users. There are also many Internet communities that seek to provide support to Linux
users and developers. Most distributions and open source projects have IRC chatrooms or
newsgroups. Online forums are another means for support, with notable examples being
LinuxQuestions.org and the Gentoo forums. Linux distributions host mailing lists;
commonly there will be a specific topic such as usage or development for a given list.
There are several technology websites with a Linux focus. Linux Weekly News is a
weekly digest of Linux-related news; the Linux Journal is an online magazine of Linux
articles published monthly; Slashdot is a technology-related news website with many
stories on Linux and open source software; Groklaw has written in depth about Linux-
related legal proceedings and there are many articles relevant to the Linux kernel and its
relationship with GNU on the GNU project's website. Print magazines on Linux often
include cover disks including software or even complete Linux distributions.
Although Linux is generally available free of charge, several large corporations have
established business models that involve selling, supporting, and contributing to Linux
and free software. These include Dell, IBM, HP, Sun Microsystems, Novell, and Red
Hat. The free software licenses on which Linux is based explicitly accommodate and
encourage commercialization; the relationship between Linux as a whole and individual
vendors may be seen as symbiotic. One common business model of commercial suppliers
is charging for support, especially for business users. A number of companies also offer a
specialized business version of their distribution, which adds proprietary support
packages and tools to administer higher numbers of installations or to simplify
administrative tasks. Another business model is to give away the software in order to sell
Programming on Linux
Most Linux distributions support dozens of programming languages. The most common
collection of utilities for building both Linux applications and operating system programs
is found within the GNU toolchain, which includes the GNU Compiler Collection (GCC)
and the GNU build system. Amongst others, GCC provides compilers for Ada, C, C++,
Java, and Fortran. The Linux kernel itself is written to be compiled with GCC.
Proprietary compilers for Linux include the Intel C++ Compiler and IBM XL C/C++
Most distributions also include support for Perl, Ruby, Python and other dynamic
languages. Examples of languages that are less common, but still well-supported, are C#
via the Mono project, and Scheme. A number of Java Virtual Machines and development
kits run on Linux, including the original Sun Microsystems JVM (HotSpot), and IBM's
J2SE RE, as well as many open-source projects like Kaffe. The two main frameworks for
developing graphical applications are those of GNOME and KDE. These projects are
based on the GTK+ and Qt widget toolkits, respectively, which can also be used
independently of the larger framework. Both support a wide variety of languages. There
are a number of Integrated development environments available including Anjuta,
Code::Blocks, Eclipse, KDevelop, Lazarus, MonoDevelop, NetBeans, and Omnis Studio
while the long-established editors Vim and Emacs remain popular.
As well as those designed for general purpose use on desktops and servers, distributions
may be specialized for different purposes including: computer architecture support,
embedded systems, stability, security, localization to a specific region or language,
targeting of specific user groups, support for real-time applications, or commitment to a
given desktop environment. Furthermore, some distributions deliberately include only
free software. Currently, over three hundred distributions are actively developed, with
about a dozen distributions being most popular for general-purpose use.
Linux is a widely ported operating system. While the Linux kernel was originally
designed only for Intel 80386 microprocessors, it now runs on a more diverse range of
computer architectures than any other operating system: in the hand-held ARM-based
iPAQ and the mainframe IBM System z9, in devices ranging from mobile phones to
supercomputers. Specialized distributions exist for less mainstream architectures. The
ELKS kernel fork can run on Intel 8086 or Intel 80286 16-bit microprocessors, while the
µClinux kernel fork may run on systems without a memory management unit. The kernel
also runs on architectures that were only ever intended to use a manufacturer-created
operating system, such as Macintosh computers, PDAs, video game consoles, portable
music players, and mobile phones.
A KDE 4 desktop.
A GNOME 2.20 desktop.
Main article: Desktop Linux
Although there is a lack of Linux ports for some Mac OS X and Microsoft Windows
programs in domains such as desktop publishing and professional audio,
applications equivalent to those available for Mac and Windows are available for Linux.
Most Linux distributions provide a program for browsing a list of thousands of free
software applications that have already been tested and configured for a specific
distribution. These free programs can be downloaded and installed with one mouse click
and a digital signature guarantees that no one has added a virus or a spyware to these
Many free software titles that are popular on Windows, such as Pidgin, Mozilla Firefox,
Openoffice.org, and GIMP, are available for Linux. A growing amount of proprietary
desktop software is also supported under Linux, examples being Adobe Flash Player,
Acrobat Reader, Matlab, Nero Burning ROM, Opera, Google Picasa, RealPlayer, and
Skype. In the field of animation and visual effects, most high end software, such as
AutoDesk Maya, Softimage XSI and Apple Shake, is available for Linux, Windows and/
or Mac OS X. CrossOver is a proprietary solution based on the open source Wine project
that supports running older Windows versions of Microsoft Office and Adobe Photoshop
versions through CS2. Microsoft Office 2007 and Adobe Photoshop CS3 are known not
Besides the free Windows compatibility layer Wine, most distributions offer Dual boot
and X86 virtualization for running both Linux and Windows on the same computer.
Linux's open nature allows distributed teams to localize Linux distributions for use in
locales where localizing proprietary systems would not be cost-effective. For example the
Sinhalese language version of the Knoppix distribution was available for a long time
before Microsoft Windows XP was translated to Sinhalese. In this case the Lanka Linux
User Group played a major part in developing the localized system by combining the
knowledge of university professors, linguists, and local developers.
The performance of Linux on the desktop has been a controversial topic, with at least one
key Linux kernel developer, Con Kolivas, accusing the Linux community of favouring
performance on servers. He quit Linux development because he was frustrated with this
lack of focus on the desktop, and then gave a 'tell all' interview on the topic.
