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103-424: Goto is a statement found in many computer programming languages. Goto may also refer to: Goto The structured program theorem proved that the goto statement is not necessary to write programs that can be expressed as flow charts ; some combination of the three programming constructs of sequence, selection/choice, and repetition/iteration are sufficient for any computation that can be performed by

206-437: A Turing machine , with the caveat that code duplication and additional variables may need to be introduced. The use of goto was formerly common, but since the advent of structured programming in the 1960s and 1970s, its use has declined significantly. It remains in use in certain common usage patterns , but alternatives are generally used if available. In the past, there was considerable debate in academia and industry on

309-472: A high-level language implementation of Unix made its porting to different computer platforms easier. Due to an earlier antitrust case forbidding it from entering the computer business, AT&T licensed the operating system's source code as a trade secret to anyone who asked. As a result, Unix grew quickly and became widely adopted by academic institutions and businesses. In 1984, AT&T divested itself of its regional operating companies , and

412-424: A minimalist functionality, while more elaborate window managers such as FVWM , Enlightenment , or Window Maker provide 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 as Mutter (GNOME), KWin (KDE), or Xfwm (xfce), although users may choose to use

515-505: A solution stack such as LAMP . The source code of Linux may be used, modified, and distributed commercially or non-commercially by anyone under the terms of its respective licenses, such as the GNU General Public License (GPL). The license means creating novel distributions is permitted by anyone and is easier than it would be for an operating system such as MacOS or Microsoft Windows . The Linux kernel, for example,

618-527: A GOTO statement that unwinds the stack for an out of block transfer and does not permit a transfer into a block from outside of it. Other languages may have their own separate keywords for explicit fallthroughs, which can be considered a version of goto restricted to this specific purpose. For example, Go uses the fallthrough keyword and doesn't allow implicit fallthrough at all, while Perl 5 uses next for explicit fallthrough by default, but also allows setting implicit fallthrough as default behavior for

721-470: A branch. The value of a label variable includes the address of a stack frame, and a goto out of block pops the stack. A simpler way to get an equivalent result is using a label constant array that doesn't even need an explicit declaration of a LABEL type variable: In a DOS batch file , Goto directs execution to a label that begins with a colon. The target of the Goto can be a variable. Many languages support

824-466: A competing OS, agrees that "Linux wasn't designed, it evolved", but considers this to be a limitation, proposing that some features, especially those related to security, cannot be evolved into, "this is not a biological system at the end of the day, it's a software system." A Linux-based system is a modular Unix-like operating system, deriving much of its basic design from principles established in Unix during

927-971: A different window manager if preferred. Wayland is a display server protocol intended as a replacement for the X11 protocol; as of 2022 , it has received relatively wide adoption. Unlike X11, Wayland does not need an external window manager and compositing manager. Therefore, a Wayland compositor takes the role of the display server, window manager, and compositing 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. Enlightenment has already been successfully ported since version 19. Additionally, many window managers have been made for Wayland, such as Sway or Hyprland, as well as other graphical utilities such as Waybar or Rofi. Linux currently has two modern kernel-userspace APIs for handling video input devices: V4L2 API for video streams and radio, and DVB API for digital TV reception. Due to

1030-430: A function can be extraordinarily inefficient in some languages; a prime example is Objective-C , where a goto is a much faster alternative. Another use of goto statements is to modify poorly factored legacy code , where avoiding a goto would require extensive refactoring or code duplication . For example, given a large function where only certain code is of interest, a goto statement allows one to jump to or from only

1133-457: A label outside of the current scope, and respects object disposal and finally constructs, making it significantly less powerful and dangerous than the goto keyword in other programming languages. It also makes case and default statements labels, whose scope is the enclosing switch statement ; goto case or goto default is often used as an explicit replacement for implicit fallthrough, which C# disallows. The PL/I programing language has

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1236-563: A language where procedure calls are ubiquitous, this form of optimization considerably reduces the cost of a procedure call compared to the GOTO used in other languages. Steele argued that poorly implemented procedure calls had led to an artificial perception that the GOTO was cheap compared to the procedure call. Steele further argued that "in general procedure calls may be usefully thought of as GOTO statements which also pass parameters, and can be uniformly coded as machine code JUMP instructions", with

1339-541: A module. Most languages that have goto statements call it that, but in the early days of computing, other names were used. For example, in MAD the TRANSFER TO statement was used. APL uses a right pointing arrow, → for goto. C has goto, and it is commonly used in various idioms, as discussed above. Functional programming languages such as Scheme generally do not have goto, instead using continuations. Linux This

