Linux
This article is about the operating system. For the kernel, see Linux kernel. For other uses, see Linux (disambiguation).
Linux (pronounced i/ˈlɪnəks/ LIN-əks[4][5] or, less frequently, /ˈlaɪnəks/ LYN-əks[5][6]) is a Unix-like and mostlyPOSIX-compliant[7] computer operating system (OS) assembled under the model offree and open-source software development and distribution. The defining component of Linux is theLinux kernel,[8]anoperating system kernelfirst released on 5 October 1991 byLinus Torvalds.[9][10] The Free Software Foundationuses the
nameGNU/Linux to describe the operating system, which
has led to somecontroversy.[11][12]
Linux was originally developed as a free operating sys-tem forpersonal computers based on the Intel x86 ar-chitecture, but has since beenportedto more computer hardware platforms than any other operating system.[13] Thanks to its dominance onsmartphones,Android, which is built on top of the Linux kernel, has thelargest installed baseof all general-purpose operating systems.[14]Linux, in its original form, is also the leading operating system onserversand otherbig ironsystems such asmainframe computersandsupercomputers,[15][16]but is used on only around 1.5% ofdesktop computers[17]with Linux-based Chrome OStaking about 5% of the overall and nearly 20% of the sub-$300notebooksales.[18]Linux also runs on embedded systems, which are devices whose oper-ating system is typically built into thefirmware and is highly tailored to the system; this includes smartphones andtablet computersrunning Android and other Linux derivatives,[19] TiVoand similarDVR devices, network routers, facility automation controls, televisions,[20][21] video game consoles, andsmartwatches.[22]
The development of Linux is one of the most prominent examples of free and open-source software collabora-tion. The underlyingsource codemay be used, modified and distributed—commercially or non-commercially— by anyone under the terms of its respective licenses, such as theGNU General Public License. Typically, Linux ispackagedin a form known as aLinux distribution, for both desktop and server use. Some of the popular main-stream Linux distributions are Debian, Ubuntu, Linux Mint,Fedora,openSUSE,Arch LinuxandGentoo, to-gether with commercialRed Hat Enterprise Linux and SUSE Linux Enterprise Serverdistributions. Linux dis-tributions include the Linux kernel, supporting utilities andlibraries, and usually a large amount of application software to fulfill the distribution’s intended use.
Distributions oriented toward desktop use typically in-clude X11, a Wayland implementation or Mir as the windowing system, and an accompanyingdesktop envi-ronmentsuch asGNOMEor theKDE Software Compila-tion; some distributions may also include a less resource-intensive desktop such asLXDEorXfce. Distributions intended to run on servers may omit all graphical environ-ments from the standard install, and instead include other software to set up and operate asolution stacksuch as LAMP. Because Linux is freely redistributable, anyone may create a distribution for any intended use.
1 History
Main article:History of Linux
1.1 Antecedents
Linus Torvalds, principal author of theLinux kernel
The Unix operating system was conceived and im-plemented in 1969 at AT&T's Bell Laboratories in the United States by Ken Thompson, Dennis Ritchie,
2 1 HISTORY
Douglas McIlroy, andJoe Ossanna.[23] First released in 1971, Unix was written entirely inassembly languageas it was common practice at the time. Later, in a key pio-neering approach in 1973, it was rewritten in theC pro-gramming language byDennis Ritchie(with exceptions to the kernel and I/O). The availability of ahigh-level lan-guageimplementation of Unix made itsportingto differ-ent computer platforms easier.
Due to an earlier antitrust case forbidding it from en-tering the computer business, AT&T was required to li-cense the operating system’s source code to anyone who asked.[24] As a result, Unix grew quickly and became widely adopted by academic institutions and businesses. In 1984, AT&T divested itself of Bell Labs; freed of the legal obligation requiring free licensing, Bell Labs began selling Unix as aproprietaryproduct.
TheGNU Project, started in 1983 byRichard Stallman, had the goal of creating a “complete Unix-compatible software system” composed entirely of free software. Work began in 1984.[25]Later, in 1985, Stallman started theFree Software Foundationand wrote theGNU Gen-eral Public License(GNU GPL) in 1989. By the early 1990s, many of the programs required in an operating system (such as libraries,compilers,text editors, aUnix shell, and awindowing system) were completed, although low-level elements such asdevice drivers,daemons, and thekernelwere stalled and incomplete.[26]
Linus Torvalds has said that if theGNU kernelhad been available at the time (1991), he would not have decided to write his own.[27]
Although not released until 1992 due to legal compli-cations, development of386BSD, from whichNetBSD, OpenBSD and FreeBSD descended, predated that of Linux. Torvalds has said that if 386BSD had been avail-able at the time, he probably would not have created Linux.[28]
MINIX was created by a computer science professor Andrew S. Tanenbaumand released in 1987 as a minimal Unix-likeoperating system targeted at students and oth-ers who wanted to learn the operating system principles. Although the complete source code of MINIX was freely available, the licensing terms prevented it from beingfree softwareuntil the licensing changed in April 2000.[29]
1.2
Creation
In 1991, while attending theUniversity of Helsinki, Tor-valds became curious about operating systems[30] and frustrated by the licensing of MINIX, which at the time limited it to educational use only.[29] He began to work on his own operating system kernel, which eventually be-came theLinux kernel.
Torvalds began the development of the Linux kernel on MINIX and applications written for MINIX were also used on Linux. Later, Linux matured and further Linux
kernel development took place on Linux systems.[31] GNU applications also replaced all MINIX components, because it was advantageous to use the freely available code from the GNU Project with the fledgling operat-ing system; code licensed under the GNU GPL can be reused in other projects as long as they also are released under the same or a compatible license. Torvalds ini-tiated a switch from his original license, which prohib-ited commercial redistribution, to the GNU GPL.[32] De-velopers worked to integrate GNU components with the Linux kernel, making a fully functional and free operating system.[26]
1.3 Naming
5.25-inchfloppy discsholding a very early version of Linux
Linus Torvalds had wanted to call his invention Freax, a portmanteauof “free”, “freak”, and “x” (as an allusion to Unix). During the start of his work on the system, he stored the files under the name “Freax” for about half of a year. Torvalds had already considered the name “Linux,” but initially dismissed it as too egotistical.[33]
In order to facilitate development, the files were uploaded to theFTP server(ftp.funet.fi) ofFUNETin September 1991. Ari Lemmke, Torvald’s coworker at theHelsinki University of Technology (HUT) who was one of the volunteer administrators for the FTP server at the time, did not think that “Freax” was a good name. So, he named the project “Linux” on the server without consult-ing Torvalds.[33] Later, however, Torvalds consented to “Linux”.
