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46-456: It is a fork of the Firefox web browser with privacy-oriented changes, among which are a crowdsourced anti-tracking mechanism and an in-house search engine embedded within the browser, utilizing its own index of web pages to produce suggestions within the address bar dropdown menu rather than on separate pages. The browser's developers argued that other privacy-focused search engines may still pass

92-570: A development branch , but also a split in the developer community; as such, it is a form of schism . Grounds for forking are varying user preferences and stagnated or discontinued development of the original software. Free and open-source software is that which, by definition, may be forked from the original development team without prior permission, and without violating copyright law. However, licensed forks of proprietary software ( e.g. Unix ) also happen. The word "fork" has been used to mean "to divide in branches, go separate ways" as early as

138-448: A word processor for IBM PC compatible machines and Macintosh computers. Generally, such internal forks will concentrate on having the same look, feel, data format, and behavior between platforms so that a user familiar with one can also be productive or share documents generated on the other. This is almost always an economic decision to generate a greater market share and thus pay back the associated extra development costs created by

184-449: A Cliqz identifier. The data collection is enabled by default; users must actively opt-out if they do not wish the data to be transmitted. In 2018, Cliqz released a version of their browser for iOS called Lumen . It natively leveraged Cliqz's search engine, [ Human Web], and supported ad-blocking and other privacy features, like an optional built-in VPN with access to 25 countries. The VPN network

230-548: A branch "forks off" a version of the program. The term was in use on Usenet by 1983 for the process of creating a subgroup to move topics of discussion to. "Fork" is not known to have been used in the sense of a community schism during the origins of Lucid Emacs (now XEmacs ) (1991) or the Berkeley Software Distributions (BSDs) (1993–1994); Russ Nelson used the term "shattering" for this sort of fork in 1993, attributing it to John Gilmore . However, "fork"

276-563: A browser called Ghostery Dawn was reported to be under development. Ghostery Dawn became available for public download in October 2021. On 6 October 2017, Mozilla announced a test where approximately 1% of users downloading Firefox in Germany would receive a version with Cliqz software included. The feature provided recommendations directly in the browser's search field. Recommendations included news, weather, sports, and other websites and were based on

322-449: A copy of itself. It is an interface which is required for compliance with the POSIX and Single UNIX Specification standards. It is usually implemented as a C standard library wrapper to the fork, clone, or other system calls of the kernel . Fork is the primary method of process creation on Unix-like operating systems. In multitasking operating systems, processes (running programs) need

368-529: A fork, with examples: Distributed revision control (DVCS) tools have popularised a less emotive use of the term "fork", blurring the distinction with "branch". With a DVCS such as Mercurial or Git , the normal way to contribute to a project, is to first create a personal branch of the repository, independent of the main repository, and later seek to have your changes integrated with it. Sites such as GitHub , Bitbucket and Launchpad provide free DVCS hosting expressly supporting independent branches, such that

414-553: A process calls fork, it is deemed the parent process and the newly created process is its child. After the fork, both processes not only run the same program, but they resume execution as though both had called the system call. They can then inspect the call's return value to determine their status, child or parent, and act accordingly. One of the earliest references to a fork concept appeared in A Multiprocessor System Design by Melvin Conway , published in 1962. Conway's paper motivated

460-540: A proprietary grant in the form of a Contributor License Agreement .) Examples include macOS (based on the proprietary NeXTSTEP and the open source FreeBSD ), Cedega and CrossOver (proprietary forks of Wine , though CrossOver tracks Wine and contributes considerably), EnterpriseDB (a fork of PostgreSQL , adding Oracle compatibility features ), Supported PostgreSQL with their proprietary ESM storage system, and Netezza's proprietary highly scalable derivative of PostgreSQL. Some of these vendors contribute back changes to

506-422: A remote repository of offers, with no personally identifiable data sent to remote servers. On 15 February 2017, Cliqz International GmbH, a wholly-owned subsidiary of Cliqz GmbH, acquired the privacy-oriented browser extension Ghostery . On 29 April 2020, Cliqz announced it will shut down its browser and search engine. Subsequently, the search engine - called Tailcat - was acquired by Brave . As of March 2021,

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552-644: A replacement for the vfork interface, POSIX introduced the posix_spawn family of functions that combine the actions of fork and exec. These functions may be implemented as library routines in terms of fork , as is done in Linux, or in terms of vfork for better performance, as is done in Solaris, but the POSIX specification notes that they were "designed as kernel operations ", especially for operating systems running on constrained hardware and real-time systems . While

598-468: A way to create new processes, e.g. to run other programs. Fork and its variants are typically the only way of doing so in Unix-like systems. For a process to start the execution of a different program, it first forks to create a copy of itself. Then, the copy, called the " child process ", calls the exec system call to overlay itself with the other program: it ceases execution of its former program in favor of

644-478: Is an optimization over plain fork in full-copy environments when used with exec. In POSIX, using vfork for any purpose except as a prelude to an immediate call to a function from the exec family (and a select few other operations) gives rise to undefined behavior . As with vfork, the child borrows data structures rather than copying them. vfork is still faster than a fork that uses copy on write semantics. System V did not support this function call before System VR4

690-454: Is rather unfortunate that Linux revived this specter from the past. The BSD man page states: "This system call will be eliminated when proper system sharing mechanisms are implemented. Users should not depend on the memory sharing semantics of vfork() as it will, in that case, be made synonymous to fork(2)." Other problems with vfork include deadlocks that might occur in multithreaded programs due to interactions with dynamic linking . As