1442-704: A more radical relaxation of structured programming, allowing not only multiple exit points (as in returns in non-tail position), but also multiple entry points, similar to goto statements. Coroutines are more restricted than goto, as they can only resume a currently running coroutine at specified points – continuing after a yield – rather than jumping to an arbitrary point in the code. A limited form of coroutines are generators , which are sufficient for some purposes. Even more limited are closures – subroutines which maintain state (via static variables ), but not execution position. A combination of state variables and structured control, notably an overall switch statement, can allow

1545-555: A paper delivered to the ACM conference in Seattle in 1977, Guy L. Steele summarized the debate over the GOTO and structured programming, and observed that procedure calls in the tail position of a procedure can be most optimally treated as a direct transfer of control to the called procedure, typically eliminating unnecessary stack manipulation operations. Since such "tail calls" are very common in Lisp ,

1648-404: A place in server installations such as the popular LAMP application stack. The use of Linux distributions in home and enterprise desktops has been growing. Linux distributions have also become popular in the netbook market, with many devices shipping with customized Linux distributions installed, and Google releasing their own ChromeOS designed for netbooks. Linux's greatest success in

1751-498: A popular CLI shell. The graphical user interface (or GUI) used by most Linux systems is built on top of an implementation of the X Window System . More recently, the Linux community has sought to advance to Wayland as the new display server protocol, in place of X11. Many other open-source software projects contribute to Linux systems. Installed components of a Linux system include the following: The user interface , also known as

1854-449: A selected menu option, for example). PL/I label variables achieve the effect of computed or assigned GOTO s. Up to the 1985 ANSI COBOL standard had the ALTER statement which could be used to change the destination of an existing GO TO, which had to be in a paragraph by itself. The feature, which allowed polymorphism , was frequently condemned and seldom used. In Perl , there is

1957-481: A significant business around Linux distributions. The free software licenses , on which the various software packages of a distribution built on the Linux kernel are based, explicitly accommodate and encourage commercialization; the relationship between a Linux distribution 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

2060-493: 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 to sell hardware. This used to be the norm in the computer industry, with operating systems such as CP/M , Apple DOS , and versions of the classic Mac OS before 7.6 freely copyable (but not modifiable). As computer hardware standardized throughout

2163-555: A statement label (line number) which is stored in (assigned to) an integer variable. Jumping to an integer variable that had not been ASSIGNed to was unfortunately possible, and was a major source of bugs involving assigned gotos. The Fortran assign statement only allows a constant (existing) line number to be assigned to the integer variable. However, some compilers allowed accidentally treating this variable as an integer thereafter, for example increment it, resulting in unspecified behavior at goto time. The following code demonstrates

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2266-422: A structured unit prematurely, and a combinatorial explosion with quite complex program state data to handle all possible conditions. Two solutions have been generally adopted: a way to exit a structured unit prematurely, and more generally exceptions – in both cases these go up the structure, returning control to enclosing blocks or functions, but do not jump to arbitrary code locations. These are analogous to

2369-453: A subroutine to resume execution at an arbitrary point on subsequent calls, and is a structured alternative to goto statements in the absence of coroutines; this is a common idiom in C, for example. A continuation is similar to a GOTO in that it transfers control from an arbitrary point in the program to a previously marked point. A continuation is more flexible than GOTO in those languages that support it, because it can transfer control out of

2472-438: A switch statement, or to centralize cleanup tasks in a function with several error returns. (...) Blindly avoiding certain constructs or following rules without understanding them can lead to just as many problems as the rules were supposed to avert. Furthermore, many opinions on programming style are just that: opinions. They may be strongly argued and strongly felt, they may be backed up by solid-seeming evidence and arguments, but

2575-972: A system's software from one central location. A distribution 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 with Fedora , and SUSE does with openSUSE . In many cities and regions, local associations known as Linux User Groups (LUGs) seek to promote their preferred distribution and by extension free software. They hold meetings and provide free demonstrations, training, technical support, and operating system installation to new users. Many Internet communities also provide support to Linux users and developers. Most distributions and free software / open-source projects have IRC chatrooms or newsgroups . Online forums are another means of support, with notable examples being Unix & Linux Stack Exchange , LinuxQuestions.org and