To demonstrate how the word “Linux” should be pro-nounced ( i/ˈlɪnəks/ LIN-əks[4][5]), Torvalds included an audio guide ( listen) with the kernel source code.[34] Another variant of pronunciation is /ˈlaɪnəks/ LYN-əks.[5][6]
1.5 Current development 3
1.4
Commercial and popular uptake
Ubuntu, a popular Linux distribution
Main article:Linux adoption
Adoption of Linux in production environments, rather
Nexus 5runningAndroid
than being used only by hobbyists, started to take off first in the mid-1990s in the supercomputing community, where organizations such as NASA started to replace their increasingly expensive machines withclustersof in-expensive commodity computers running Linux. Com-mercial use followed when Delland IBM, followed by Hewlett-Packard, started offering Linux support to es-capeMicrosoft's monopoly in the desktop operating sys-tem market.[35]
Today, Linux systems are used in every domain, from embedded systems to supercomputers,[16][36] and have secured a place in server installations often using the popularLAMPapplication stack.[37] Use of Linux dis-tributions in home and enterprise desktops has been growing.[38][39][40][41][42][43][44] Linux distributions have also become popular in thenetbookmarket, with many devices shipping with customized Linux distributions in-stalled, and Google releasing their ownGoogle Chrome OSdesigned for netbooks.
Linux’s greatest success in the consumer market is per-haps the mobile device market, withAndroidbeing one of the most dominant operating systems onsmartphones and very popular on tablets and, more recently, on
wearables. Linux gaming is also on the rise withValve showing its support for Linux and rolling out its own gam-ing oriented Linux distribution. Linux distributions have also gained popularity with various local and national gov-ernments, such as the federal government of Brazil.[45]
1.5 Current development
Torvalds continues to direct the development of the kernel.[46] Stallman heads the Free Software Foundation,[47] which in turn supports the GNU components.[48] Finally, individuals and corporations develop 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 compo-nents, with additionalpackage managementsoftware in the form ofLinux distributions.
2 Design
A Linux-based system is a modular Unix-like operat-ing system, derivoperat-ing much of its basic design from prin-ciples established in Unix during the 1970s and 1980s. Such a system uses amonolithic kernel, theLinux kernel, which handles process control, networking, access to the peripherals, andfile systems. Device driversare either integrated directly with the kernel, or added as modules that are loaded while the system is running.[49]
Separate projects that interface with the kernel provide much of the system’s higher-level functionality. The GNUuserlandis an important part of most Linux-based systems, providing the most common implementation of theC library, a popularCLI shell, and many of the com-monUnix toolswhich carry out many basic operating sys-tem tasks. Thegraphical user interface(or GUI) used by most Linux systems is built on top of an implementation of theX Window System.[50] More recently, the Linux community seeks to advance toWaylandas the new dis-play server protocol in place ofX11; Ubuntu, however, developsMirinstead of Wayland.[51]
Installed components of a Linux system include the following:[50][52]
• A bootloader, for example GNU GRUB, LILO, SYSLINUX, Corebootor Gummiboot. This is a program that loads the Linux kernel into the com-puter’s main memory, by being executed by the computer when it is turned on and after thefirmware initialization is performed.
• Aninitprogram, such as the traditionalsysvinitand the newersystemd,OpenRCandUpstart. This is the
4 2 DESIGN
firstprocesslaunched by the Linux kernel, and is at the root of the process tree: in other terms, all pro-cesses are launched through init. It starts propro-cesses such as system services and login prompts (whether graphical or in terminal mode).
• Software libraries, which contain code that can be used by running processes. On Linux systems us-ingELF-format executable files, thedynamic linker that manages use of dynamic libraries is known as ld-linux.so. If the system is set up for the user to compile software themselves,header fileswill also be included to describe theinterfaceof installed braries. Beside the most commonly used software li-brary on Linux systems, theGNU C Library(glibc), there are numerous other libraries.
• C standard libraryis the library needed to run standardC programson a computer system, with the GNU C Library being the most com-monly used. Several alternatives are available, such as theEGLIBC(which was used by De-bian for some time) anduClibc(which was de-signed foruClinux).
• Widget toolkitsare the libraries used to build graphical user interfaces(GUIs) for software applications. Numerous widget toolkits are available, includingGTK+andClutter (soft-ware) developed by the GNOME project, Qt developed by the Qt Project and led byDigia, andEnlightenment Foundation Li-braries (EFL) developed primarily by the Enlightenmentteam.
• User interface programs such as command shells or
windowing environments.
2.1
User interface
The user interface, also known as theshell, is either a command-line interface (CLI), a graphical user inter-face (GUI), or through controls attached to the associ-ated hardware, which is common for embedded systems. For desktop systems, the default mode is usually a graph-ical user interface, although the CLI is available through terminal emulatorwindows or on a separatevirtual con-sole.
CLIshells are the text-based user interfaces, which use text for both input and output. The dominant shell used in Linux is theGNU Bourne-Again Shell(bash), originally developed for theGNU project. Most low-level Linux components, including various parts of theuserland, use the CLI exclusively. The CLI is particularly suited for automation of repetitive or delayed tasks, and provides very simpleinter-process communication.