See also: Linux gaming
Servers and supercomputers
Historically, Linux has mainly been used as a server operating system, and has risen to
prominence in that area; Netcraft reported in February 2008 that five of the ten most
reliable internet hosting companies run Linux on their web servers. This is due to its
relative stability and long uptime, and the fact that desktop software with a graphical user
interface for servers is often unneeded. Enterprise and non-enterprise Linux distributions
may be found running on servers. Linux is the cornerstone of the LAMP server-software
combination (Linux, Apache, MySQL, Perl/PHP/Python) which has achieved popularity
among developers, and which is one of the more common platforms for website hosting.
Linux is commonly used as an operating system for supercomputers. As of November
2007, out of the top 500 systems, 426 (85.2%) run Linux.
Main article: Embedded Linux
See also: Linux devices
Due to its low cost and ability to be easily modified, an embedded Linux is often used in
embedded systems. Linux has become a major competitor to the proprietary Symbian OS
found in the majority of smartphones — 16.7% of smartphones sold worldwide during
2006 were using Linux — and it is an alternative to the proprietary Windows CE and
Palm OS operating systems on mobile devices. Cell phones or PDAs running on Linux
and built on open source platform became a trend from 2007, like Nokia N810,
Openmoko's Neo1973 and the on-going Google Android. The popular TiVo digital video
recorder uses a customized version of Linux. Several network firewall and router
standalone products, including several from Linksys, use Linux internally, using its
advanced firewall and routing capabilities. The Korg OASYS and the Yamaha Motif XS
music workstations also run Linux. Further more Linux is used in the leading stage
lighting control system, FlyingPig/HighEnd WholeHogIII Console .
Market share and uptake
Main article: Linux adoption
Many quantitative studies of open source software focus on topics including market share
and reliability, with numerous studies specifically examining Linux. The Linux market
is growing rapidly, and the revenue of servers, desktops, and packaged software running
Linux is expected to exceed $35.7 billion by 2008.
IDC's report for Q1 2007 says that Linux now holds 12.7% of the overall server market.
This estimate was based on the number of Linux servers sold by various companies.
Desktop adoption of Linux is approximately 1%. In comparison, Microsoft operating
systems hold more than 90%.
The frictional cost of switching operating systems and lack of support for certain
hardware and application programs designed for Microsoft Windows have been two
factors that have inhibited adoption. Proponents and analysts attribute the relative success
of Linux to its security, reliability, low cost, and freedom from vendor lock-in.
Also most recently Google has begun to fund Wine, which acts as a compatibility layer,
allowing users to run some Windows programs under Linux.
The XO laptop project of One Laptop Per Child is creating a new and potentially much
larger Linux community, planned to reach several hundred million schoolchildren and
their families and communities in developing countries. Six countries have ordered a
million or more units each for delivery in 2007 to distribute to schoolchildren at no
charge. Google, Red Hat, and eBay are major supporters of the project.
See also: Usage share of desktop operating systems
A 2001 study of Red Hat Linux 7.1 found that this distribution contained 30 million
source lines of code. Using the Constructive Cost Model, the study estimated that this
distribution required about eight thousand man-years of development time. According to
the study, if all this software had been developed by conventional proprietary means, it
would have cost about 1.08 billion dollars (year 2000 U.S. dollars) to develop in the
Most of the code (71%) was written in the C programming language, but many other
languages were used, including C++, assembly language, Perl, Python, Fortran, and
various shell scripting languages. Slightly over half of all lines of code were licensed
under the GPL. The Linux kernel itself was 2.4 million lines of code, or 8% of the total.
In a later study, the same analysis was performed for Debian GNU/Linux version 4.0.
This distribution contained over 283 million source lines of code, and the study estimated
that it would have cost 5.4 billion Euros to develop by conventional means.
Licensing, trademark, and naming
The Linux kernel and most GNU software are licensed under the GNU General Public
License (GPL). The GPL requires that anyone who distributes the Linux kernel must
make the source code (and any modifications) available to the recipient under the same
terms. In 1997, Linus Torvalds stated, “Making Linux GPL'd was definitely the best
thing I ever did.” Other key components of a Linux system may use other licenses;
many libraries use the GNU Lesser General Public License (LGPL), a more permissive
variant of the GPL, and the X Window System uses the MIT License.
Torvalds has publicly stated that he would not move the Linux kernel (currently licensed
under GPL version 2) to version 3 of the GPL, released in mid-2007, specifically citing
some provisions in the new license which prohibit the use of the software in digital rights
In the United States, the name Linux is a trademark registered to Linus Torvalds.
Initially, nobody registered it, but on August 15, 1994, William R. Della Croce, Jr. filed
for the trademark Linux, and then demanded royalties from Linux distributors. In 1996,
Torvalds and some affected organizations sued him to have the trademark assigned to
Torvalds, and in 1997 the case was settled. The licensing of the trademark has since
been handled by the Linux Mark Institute. Torvalds has stated that he only trademarked
the name to prevent someone else from using it, but was bound in 2005 by United States
trademark law to take active measures to enforce the trademark. As a result, the LMI sent
out a number of letters to distribution vendors requesting that a fee be paid for the use of
the name, and a number of companies have complied.
See also: SCO-Linux controversies
Main article: GNU/Linux naming controversy
The Free Software Foundation views Linux distributions which use GNU software as
GNU variants and they ask that such operating systems be referred to as GNU/Linux or a
Linux-based GNU system. However, the media and population at large refers to this
family of operating systems simply as Linux. While some distributors make a point of
using the aggregate form, most notably Debian with the Debian GNU/Linux distribution,
the term's use outside of the enthusiast community is limited. The distinction between the
Linux kernel and distributions based on it plus the GNU system is a source of confusion
to many newcomers, and the naming remains controversial.