2678-401: A useful language feature, improving program speed, size and code clarity, but only when used in a sensible way by a comparably sensible programmer. According to computer science professor John Regehr , in 2013, there were about 100,000 instances of goto in the Linux kernel code. Other academics took a more extreme viewpoint and argued that even instructions like break and return from

2781-402: A user may interact with the application; however, certain extensions of the X Window System are not capable of working over the network. Several X display servers exist, with the reference implementation, X.Org Server , being the most popular. Server distributions might provide a command-line interface for developers and administrators, but provide a custom interface for end-users, designed for

2884-430: A variant of the goto statement that is not a traditional GOTO statement at all. It takes a function name and transfers control by effectively substituting one function call for another (a tail call ): the new function will not return to the GOTO, but instead to the place from which the original function was called. There are several programming languages that do not support GOTO by default. By using GOTO emulation, it

2987-453: 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. Many developers of open-source software agree that the Linux kernel was not designed but rather evolved through natural selection . Torvalds considers that although

3090-465: Is goto (20,30,40) i . The equivalent construct in C is the switch statement , and in newer Fortran a SELECT CASE construct is the recommended syntactical alternative. BASIC had a 'On GoTo' statement that achieved the same goal, but in Visual Basic this construct is no longer supported. In versions prior to Fortran 95, Fortran also had an assigned goto variant that transfers control to

3193-585: Is "infinitely abusable", but also suggest that it could be used for end-of-function error handlers and for multi-level breaks from loops. These two patterns can be found in numerous subsequent books on C by other authors; a 2007 introductory textbook notes that the error handling pattern is a way to work around the "lack of built-in exception handling within the C language". Other programmers, including Linux kernel designer and coder Linus Torvalds or software engineer and book author Steve McConnell , also object to Dijkstra's point of view, stating that GOTOs can be

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3296-457: Is a 1968 letter by Edsger Dijkstra called " Go-to statement considered harmful ". In that letter, Dijkstra argued that unrestricted GOTO statements should be abolished from higher-level languages because they complicated the task of analyzing and verifying the correctness of programs (particularly those involving loops). The letter itself sparked a debate, including a " 'GOTO Considered Harmful' Considered Harmful" letter sent to Communications of

3399-500: Is an accepted version of this page Linux ( / ˈ l ɪ n ʊ k s / , LIN -uuks ) is a family of open-source Unix-like operating systems based on the Linux kernel , an operating system kernel first released on September 17, 1991, by Linus Torvalds . Linux is typically packaged as a Linux distribution (distro), which includes the kernel and supporting system software and libraries — many of which are provided by

3502-446: Is less relevant or completely absent. One of the main alternatives is message passing , which is of particular importance in concurrent computing , interprocess communication , and object oriented programming . In these cases, the individual components do not have arbitrary transfer of control, but the overall control may be scheduled in complex ways, such as via preemption . The influential languages Simula and Smalltalk were among

3605-562: Is licensed under the GPLv2, with an exception for system calls that allows code that calls the kernel via system calls not to be licensed under the GPL. Because of the dominance of Linux-based Android on smartphones , Linux, including Android, has the largest installed base of all general-purpose operating systems as of May 2022 . Linux is, as of March 2024 , used by around 4 percent of desktop computers . The Chromebook , which runs

3708-437: Is mandatory. Although Steele's paper did not introduce much that was new to computer science, at least as it was practised at MIT, it brought to light the scope for procedure call optimization, which made the modularity-promoting qualities of procedures into a more credible alternative to the then-common coding habits of large monolithic procedures with complex internal control structures and extensive state data. In particular,

3811-482: Is possible to express the same logic without gotos, the equivalent code will be longer and often more difficult to understand). In other languages, there are structured alternatives, notably exceptions and tail calls. Situations in which goto is often useful include: These uses are relatively common in C, but much less common in C++ or other languages with higher-level features. However, throwing and catching an exception inside

3914-451: Is referred to as a computed goto in documentation of the C compilers that support it; its semantics are a superset of Fortran's assigned goto, because it allows arbitrary pointer expressions as the goto target, while Fortran's assigned goto doesn't allow arbitrary expressions as jump target. As with the standard goto in C, the GNU C extension allows the target of the computed goto to reside only in

4017-462: Is still possible to use GOTO in these programming languages, albeit with some restrictions. One can emulate GOTO in Java, JavaScript, and Python. PL/I has the data type LABEL , which can be used to implement both the "assigned goto" and the "computed goto." PL/I allows branches out of the current block. A calling procedure can pass a label as an argument to a called procedure which can then exit with