On desktop systems, the most popular user interfaces are the GUI shells, packaged together with extensive
Bash, ashelldeveloped byGNU[53]and widely used in Linux
desktop environments, such as the K Desktop Envi-ronment (KDE), GNOME, Cinnamon, Unity, LXDE, PantheonandXfce, though a variety of additional user in-terfaces exist. Most popular user inin-terfaces are based on theX Window System, often simply called “X”. It pro-videsnetwork transparencyand permits a graphical appli-cation running on one system to be displayed on another where a user may interact with the application; however, certain extensions of the X Window System are not ca-pable of working over the network.[54]Several popular X display servers exist, with the reference implementation, X.Org Server, being the most popular.
Several types ofwindow managersexist for X11, includ-ingtiling,dynamic,stackingandcompositing. Window managers provide means to control the placement and ap-pearance of individual application windows, and interact with the X Window System. SimplerX window man-agerssuch asdwmorratpoisonprovide aminimalist func-tionality, while more elaborate window managers such as FVWM,EnlightenmentorWindow Makerprovide more features such as a built-in taskbar and themes, but are still lightweight when compared to desktop environments. Desktop environments include window managers as part of their standard installations, such asMutter(GNOME), KWin(KDE) orXfwm(xfce), although users may choose to use a different window manager if preferred.
Wayland is a display server protocol intended as a re-placement for the X11 protocol; as of 2014, Wayland has not received wider adoption. Unlike X11, Wayland does not need an external window manager and composit-ing manager. Therefore, a Wayland compositor takes the role of the display server, window manager and composit-ing manager. Weston is the reference implementation of Wayland, while GNOME’s Mutter and KDE’s KWin are being ported to Wayland as standalone display servers.
3.1 Community 5
Enlightenment has already been successfully ported to Wayland since version 19.
2.2
Video input infrastructure
Main article:Video4Linux
Linux currently has two modern kernel-userspace APIs for handing video input devices: V4L2 API for video streams and radio, and DVB API for digital TV reception.[55]
Due to the complexity and diversity of different devices, and due to the large amount of formats and standards han-dled by those APIs, this infrastructure needs to evolve to better fit other devices. Also, a good userspace device library is the key of the success for having userspace ap-plications to be able to work with all formats supported by those devices.[56][57]
3
Development
System III & V family
BSD (Berkeley Software Distribution) FreeBSD NetBSD OpenBSD SunOS Solaris NextStep Mac OS X Xenix OS GNU GNU/Linux Commercial UNIX HP-UX AIX UnixWare IRIX BSD family 1970 1980 1990 2000 Time Microsoft/SCO Richard Stallman Darwin GNU/Hurd K16 Linus Torvalds Andrew S. Tanenbaum Minix 9.1 6.0.1 5.3 11 11/11 10.8.4 3.3 3.10.9 3.2.1 11i v3 7.1 TL1 6.5.30 4.1.4 Research UNIX 10.5
Bell Labs: Ken Thompson, Dennis Ritchie, et al.
Bill Joy Sun Microsystems AT&T IBM SGI Univel/SCO Apple 2010 4.4
Simplified history ofUnix-likeoperating systems. Linux shares similar architecture and concepts (as part of thePOSIXstandard) but does not share non-free source code with the originalUnixor
MINIX.
Main articles:Linux distributionandFree software
The primary difference between Linux and many other popular contemporary operating systems is that theLinux kernel and other components arefree andopen-source software. Linux is not the only such operating system, although it is by far the most widely used.[58]Somefree andopen-sourcesoftware licenses are based on the prin-ciple ofcopyleft, a kind of reciprocity: any work derived from a copyleft piece of software must also be copyleft itself. The most common free software license, theGNU General Public License(GPL), is a form of copyleft, and is used for the Linux kernel and many of the components from theGNU Project.
Linux based distributions are intended by developers forinteroperabilitywith other operating systems and es-tablished computing standards. Linux systems adhere toPOSIX,[59] SUS,[60] LSB, ISO, and ANSI standards where possible, although to date only one Linux distribu-tion has been POSIX.1 certified, Linux-FT.[61][62] Free software projects, although developed through collaboration, are often produced independently of each other. The fact that the software licenses explicitly permit redistribution, however, 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 distribution.
Many Linux distributions, or “distros”, manage a remote collection of system software and application software packages available for download and installation through a network connection. This allows users to adapt the op-erating system to their specific needs. Distributions are maintained by individuals, loose-knit teams, volunteer organizations, and commercial entities. A distribution is responsible for the default configuration of the installed Linux kernel, general system security, and more gener-ally integration of the different software packages into a coherent whole. Distributions typically use apackage managersuch asapt,yum,zypper,pacmanorportageto install, remove and update all of a system’s software from one central location.
3.1 Community
See also: Free software community and Linux User Group
A distribution is largely driven by its developer and user communities. Some vendors develop and fund their dis-tributions on a volunteer basis, Debian being a well-known example. Others maintain a community version of their commercial distributions, asRed Hatdoes with FedoraandSUSEdoes withopenSUSE.
In many cities and regions, local associations known as Linux User Groups (LUGs) seek to promote their pre-ferred distribution and by extension free software. They hold meetings and provide free demonstrations, train-ing, technical support, and operating system installation to new users. Many Internet communities also provide support to Linux users and developers. Most distri-butions and free software / open-source projects have IRCchatrooms ornewsgroups. Online forumsare an-other means for support, with notable examples being LinuxQuestions.organd the various distribution specific support and community forums, such as ones forUbuntu, Fedora, and Gentoo. Linux distributions host mailing lists; commonly there will be a specific topic such as us-age or development for a given list.
6 4 HARDWARE SUPPORT
focus. Print magazines on Linux often include cover disksincluding software or even complete Linux distributions.[63][64]
Although Linux distributions are generally available with-out charge, several large corporations sell, support, and contribute to the development of the components of the system and offree software. An analysis of the Linux ker-nel showed 75 percent of the code from December 2008 to January 2010 was developed by programmers working for corporations, leaving about 18 percent to volunteers and 7% unclassified.[65]Major corporations that provide contributions include Dell, IBM, HP,Oracle, Sun Mi-crosystems(now part of Oracle),SUSE, andNokia. A number of corporations, notablyRed Hat,Canonical, and SUSE, have built a significant business around Linux dis-tributions.