4120-403: 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 by far the most widely used. Some free and open-source software licenses 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,

4223-577: Is the Bourne-Again Shell (bash), originally developed for the GNU Project, other shells such as Zsh are also used. Most low-level Linux components, including various parts of the userland , use the CLI exclusively. The CLI is particularly suited for automation of repetitive or delayed tasks and provides very simple inter-process communication . On desktop systems, the most popular user interfaces are

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4326-468: Is typically built into the firmware and is highly tailored to the system. This includes routers , automation controls, smart home devices , video game consoles , televisions (Samsung and LG smart TVs ), automobiles (Tesla, Audi, Mercedes-Benz, Hyundai, and Toyota), and spacecraft ( Falcon 9 rocket, Dragon crew capsule, and the Ingenuity Mars helicopter). The Unix operating system

4429-415: Is used on a wide variety of devices including PCs, workstations , mainframes and embedded systems . Linux is the predominant operating system for servers and is also used on all of the world's 500 fastest supercomputers . When combined with Android , which is Linux-based and designed for smartphones , they have the largest installed base of all general-purpose operating systems . The Linux kernel

4532-637: The goto statement, and many do not. In Java , goto is a reserved word , but is unusable, although compiled .class files generate GOTOs and LABELs. Python does not have support for goto, although there are several joke modules that provide it. There is no goto statement in Seed7 and hidden gotos like break- and continue-statements are also omitted. In PHP there was no native support for goto until version 5.3 (libraries were available to emulate its functionality). C# and Visual Basic .NET both support goto . However, it does not allow jumping to

4635-617: The ACM (CACM) in March 1987, as well as further replies by other people, including Dijkstra's On a Somewhat Disappointing Correspondence . An alternative viewpoint is presented in Donald Knuth 's Structured Programming with go to Statements , which analyzes many common programming tasks and finds that in some of them GOTO is the optimal language construct to use. In The C Programming Language , Brian Kernighan and Dennis Ritchie warn that goto

4738-487: The Free Software Foundation and wrote the GNU General 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 , a command-line shell , and a windowing system ) were completed, although low-level elements such as device drivers , daemons , and the kernel , called GNU Hurd , were stalled and incomplete. Minix

4841-654: The GNU Project — to create a complete operating system. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses and recommends the name " GNU/Linux " to emphasize the use and importance of GNU software in many distributions, causing some controversy . Thousands of distributions exist, many based directly or indirectly on other distributions; popular Linux distributions include Debian , Fedora Linux , Arch Linux , and Ubuntu , while commercial distributions include Red Hat Enterprise Linux and SUSE Linux Enterprise . Other than

4944-736: The GNU toolchain , which includes the GNU Compiler Collection (GCC) and the GNU Build System . Amongst others, GCC provides compilers for Ada , C , C++ , Go and Fortran . Many programming languages have a cross-platform reference implementation that supports Linux, for example PHP , Perl , Ruby , Python , Java , Go , Rust and Haskell . First released in 2003, the LLVM project provides an alternative cross-platform open-source compiler for many languages. Proprietary compilers for Linux include

5047-470: The GUI shells , packaged together with extensive Desktop environments , such as KDE Plasma , GNOME , MATE , Cinnamon , LXDE , Pantheon , and Xfce , though a variety of additional user interfaces exist. Most popular user interfaces are based on the X Window System, often simply called "X". It provides network transparency and permits a graphical application running on one system to be displayed on another where

5150-476: The shell , is either a command-line interface (CLI), a graphical user interface (GUI), or controls attached to the associated hardware, which is common for embedded systems. For desktop systems, the default user interface is usually graphical, although the CLI is commonly available through terminal emulator windows or on a separate virtual console . CLI shells are text-based user interfaces, which use text for both input and output. The dominant shell used in Linux

5253-401: The "computed goto" in which the instruction to jump to is determined dynamically (conditionally). Under certain conditions it is possible to eliminate local goto statements of legacy programs by replacing them with multilevel loop exit statements. In practice, a strict adherence to the basic three-structure template of structured programming yields highly nested code, due to inability to exit

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5356-399: The 1970s and 1980s. Such a system uses a monolithic kernel , the Linux kernel, which handles process control, networking, access to the peripherals , and file systems . Device drivers are either integrated directly with the kernel or added as modules that are loaded while the system is running. The GNU userland is a key part of most systems based on the Linux kernel, with Android being