The free software licenses, on which the various soft-ware packages of a distribution built on the Linux kernel are based, explicitly accommodate and encourage com-mercialization; the relationship between a Linux distri-bution as a whole and individual vendors may be seen as symbiotic. One common business model of com-mercial 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 adminis-ter higher numbers of installations or to simplify admin-istrative tasks.
Another business model is to give away the software in order to sell hardware. This used to be the norm in the computer industry, with operating systems such asCP/M, Apple DOSand versions ofMac OSprior to 7.6 freely copyable (but not modifiable). As computer hardware standardized throughout the 1980s, it became more diffi-cult for hardware manufacturers to profit from this tactic, as the OS would run on any manufacturer’s computer that shared the same architecture.
3.2
Programming on Linux
Linux distributions support dozens ofprogramming lan-guages. The original development tools used for build-ing both Linux applications and operatbuild-ing system pro-grams are found within the GNU toolchain, which in-cludes the GNU Compiler Collection (GCC) and the GNU build system. Amongst others, GCC provides com-pilers forAda,C,C++,GoandFortran. Many program-ming languages have a cross-platform reference imple-mentation that supports Linux, for example PHP,Perl, Ruby, Python, Java, Go, Rust and Haskell. First re-leased in 2003, the LLVMproject provides an alterna-tive cross-platform open-source compiler for many lan-guages.Proprietarycompilers for Linux include theIntel C++ Compiler,Sun Studio, and IBM XLC/C++ Com-piler. BASICin the form ofVisual Basicis supported in such forms asGambas,FreeBASIC, andXBasic, and
in terms of terminal programming or QuickBASIC or Turbo BASICprogramming in the form ofQB64. A common feature of Unix-like systems, Linux includes traditional specific-purpose programming languages tar-geted atscripting, text processing and system configura-tion and management in general. Linux distribuconfigura-tions sup-portshell scripts,awk,sedandmake. Many programs also have an embedded programming language to support configuring or programming themselves. For example, regular expressionsare supported in programs likegrep, orlocate, while advanced text editors, likeGNU Emacs, have a completeLispinterpreter built-in.
Most distributions also include support for PHP, Perl, Ruby,Pythonand otherdynamic languages. While not as common, Linux also supportsC#(viaMono),Vala, and Scheme. A number ofJava Virtual Machinesand devel-opment kits run on Linux, including the original Sun Mi-crosystems JVM (HotSpot), and IBM’s J2SE RE, as well as many open-source projects likeKaffeandJikesRVM. GNOME and KDE are popular desktop environments and provide a framework for developing applications. These projects are based on the GTK+and Qt widget toolkits, respectively, which can also be used indepen-dently of the larger framework. Both support a wide va-riety of languages. There are a number of Integrated development environments available including Anjuta, Code::Blocks, CodeLite, Eclipse, Geany, ActiveState Komodo,KDevelop,Lazarus,MonoDevelop,NetBeans, andQt Creator, while the long-established editorsVim, nanoandEmacsremain popular.[66]
4 Hardware support
Hardware
Desktop Computer Workstation Home Computer Desktop replacement laptop
Thin client Mobile computer
Note-/ Net-/ Smartbook Tablet Smartphone PDA / Handheld game console Wearable Computer
Wristwatch Virtual Retina Display Head-mounted display Embedded Computer Customer-premises equipment Measurement Equipment Laboratory Equipment Layer3-Switches other embedded systems Supercomputer Computer Cluster Mainframe computer
Linux Network scheduler Network stack
Netfilter Linux device drivers Linux file system drivers Linux Process Scheduler Linux Security Modules
Linux kernel Human-Machine-Interface Speech recognition Attitude sensor Motion sensor Display, Sound Vibration Keyboard & Mouse also Braille, Touch-Display, Speech recognition, Graphics tablet, 3D-Mouse, Wii nunchak, etc.
Touch-Display Attitude sensor, Motion sensor, Speech recognition remote (SSH, HTTP, ...) remote (SSH, HTTP, Serial, I2C, ...)
Pool of free and open-source and
proprietary software
High-performance computing (HPC) Real-time computing
(RTC)
Graphical User Interfaces
(Shells) Distributed computing Wearable UI Touch UI Desktop UI Office Image Processing Desktop Publishing (DTP)
Digital Audio Workstation DJ Mixing Software Software Development Package management systems Web server solution stacks (LAMP)
Routing daemons
Home cinema solutions Distributed Computing
CAD, CAM & CAE Software
Windowing Systems
Video processing software 3D computer graphics Computer animation
Motion graphics
Debian software archives: 37,000 software packages
Video games
Linux is ubiquitously found on various types of hardware.
See also:List of Linux-supported computer architectures
Linux kernel is a widelyportedoperating system kernel; it runs on a highly diverse range ofcomputer architec-tures, including the hand-heldARM-basediPAQand the IBM mainframes System z9orSystem z10– covering de-vices ranging from mobile phones to supercomputers.[67] Specialized distributions and kernel forks exist for less mainstream architectures; for example, the ELKS
ker-5.1 Desktop 7
nelforkcan run onIntel 8086orIntel 80286 16-bit mi-croprocessors, while the µClinux kernel fork may run on systems without a memory management unit. The kernel also runs on architectures that were only ever in-tended to use a manufacturer-created operating system, such as Macintoshcomputers (with bothPowerPC and Intelprocessors), PDAs,video game consoles,portable music players, and mobile phones.