5459-451: The 1980s, it became more difficult for hardware manufacturers to profit from this tactic, as the OS would run on any manufacturer's computer that shared the same architecture. Most programming languages support Linux either directly or through third-party community based ports . The original development tools used for building both Linux applications and operating system programs are found within

5562-663: The GNU General Public License (GPL), is a form of copyleft and is used for the Linux kernel and many of the components from the GNU Project. Linux-based distributions are intended by developers for interoperability with other operating systems and established computing standards. Linux systems adhere to POSIX, SUS , LSB , ISO , and ANSI standards where possible, although to date only one Linux distribution has been POSIX.1 certified, Linux-FT. Free software projects, although developed through collaboration , are often produced independently of each other. The fact that

5665-443: The GOTO statement – see language support – though most provide some means of breaking out of a selection, or either breaking out of or moving on to the next step of an iteration. The viewpoint that disturbing the control flow in code is undesirable may be seen in the design of some programming languages, for instance Ada visually emphasizes label definitions using angle brackets . Entry 17.10 in comp.lang.c FAQ list addresses

5768-460: The Linux kernel, key components that make up a distribution may include a display server (windowing system) , a package manager , a bootloader and the Bash shell . Linux is one of the most prominent examples of free and open-source software collaboration. While originally developed for x86 based personal computers , it has since been ported to more platforms than any other operating system, and

5871-647: The Linux kernel-based ChromeOS , dominates the US K–12 education market and represents nearly 20 percent of sub-$ 300 notebook sales in the US. Linux is the leading operating system on servers (over 96.4% of the top one million web servers' operating systems are Linux), leads other big iron systems such as mainframe computers , and is used on all of the world's 500 fastest supercomputers (as of November 2017 , having gradually displaced all competitors). Linux also runs on embedded systems , i.e., devices whose operating system

5974-605: The Linux kernel. On July 3, 1991, to implement Unix system calls , Linus Torvalds attempted unsuccessfully to obtain a digital copy of the POSIX standards documentation with a request to the comp.os.minix newsgroup . After not finding the POSIX documentation, Torvalds initially resorted to determining system calls from SunOS documentation owned by the university for use in operating its Sun Microsystems server. He also learned some system calls from Tanenbaum's Minix text. Torvalds began

6077-629: The ability to structure programs using well-nested executions of routines drawn from a library. This would not have been possible using only goto , since the target code, being drawn from the library, would not know where to jump back to. Later, high-level languages such as Pascal were designed around support for structured programming , which generalized from subroutines (also known as procedures or functions) towards further control structures such as: These new language mechanisms replaced equivalent flows which previously would have been written using goto s and if s. Multi-way branching replaces

6180-466: The beginning, it was rather casually hacked on by huge numbers of volunteers coordinating only through the Internet. Quality was maintained not by rigid standards or autocracy but by the naively simple strategy of releasing every week and getting feedback from hundreds of users within days, creating a sort of rapid Darwinian selection on the mutations introduced by developers." Bryan Cantrill , an engineer of

6283-458: The behavior of the goto i when line i is unspecified: Several C compilers implement two non-standard C/C++ extensions relating to gotos originally introduced by gcc . The GNU extension allows the address of a label inside the current function to be obtained as a void* using the unary, prefix label value operator && . The goto instruction is also extended to allow jumping to an arbitrary void* expression. This C extension

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6386-447: The complexity and diversity of different devices, and due to the large number of formats and standards handled by those APIs, this infrastructure needs to evolve to better fit other devices. Also, a good userspace device library is the key to the success of having userspace applications to be able to work with all formats supported by those devices. The primary difference between Linux and many other popular contemporary operating systems

6489-408: The construction was more likely to obscure a program than to improve it because its application requires the introduction of additional local variables. It did, however, spark a prominent debate among computer scientists, educators, language designers and application programmers that saw a slow but steady shift away from the formerly ubiquitous use of the GOTO. Probably the most famous criticism of GOTO

6592-498: The consumer market is perhaps the mobile device market, with Android being the dominant operating system on smartphones and very popular on tablets and, more recently, on wearables . Linux gaming is also on the rise with Valve showing its support for Linux and rolling out SteamOS , its own gaming-oriented Linux distribution, which was later implemented in their Steam Deck platform. Linux distributions have also gained popularity with various local and national governments, such as