There are several industry associations and hardware conferences devoted to maintaining and improving support for diverse hardware under Linux, such as FreedomHEC. Over time, support for different hardware has improved in Linux, resulting in any off-the-shelf pur-chase having a “good chance” of being compatible.[68]
5
Uses
See also:Linux range of use
Beside the Linux distributions designed for general-purpose use on desktops and servers, distributions may be specialized for different purposes including:computer architecturesupport,embedded systems, stability, secu-rity, localization to a specific region or language, target-ing of specific user groups, support forreal-time appli-cations, or commitment to a given desktop environment. Furthermore, some distributions deliberately include only free software. As of 2015, over four hundred Linux tributions are actively developed, with about a dozen dis-tributions being most popular for general-purpose use.[69]
5.1
Desktop
libinput
possibly adaptations to Wayland/Mir possibly adaptations to Wayland/Mir possibly adaptations to Wayland/Mir
libxserver X-Server X.Org Xfree86 X-Win32 X11.app window manager metacity mutter KWin Compiz
Linux kernel, device drivers & other modules netfilter
radeon nouveau lima etna_viv freedreno tegra-re ? kdbus ? evdev kms (Kernel Mode Setting)
Hardware drm (Direct Rendering Manager)
D-Bus-Daemon
CPU & GPU cache coherent L2-Caches main memory
Keyboard & Mouse Touch-Screen BrailleDisplay Ethernet 802.11-(abc) Bluetooth UMTS/CDMA/LTE GPS-receiver G-sensor systemd(contains udev) unetworkNetworkManager
pack
agekitd
P
ulseAudio
-d
ALSA: emu20k1, ctxfi, hda... ath9k
kmod-fs-ext4
kmod-ltq-atm-vr9 Media Application 3D Application 2D Application SELinux TOMOYO Smack AppArmor udisks System daemons: avahi-daemon
User Interface Toolkits (in the form of libraries):
glibc µClibc GLib GObject Glib GModule GThread GIO System libraries: libwayland-server Wayland Compositor
weston, clayton, mutter, KWin GNOME Shell Plasma 2 Cair
o -Dock Cinnamon Desktop Shells: Display server: Qt libwayland-client GTK+ Pango Cairo (Xr) libwayland / COGL ATK EFL libwayland-client libwayland-clientSDL
Alternative display servers: D e s k t o p w i d g e t s Enlight. DR19 SF SurfaceFlingerwindow manager AWM libmir-serv mir mir window manager Compiz libbionic libhybris Unity Ubuntu Android Widgets for Unity and Plasma Clutter GNUstep wxWidgets FLTK ... libwayland-client libX/libXCB Linux kernel (Android-forked) binder ashmem pmem
logger
wakelocks ...
Visible software components of the Linux desktop stack in-clude thedisplay server,widget engines, and some of the more widespreadwidget toolkits. There are also components not di-rectly visible to end users, includingD-BusandPulseAudio.
See also: Desktop environment and Linux adoption: Measuring desktop adoption
The popularity of Linux on standard desktop computers and laptops has been increasing over the years.[70] Cur-rently most distributions include a graphical user envi-ronment, with the two most popular environments being GNOME(which can utilize additionalshellssuch as the
defaultGNOME ShellandUbuntu Unity), and theKDE Plasma Desktop.
No single official Linux desktop exists: rather desk-top environments and Linux distributions select compo-nents from a pool offree and open-source softwarewith which they construct a GUI implementing some more or less strict design guide. GNOME, for example, has its human interface guidelinesas a design guide, which gives thehuman–machine interfacean important role, not just when doing the graphical design, but also when consid-ering people withdisabilities, and even when focusing on security.[71]
The collaborative nature of free software development al-lows distributed teams to performlanguage localization of some Linux distributions for use in locales where local-izing proprietary systems would not be cost-effective. For example, theSinhalese languageversion of theKnoppix distribution became available significantly before Mi-crosoft translated Windows XPinto Sinhalese. In this case theLanka Linux User Groupplayed a major part in developing the localized system by combining the knowl-edge of university professors,linguists, and local devel-opers.
5.1.1 Performance and applications
The performance of Linux on the desktop has been a controversial topic; for example in 2007Con Kolivas ac-cused the Linux community of favoring performance on servers. He quit Linux kernel development out of frus-tration with this lack of focus on the desktop, and then gave a “tell all” interview on the topic.[72] Since then a significant amount of development has focused on im-proving the desktop experience. Projects such asUpstart andsystemdaim for a faster boot time; the Wayland and Mir projects aim at replacingX11while enhancing desk-top performance, security and appearance.[73]
Many popular applications are available for a wide vari-ety of operating systems. For example,Mozilla Firefox, OpenOffice.org/LibreOfficeandBlenderhave download-able versions for all major operating systems. Further-more, some applications initially developed for Linux, such asPidgin, andGIMP, were ported to other operating systems (includingWindowsandMac OS X) due to their popularity. In addition, a growing number of proprietary desktop applications are also supported on Linux,[74]such asAutodesk Maya, Softimage XSI andApple Shake in the high-end field of animation and visual effects; see the List of proprietary software for Linuxfor more details. There are alsoseveral companiesthat have ported their own or other companies’ games to Linux, with Linux also being a supported platform on both the popularSteam andDesuradigital-distribution services.[75]
Many other types of applications available for Microsoft Windows and Mac OS X also run on Linux. Commonly, either afree softwareapplication will exist which does the
8 5 USES
functions of an application found on another operating system, or that application will have a version that works on Linux, such as withSkypeand somevideo gameslike Dota 2 and Team Fortress 2. Furthermore, the Wine project provides a Windows compatibility layer to run unmodified Windows applications on Linux. It is spon-sored by commercial interests including CodeWeavers, which produces a commercial version of the software. Since 2009, Google has also provided funding to the Wine project.[76][77] CrossOver, a proprietary solution based on the open-source Wine project, supports run-ning Windows versions ofMicrosoft Office,Intuit appli-cations such asQuickenandQuickBooks,Adobe Photo-shopversions through CS2, and many popular games such asWorld of Warcraft. In other cases, where there is no Linux port of some software in areas such asdesktop pub-lishing[78]andprofessional audio,[79][80][81]there is equiv-alent software available on Linux.