6695-532: The current context to a surrounding one. The Common Lisp GO operator also has this stack unwinding property, despite the construct being lexically scoped , as the label to be jumped to can be referenced from a closure . In Scheme , continuations can even move control from an outer context to an inner one if desired. This almost limitless control over what code is executed next makes complex control structures such as coroutines and cooperative multitasking relatively easy to write. In non-procedural paradigms, goto

6798-428: The current function, something that a GOTO cannot do in most structured programming languages. In those language implementations that maintain stack frames for storage of local variables and function arguments, executing a continuation involves adjusting the program's call stack in addition to a jump. The longjmp function of the C programming language is an example of an escape continuation that may be used to escape

6901-464: The current function. Attempting to jump outside the current function results in unspecified behavior. Some variants of BASIC also support a computed GOTO in the sense used in GNU C, i.e. in which the target can be any line number, not just one from a list. For example, in MTS BASIC one could write GOTO i*1000 to jump to the line numbered 1000 times the value of a variable i (which might represent

7004-464: The design of Unix served as a scaffolding, "Linux grew with a lot of mutations – and because the mutations were less than random, they were faster and more directed than alpha-particles in DNA ." Eric S. Raymond considers Linux's revolutionary aspects to be social, not technical: before Linux, complex software was designed carefully by small groups, but "Linux evolved in a completely different way. From nearly

7107-461: The destination of a goto statement. For example, the C programming language does not permit a jump to a label contained within another function, however jumps within a single call chain are possible using the setjmp/longjmp functions. At the pre-ALGOL meeting held in 1959, Heinz Zemanek explicitly cast doubt on the necessity of GOTO statements; at the time no one paid attention to his remark, including Edsger W. Dijkstra , who later became

7210-502: The development of 386BSD , from which NetBSD , OpenBSD and FreeBSD descended, predated that of Linux. Linus Torvalds has stated on separate occasions that if the GNU kernel or 386BSD had been available at the time (1991), he probably would not have created Linux. While attending the University of Helsinki in the fall of 1990, Torvalds enrolled in a Unix course. The course used a MicroVAX minicomputer running Ultrix , and one of

7313-527: 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. GNU applications also replaced all Minix components, because it was advantageous to use the freely available code from the GNU Project with the fledgling operating system; code licensed under the GNU GPL can be reused in other computer programs as long as they also are released under

7416-476: The development of the components of the system and free software. An analysis of the Linux kernel in 2017 showed that well over 85% of the code was developed by programmers who are being paid for their work, leaving about 8.2% to unpaid developers and 4.1% unclassified. Some of the major corporations that provide contributions include Intel , Samsung , Google , AMD , Oracle , and Facebook . Several corporations, notably Red Hat, Canonical , and SUSE have built

7519-500: The federal government of Brazil . Linus Torvalds is the lead maintainer for the Linux kernel and guides its development, while Greg Kroah-Hartman is the lead maintainer for the stable branch. Zoë Kooyman is the executive director of 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

7622-414: The first to introduce the concepts of messages and objects. By encapsulating state data, object-oriented programming reduced software complexity to interactions (messages) between objects. There are a number of different language constructs under the class of goto statements. In Fortran , a computed GOTO jumps to one of several labels in a list, based on the value of an expression. An example

7725-466: The first version of the Linux kernel on the Internet . Like GNU and 386BSD, Linux did not have any Unix code and therefore avoided any current legal issues . Desktop Linux distributions include a windowing system such as X11 or Wayland and a desktop environment such as GNOME , KDE Plasma or Xfce . Distributions intended for servers may not have a graphical user interface at all or include

7828-484: The goto statement does not necessarily lead immediately to beautiful programming: an unstructured programmer is just as capable of constructing a Byzantine tangle without using any goto's (perhaps substituting oddly-nested loops and Boolean control variables, instead). Many programmers adopt a moderate stance: goto's are usually to be avoided, but are acceptable in a few well-constrained situations, if necessary: as multi-level break statements, to coalesce common actions inside

7931-564: The iconic opponent of GOTO. The 1970s and 1980s saw a decline in the use of GOTO statements in favor of the structured programming paradigm , with GOTO criticized as leading to unmaintainable spaghetti code . Some programming style coding standards, for example the GNU Pascal Coding Standards, recommend against the use of GOTO statements. The Böhm–Jacopini proof (1966) did not settle the question of whether to adopt structured programming for software development, partly because

8034-408: The issue of GOTO use directly, stating Programming style, like writing style, is somewhat of an art and cannot be codified by inflexible rules, although discussions about style often seem to center exclusively around such rules. In the case of the goto statement, it has long been observed that unfettered use of goto's quickly leads to unmaintainable spaghetti code. However, a simple, unthinking ban on

8137-470: The machine code stack manipulation instructions "considered an optimization (rather than vice versa!)". Steele cited evidence that well optimized numerical algorithms in Lisp could execute faster than code produced by then-available commercial Fortran compilers because the cost of a procedure call in Lisp was much lower. In Scheme , a Lisp dialect developed by Steele with Gerald Jay Sussman , tail call optimization

8240-496: The merits of the use of goto statements. The primary criticism is that code that uses goto statements is harder to understand than alternative constructions. Debates over its (more limited) uses continue in academia and software industry circles. goto label The goto statement is often combined with the if statement to cause a conditional transfer of control. IF condition THEN goto label Programming languages impose different restrictions with respect to

8343-516: The mid-1990s in the supercomputing community, where organizations such as NASA started to replace their increasingly expensive machines with clusters of inexpensive commodity computers running Linux. Commercial use began when Dell and IBM , followed by Hewlett-Packard , started offering Linux support to escape Microsoft 's monopoly in the desktop operating system market. Today, Linux systems are used throughout computing, from embedded systems to virtually all supercomputers , and have secured

8446-668: The middle of loops are bad practice as they are not needed in the Böhm–Jacopini result, and thus advocated that loops should have a single exit point. For instance, Bertrand Meyer wrote in his 2009 textbook that instructions like break and continue "are just the old goto in sheep's clothing". A slightly modified form of the Böhm–Jacopini result, however, allows the avoidance of additional variables in structured programming, as long as multi-level breaks from loops are allowed. Because some languages like C don't allow multi-level breaks via their break keyword, some textbooks advise

8549-441: The notable exception. The GNU C library , an implementation of the C standard library , works as a wrapper for the system calls of the Linux kernel necessary to the kernel-userspace interface, the toolchain is a broad collection of programming tools vital to Linux development (including the compilers used to build the Linux kernel itself), and the coreutils implement many basic Unix tools . The GNU Project also develops Bash ,

8652-501: The operating 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 generally integration of the different software packages into a coherent whole. Distributions typically use a package manager such as apt , yum , zypper , pacman or portage to install, remove, and update all of

8755-426: The opposing opinions may be just as strongly felt, supported, and argued. It's usually futile to get dragged into "style wars", because on certain issues, opponents can never seem to agree, or agree to disagree, or stop arguing. While overall usage of goto has been declining, there are still situations in some languages where a goto provides the shortest and most straightforward way to express a program's logic (while it

8858-549: The programmer to use goto in such circumstances. The MISRA C 2004 standard bans goto , continue , as well as multiple return and break statements. The 2012 edition of the MISRA C standard downgraded the prohibition on goto from "required" to "advisory" status; the 2012 edition has an additional, mandatory rule that prohibits only backward, but not forward jumps with goto . FORTRAN introduced structured programming constructs in 1978, and in successive revisions

8961-540: The relatively loose semantic rules governing the allowable use of goto were tightened; the "extended range" in which a programmer could use a GOTO to leave and re-enter a still-executing DO loop was removed from the language in 1978, and by 1995 several forms of Fortran GOTO, including the Computed GOTO and the Assigned GOTO, had been deleted. Some widely used modern programming languages such as Java and Python lack

9064-449: The relevant code, without otherwise modifying the function. This usage is considered code smell , but finds occasional use. The modern notion of subroutine was invented by David Wheeler when programming the EDSAC . To implement a call and return on a machine without a subroutine call instruction, he used a special pattern of self-modifying code, known as a Wheeler jump . This resulted in

9167-455: The required texts was Operating Systems: Design and Implementation by Andrew S. Tanenbaum . This textbook included a copy of Tanenbaum's Minix operating system. It was with this course that Torvalds first became exposed to Unix. In 1991, he became curious about operating systems. Frustrated by the licensing of Minix, which at the time limited it to educational use only, he began to work on his operating system kernel, which eventually became

9270-412: The same or a compatible license. Torvalds initiated a switch from his original license, which prohibited commercial redistribution, to the GNU GPL. Developers worked to integrate GNU components with the Linux kernel, creating a fully functional and free operating system. Linus Torvalds had wanted to call his invention " Freax ", a portmanteau of "free", "freak", and "x" (as an allusion to Unix). During

9373-441: 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 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