5.1.2 Components and installation
Besides externally visible components, such asX window managers, a non-obvious but quite central role is played by the programs hosted byfreedesktop.org, such as D-Bus or PulseAudio; both major desktop environments (GNOME and KDE) include them, each offering graph-ical front-ends written using the corresponding toolkit (GTK+orQt). Adisplay serveris another component, which for the longest time has been communicating in the X11 display server protocol with its clients; promi-nent software talking X11 includes theX.Org Serverand Xlib. Frustration over the cumbersome X11 core proto-col, and especially over its numerous extensions, has led to the creation of a new display server protocol, Wayland. Installing, updating and removing software in Linux is typically done through the use of package managers such as theSynaptic Package Manager,PackageKit, andYum Extender. While most major Linux distributions have ex-tensive repositories, often containing tens of thousands of packages, not all the software that can run on Linux is available from the official repositories. Alternatively, users can install packages from unofficial repositories, download pre-compiled packages directly from websites, or compile the source code by themselves. All these methods come with different degrees of difficulty; com-piling the source code is in general considered a challeng-ing process for new Linux users, but it is hardly needed in modern distributions and is not a method specific to Linux.
• Samples of graphical desktop environments • Cinnamon
• Common Desktop Environment(CDE)
• Enlightenment
• GNOME Shell(GNOME 3)
• KDE Plasma(KDE 4)
• LXDE • MATE(GNOME 2) • Pantheon • Sugar • Trinity(KDE 3) • Unity • Xfce
5.2 Netbooks
Linux distributions have also become popular in the netbook market, with many devices such as theASUS Eee PCandAcer Aspire Oneshipping with customized Linux distributions installed.[82]
In 2009, Google announced itsGoogle Chrome OS, a minimal Linux based operating system which application consists only of the Google Chrome browser, a file man-ager and a media player.[83] Thenetbooksthat shipped with the operating system, termedChromebooks, started appearing in the market in June 2011.[84]
5.3 Servers, mainframes and
supercom-puters
Web server
Linux kernel Hardware Environment: CCC
Networking hardware CPU & RAM SATA SAS RAID iSCSI NAS Internet kmod-fs-ext4 kmod-fs-btrfs Lustre ... Responses low latency Attacks stave off & Requests serve Netfilter NIC device driver Process Scheduler Botnets DDoS-Attacks Competitors
compete for customers
Crackers
Botnets for DDoS-attacks cracking attempts ... Customers want attendance Storage CGI scripting Database Network scheduler Linux network stack
AppArmor SELinux Smack TOMOYO MariaDB MySQL Drizzle Perl PHP Python Apache Cherokee Lighttpd Nginx Squid Polipo Traffic server Web cache
Broad overview of theLAMP software bundle, displayed here together withSquid. A high-performance and high-availability web server solution providing security in a hostile environment.
Linux distributionshave long been used asserver oper-ating systems, and have risen to prominence in that area; Netcraftreported in September 2006, that eight of the ten most reliable internet hosting companies ran Linux distri-butions on theirweb servers.[85]Since June 2008, Linux distributions represented five of the top ten, FreeBSD three of ten, andMicrosofttwo of ten;[86] since Febru-ary 2010, Linux distributions represented six of the top ten, FreeBSD two of ten, and Microsoft one of ten.[87] Linux distributions are the cornerstone of the LAMP server-software combination (Linux, Apache,
5.5 Embedded devices 9
MariaDB/MySQL, Perl/PHP/Python) which has achieved popularity among developers, and which is one of the more common platforms for website hosting.[88] Linux distributions have become increasingly popular on mainframesin the last decade partly due to pricing and the open-source model.[16]In December 2009, computer giantIBMreported that it would predominantly market and sell mainframe-based Enterprise Linux Server.[89] Linux distributions are also commonly used asoperating systems for supercomputers; in the decade since Earth Simulatorsupercomputer, all the fastest supercomputers have used Linux. As of November 2014, 97% of the world’s500 fastest supercomputersrun some variant of Linux,[90]including the top 80.[91]
5.4
Smart devices
Android smartphones
Several operating systems for smart devices, such as smartphones,tablet computers,smart TVs, andin-vehicle infotainment(IVI) systems, are based on Linux. Major platforms for such systems includeAndroid,Firefox OS, MerandTizen.
Android has become the dominant mobile operating sys-tem forsmartphones, during the second quarter of 2013, 79.3% of smartphones sold worldwide used Android.[92] Android is also a popular operating system for tablets, and Android smart TVs and in-vehicle infotainment systems have also appeared in the market.
Cell phones and PDAs running Linux on open-source platforms became more common from 2007; examples include theNokia N810,Openmoko'sNeo1973, and the Motorola ROKR E8. Continuing the trend,Palm(later acquired byHP) produced a new Linux-derived operat-ing system,webOS, which is built into its line ofPalm Presmartphones.
Nokia'sMaemo, one of the earliest mobile operating sys-tems, was based onDebian.[93]It was later merged with Intel'sMoblin, another Linux-based operating system, to formMeeGo.[94] The project was later terminated in
fa-vor of Tizen, an operating system targeted at mobile de-vices as well asin-vehicle infotainment (IVI). Tizen is a project withinThe Linux Foundation. SeveralSamsung products are already running Tizen,Samsung Gear 2 be-ing the most significant example.[95] Samsung Z smart-phones will use Tizen instead of Android.[96]
As a result of MeeGo’s termination, the Mer project forked the MeeGo codebase to create a basis for mobile-oriented operating systems.[97] In July 2012, Jolla an-nouncedSailfish OS, their own mobile operating system built upon Mer technology.
Mozilla’s Firefox OS consists of the Linux kernel, a hardware abstraction layer, aweb standardsbased run-time environment and user interface, and an integrated web browser.[98]
Canonical has releasedUbuntu Touch, its own mobile operating system that aims to bring convergence to the user experience on the operating system and its desk-top counterpart,Ubuntu. The operating system also pro-vides a full Ubuntu desktop when connected to an exter-nal monitor.[99]
5.5 Embedded devices
See also:Embedded LinuxandLinux devices
Due to its low cost and ease of customization, Linux
TheJolla Phonehas the Linux-basedSailfish OS
is often used in embedded systems. In the non-mobile telecommunications equipment sector, the ma-jority ofcustomer-premises equipment(CPE) hardware runs some Linux-based operating system. OpenWrtis a community driven example upon which many of the OEM firmwares are based.