9476-569: The start of his work on the system, some of the project's makefiles included the name "Freax" for about half a year. Initially, Torvalds considered the name "Linux" but dismissed it as too egotistical. To facilitate development, the files were uploaded to the FTP server ( ftp.funet.fi ) of FUNET in September 1991. Ari Lemmke, Torvalds' coworker at the Helsinki University of Technology (HUT) who

9579-437: The tail call optimizations discussed by Steele turned the procedure into a credible way of implementing iteration through single tail recursion (tail recursion calling the same function). Further, tail call optimization allows mutual recursion of unbounded depth, assuming tail calls – this allows transfer of control, as in finite state machines , which otherwise is generally accomplished with goto statements. Coroutines are

9682-471: The use case of the system. This custom interface is accessed through a client that resides on another system, not necessarily Linux-based. Several types of window managers exist for X11, including tiling , dynamic , stacking , and compositing . Window managers provide means to control the placement and appearance of individual application windows, and interact with the X Window System. Simpler X window managers such as dwm , ratpoison , or i3wm provide

9785-681: The use of a return statement in non-terminal position – not strictly structured, due to early exit, but a mild relaxation of the strictures of structured programming. In C, break and continue allow one to terminate a loop or continue to the next iteration , without requiring an extra while or if statement. In some languages multi-level breaks are also possible. For handling exceptional situations, specialized exception handling constructs were added, such as try / catch / finally in Java. The throw-catch exception handling mechanisms can also be easily abused to create non-transparent control structures, just like goto can be abused. In

9888-559: The various distribution-specific support and community forums, such as ones for Ubuntu , Fedora, Arch Linux , Gentoo , etc. 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. Print magazines on Linux often bundle cover disks that carry software or even complete Linux distributions. Although Linux distributions are generally available without charge, several large corporations sell, support, and contribute to

9991-429: The word "Linux" should be pronounced, he included an audio guide with the kernel source code. However, in this recording, he pronounces Linux as /ˈlinʊks/ ( LEEN -uuks ) with a short but close front unrounded vowel , instead of a near-close near-front unrounded vowel as in his newsgroup post. The adoption of Linux in production environments, rather than being used only by hobbyists, started to take off first in

10094-501: Was conceived and implemented in 1969, at AT&T 's Bell Labs , in the United States by Ken Thompson , Dennis Ritchie , Douglas McIlroy , and Joe Ossanna . First released in 1971, Unix was written entirely in assembly language , as was common practice at the time. In 1973, in a key pioneering approach, it was rewritten in the C programming language by Dennis Ritchie (except for some hardware and I/O routines). The availability of

10197-494: Was created by Andrew S. Tanenbaum , a computer science professor, and released in 1987 as a minimal Unix-like operating system targeted at students and others who wanted to learn operating system principles. Although the complete source code of Minix was freely available, the licensing terms prevented it from being free software until the licensing changed in April 2000. Although not released until 1992, due to legal complications ,

10300-510: Was designed by Linus Torvalds , following the lack of a working kernel for GNU , a Unix -compatible operating system made entirely of free software that had been undergoing development since 1983 by Richard Stallman . While a separate working Unix-compatible system called Minix was later released, its license was not entirely free at the time. The first entirely free Unix for personal computers, 386BSD , did not appear until 1992, by which time Torvalds had already built and publicly released

10403-459: Was later originally developed, it represented the first successful commercial attempt at distributing a primarily single-user microcomputer that ran a Unix operating system. With Unix increasingly "locked in" as a proprietary product, the GNU Project , started in 1983 by Richard Stallman , had the goal of creating a "complete Unix-compatible software system" composed entirely of free software . Work began in 1984. Later, in 1985, Stallman started

10506-510: 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 consulting Torvalds. Later, however, Torvalds consented to "Linux". According to a newsgroup post by Torvalds, the word "Linux" should be pronounced ( / ˈ l ɪ n ʊ k s / LIN -uuks ) with a short 'i' as in 'print' and 'u' as in 'put'. To further demonstrate how

10609-518: Was released from its obligation not to enter the computer business; freed of that obligation, Bell Labs began selling Unix as a proprietary product, where users were not legally allowed to modify it. Onyx Systems began selling early microcomputer-based Unix workstations in 1980. Later, Sun Microsystems , founded as a spin-off of a student project at Stanford University , also began selling Unix-based desktop workstations in 1982. While Sun workstations did not use commodity PC hardware, for which Linux

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