For example, the popular TiVo digital video recorder also uses a customized Linux,[101]as do several network firewallsandroutersfrom such makers asCisco/Linksys. The Korg OASYS, the Korg KRONOS, the Yamaha Motif XS/Motif XF music workstations,[102] Yamaha S90XS/S70XS, Yamaha MOX6/MOX8 synthesizers, Yamaha Motif-Rack XS tone generator module, and Roland RD-700GXdigital pianoalso run Linux. Linux
10 5 USES
In-car entertainmentsystem of the Tesla Model Sis based on
Ubuntu[100]
Nokia X, a smartphone that runs Linux kernel
is also used instage lightingcontrol systems, such as the WholeHogIII console.[103]
5.6 Gaming
Main article:Linux gaming
There had been several games that run on traditional desktop Linux, and many of which originally written for desktop OS. However, due to most game developers not paying attention to such a small market as desktop Linux, only a few prominent games have been available for desk-top Linux. On the other hand, as a popular mobile plat-form, Android has gained much developer interest and there are many games available for Android.
On 14 February 2013, Valve released a Linux ver-sion ofSteam, a popular game distribution platform on PC.[104] Many Steam games were ported to Linux.[105] On 13 December 2013, Valve releasedSteamOS, a gam-ing oriented OS based on Debian, forbeta testing, and has plans to ship Steam Machines as a gaming and entertainment platform.[106] Valve has also developed VOGL, anOpenGLdebugger intended to aid video game development,[107]as well as porting itsSourcegame en-gine to desktop Linux.[108]As a result of Valve’s effort, several prominent games such asDotA 2,Team Fortress 2, Portal,Portal 2and Left 4 Dead 2are now natively available on desktop Linux.
On 31 July 2013,NvidiareleasedShieldas an attempt to use Android as a specialized gaming platform.[109]
5.7 Specialized uses
Due to the flexibility, customizability and free and open-source nature of Linux, it becomes possible to highly tune Linux for a specific purpose. There are two main meth-ods for creating a specialized Linux distribution: building from scratch or from a general-purpose distribution as a base. The distributions often used for this purpose in-cludeDebian,Fedora,Ubuntu(which is itself based on Debian),Arch Linux,Gentoo, andSlackware. In con-trast, Linux distributions built from scratch do not have general-purpose bases; instead, they focus on theJeOS philosophy by including only necessary components and avoidingresourceoverhead caused by components con-sidered redundant in the distribution’s use cases.
5.7.1 Home theater PC
Ahome theater PC(HTPC) is a PC that is mainly used as an entertainment system, especially aHome theater sys-tem. It is normally connected to a television, and often an additional audio system.
OpenELEC, a Linux distribution that incorporates the media center softwareKodi, is an OS tuned specifically for an HTPC. Having been built from the ground up ad-hering to the JeOS principle, the OS is very lightweight and very suitable for the confined usage range of an
11
HTPC.
There are also special editions of Linux distributions that include theMythTVmedia center software, such as Mythbuntu, a special edition of Ubuntu.
5.7.2 Digital security
Kali Linuxis a Debian-based Linux distribution designed fordigital forensicsandpenetration testing. It comes pre-installed with several software applications for penetra-tion testing and identifyingsecurity exploits.[110]
5.7.3 System rescue
LinuxLive CD sessions have long been used as a tool for recovering data from a broken computer system and for repairing the system. Building upon that idea, sev-eral Linux distributions tailored for this purpose have emerged, most of which useGPartedas a partition editor, with additional data recovery and system repair software:
• GParted Live– a Debian-based distribution devel-oped by the GParted project.
• Parted Magic– a commercial Linux distribution.
• SystemRescueCD – a Gentoo-based distribution with support for editing Windowsregistry.
5.7.4 In space
SpaceX uses multiple redundant flight computers in a fault-tolerant designin theFalcon 9rocket. Each Merlin engine is controlled by threevotingcomputers, with two physical processors per computer that constantly check each other’s operation. Linux is not inherently fault-tolerant (no operating system is, as it is a function of the whole system including the hardware), but the flight com-puter software makes it so for its purpose.[111]For flex-ibility, commercial off-the-shelfparts and system-wide “radiation-tolerant” design are used instead ofradiation hardenedparts.[111]As of June 2015, SpaceX has made 19 launches of the Falcon 9 since 2010, out of which 18 have successfully delivered their primary payloads toEarth orbit, including some support missions for the International Space Station.
In addition, Windows was used as an operating system on non-mission critical systems— laptops used on board the space station, for example— but it has been replaced with Linux; the first Linux-powered humanoid robot is also undergoing in-flight testing.[112]
TheJet Propulsion Laboratoryhas used Linux for a num-ber of years “to help with projects relating to the con-struction of unmanned space flight and deep space explo-ration";NASAuses Linux in robotics in the Mars rover, andUbuntuLinux to “save data from satellites”.[113]
5.7.5 Teaching
Linux distributions have been created to provide hands-on experience with coding and source code to students, on devices such as theRaspberry Pi. In addition to pro-ducing a practical device, the intention is to show students “how things work under the hood”.
6 Market share and uptake
Main article:Linux adoptionSee also:Usage share of operating systems
Many quantitative studies of free/open-source software focus on topics including market share and reliability, with numerous studies specifically examining Linux.[114] The Linux market is growing rapidly, and the revenue of servers, desktops, and packaged software running Linux was expected to exceed $35.7 billion by 2008.[115] An-alysts and proponents attribute the relative success of Linux to its security, reliability, low cost, and freedom fromvendor lock-in.[116][117]
Desktops and laptops According toweb server statis-tics, as of March 2015, the estimated market share of Linux ondesktop computersis around 1.5%. In comparison,Microsoft Windowshas a market share of around 91.5%, while Mac OS covers around 7%.[17]
Web servers W3Cook publishes stats that use the top
one million Alexa domains,[118] which as of May 2015 estimate that 96.55% of web servers run Linux, 1.73% run Windows, and 1.72% run FreeBSD.[119]W3Techs publishes stats that use the top ten million Alexa domains, which is updated ev-ery month[120] and as of May 2015 estimates that 32.6% of web servers run Windows, with the rest being Linux or Unix.[121]IDC's Q1 2007 report in-dicated that Linux held 12.7% of the overall server market at that time;[122]this estimate was based on the number of Linux servers sold by various compa-nies, and did not include server hardware purchased separately that had Linux installed on it later. In September 2008, Microsoft’s CEO Steve Ballmer stated that 60% of web servers ran Linux, versus 40% that ranWindows Server.[123]
Mobile devices Android, which is based on the Linux
kernel, has become the dominant operating system for smartphones. During the second quarter of 2013, 79.3% of smartphones sold worldwide used Android.[92]Android is also a popular operating sys-tem for tablets, being responsible for more than 60% of tablet sales as of 2013.[124] According to web server statistics, as of December 2014 Android has a
12 7 COPYRIGHT, TRADEMARK, AND NAMING
market share of about 46%, withiOSholding 45%, and the remaining 9% attributed to various niche platforms.[125]
Film production For years Linux has been the
plat-form of choice in the film industry. The first major film produced on Linux servers was 1997’s Titanic.[126][127] Since then major studios includ-ing DreamWorks Animation,Pixar,Weta Digital, and Industrial Light & Magic have migrated to Linux.[128][129][130] According to the Linux Movies Group, more than 95% of the servers and desktops at large animation and visual effects companies use Linux.[131]
Use in government Linux distributions have also gained popularity with various local and national governments. The federal government of Brazil is well known for its support for Linux.[132][133] News of the Russian military creating its own Linux distribution has also surfaced, and has come to fruition as the G.H.ost Project.[134] The Indian state ofKeralahas gone to the extent of mandating that all state high schools run Linux on their computers.[135][136] China uses Linux exclusively as the operating system for itsLoongsonprocessor family to achieve technology independence.[137] In Spain, some regions have developed their own Linux distributions, which are widely used in education and official institutions, likegnuLinExin Extremadura andGuadalinexin Andalusia. France and Germany have also taken steps toward the adoption of Linux.[138]
7
Copyright, trademark, and
nam-ing
See also: GNU/Linux naming controversy and SCO-Linux controversies
Linux kernel islicensedunder theGNU General Public License(GPL), version 2. The GPL requires that any-one who distributes software based on source code under this license, must make the originating source code (and any modifications) available to the recipient under the same terms.[139]Other key components of a typical Linux distribution are also mainly licensed under the GPL, but they may use other licenses; many libraries use theGNU Lesser General Public License(LGPL), a more permis-sive variant of the GPL, and theX.orgimplementation of theX Window Systemuses theMIT License.
Torvalds states that the Linux kernel will not move from version 2 of the GPL to version 3.[140][141]He specifically dislikes some provisions in the new license which prohibit the use of the software indigital rights management.[142]
It would also be impractical to obtain permission from all the copyright holders, who number in the thousands.[143] A 2001 study ofRed Hat Linux7.1 found that this distri-bution contained 30 millionsource lines of code.[144] Us-ing theConstructive 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 conventionalproprietary means, it would have cost about $1.48 billion (2015 US dollars) to develop in the United States.[144]Most of the source code (71%) was written in the C programming language, but many other languages were used, includ-ingC++,Lisp,assembly language,Perl,Python,Fortran, and variousshell scriptinglanguages. 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.[144]
In a later study, the same analysis was performed for Debian version 4.0 (etch, which was released in 2007).[145]This distribution contained close to 283 mil-lion source lines of code, and the study estimated that it would have required about seventy three thousand man-years and cost US$8.16 billion (in 2015 dollars) to de-velop by conventional means.
The name “Linux” is also used for a laundry detergent made by Swiss company Rösch.
In the United States, the name Linux is a trademark reg-istered to Linus Torvalds.[3] Initially, nobody registered it, but on 15 August 1994, William R. Della Croce, Jr. filed for the trademark Linux, and then demanded royal-ties from Linux distributors. In 1996, Torvalds and some affected organizations sued him to have the trademark as-signed to Torvalds, and, in 1997, the case was settled.[146] The licensing of the trademark has since been handled by theLinux Mark Institute. Torvalds has stated that he trademarked the name only to prevent someone else from using it. LMI originally charged a nominal sublicensing fee for use of the Linux name as part of trademarks,[147] but later changed this in favor of offering a free, perpetual worldwide sublicense.[148]
13
name when referring to the operating system as a whole, because it considers Linux to be avariantof the GNU operating system, initiated in 1983 byRichard Stallman, president of the Free Software Foundation.[11][12] A minority of public figures and software projects other than Stallman and the Free Software Foundation, notably Debian(which had been sponsored by the Free Software Foundation up to 1996[149]), also use GNU/Linux when referring to the operating system as a whole.[101][150][151] Most media and common usage, however, refers to this family of operating systems simply as Linux, as do many large Linux distributions (for example,SUSE Linuxand Red Hat). As of May 2011, about 8% to 13% of a mod-ern Linux distribution is made of GNU components (the range depending on whetherGNOMEis considered part of GNU), as determined by countinglines of source code making up Ubuntu’s “Natty” release; meanwhile, about 9% is taken by the Linux kernel.[152]
8
See also
• Comparison of Linux distributions
• Comparison of open source and closed source
• Comparison of operating systems
• Comparison of X Window System desktop environ-ments
• Criticism of Linux
• Linux Documentation Project
• Linux Foundation
• List of Linux distributions
• List of games released on Linux
• List of operating systems
• Loadable kernel module
• Linus Torvalds § Possible NSA approach
• Usage share of operating systems
9
Notes
[1] “Linux” trademark is owned byLinus Torvalds[3]and ad-ministered by theLinux Mark Institute.
10
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[4] “Re: How to pronounce Linux?". Newsgroup:
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