736-418: Is sometimes made when the forked software is designed to be a drop-in replacement for the original project, e.g. MariaDB for MySQL or LibreOffice for OpenOffice.org . The BSD licenses permit forks to become proprietary software, and copyleft proponents say that commercial incentives thus make proprietisation almost inevitable. (Copyleft licenses can, however, be circumvented via dual-licensing with

782-403: The fork system call to split execution into two processes. The return value of fork is recorded in a variable of type pid_t , which is the POSIX type for process identifiers (PIDs). Minus one indicates an error in fork : no new process was created, so an error message is printed. If fork was successful, then there are now two processes, both executing the main function from

828-405: The "Hello, World!" program demonstrates the mechanics of the fork system call in the C programming language. The program forks into two processes, each deciding what functionality they perform based on the return value of the fork system call. Boilerplate code such as header inclusions has been omitted. What follows is a dissection of this program. The first statement in main calls

874-431: The 14th century. In the software environment, the word evokes the fork system call, which causes a running process to split itself into two (almost) identical copies that (typically) diverge to perform different tasks. In the context of software development, "fork" was used in the sense of creating a revision control " branch " by Eric Allman as early as 1980, in the context of Source Code Control System : Creating

920-401: The 2004 edition and was replaced by posix_spawn () (which is typically implemented via vfork) in subsequent editions. When a vfork system call is issued, the parent process will be suspended until the child process has either completed execution or been replaced with a new executable image via one of the " exec " family of system calls. The child borrows the memory management unit setup from

966-502: The 4.4BSD implementation got rid of the vfork implementation, causing vfork to have the same behavior as fork, it was later reinstated in the NetBSD operating system for performance reasons. Some embedded operating systems such as uClinux omit fork and only implement vfork, because they need to operate on devices where copy-on-write is impossible to implement due to lack of a memory management unit. The Plan 9 operating system, created by

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1012-561: The Cliqz corporation including text typed in the address bar, queries to other search engines, information about visited webpages and interactions with them including mouse movement, scrolling, and amount of time spent; and the user's interactions with the user interface of the Cliqz software. Interaction data collected and sent to the Mozilla corporation includes among other things, counts of visits to search engine pages, which search engines are used, and

1058-519: The Noosphere , stated that "The most important characteristic of a fork is that it spawns competing projects that cannot later exchange code, splitting the potential developer community". He notes in the Jargon File : Forking is considered a Bad Thing—not merely because it implies a lot of wasted effort in the future, but because forks tend to be accompanied by a great deal of strife and acrimony between

1104-417: The POSIX _exit function must be used here instead of the C standard exit function.) The other process, the parent, receives from fork the process identifier of the child, which is always a positive number. The parent process passes this identifier to the waitpid system call to suspend execution until the child has exited. When this has happened, the parent resumes execution and exits by means of

1150-428: The community project, while some keep their changes as their own competitive advantages. In proprietary software , the copyright is usually held by the employing entity, not by the individual software developers. Proprietary code is thus more commonly forked when the owner needs to develop two or more versions, such as a windowed version and a command line version, or versions for differing operating systems, such as

1196-433: The designers of Unix, includes fork but also a variant called "rfork" that permits fine-grained sharing of resources between parent and child processes, including the address space (except for a stack segment, which is unique to each process), environment variables and the filesystem namespace; this makes it a unified interface for the creation of both processes and threads within them. Both FreeBSD and IRIX adopted

1242-458: The fork. A notable proprietary fork not of this kind is the many varieties of proprietary Unix —almost all derived from AT&T Unix under license and all called "Unix", but increasingly mutually incompatible. See Unix wars . Fork (system call) In computing , particularly in the context of the Unix operating system and its workalikes , fork is an operation whereby a process creates

1288-534: The implementation by L. Peter Deutsch of fork in the GENIE time-sharing system , where the concept was borrowed by Ken Thompson for its earliest appearance in Research Unix . Fork later became a standard interface in POSIX . The child process starts off with a copy of its parent's file descriptors . For interprocess communication, the parent process will often create one or several pipes , and then after forking

1334-454: The larger group, or whoever controls the web site, will retain the full original name and the associated user community. Thus, there is a reputation penalty associated with forking. The relationship between the different teams can be cordial or very bitter. On the other hand, a friendly fork or a soft fork is a fork that does not intend to compete, but wants to eventually merge with the original. Eric S. Raymond , in his essay Homesteading

1380-522: The onus for calling vfork lies with the programmer. The difference between the System V approach and the BSD approach is philosophical: Should the kernel hide idiosyncrasies of its implementation from users, or should it allow sophisticated users the opportunity to take advantage of the implementation to do a logical function more efficiently? Similarly, the Linux man page for vfork strongly discourages its use: It

1426-473: The original design of the VMS operating system (1977), a copy operation with subsequent mutation of the content of a few specific addresses for the new process as in forking was considered risky. Errors in the current process state may be copied to a child process. Here, the metaphor of process spawning is used: each component of the memory layout of the new process is newly constructed from scratch. The spawn metaphor

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1472-406: The other. The fork operation creates a separate address space for the child. The child process has an exact copy of all the memory segments of the parent process. In modern UNIX variants that follow the virtual memory model from SunOS -4.0, copy-on-write semantics are implemented and the physical memory need not be actually copied. Instead, virtual memory pages in both processes may refer to

1518-413: The parent and memory pages are shared among the parent and child process with no copying done, and in particular with no copy-on-write semantics; hence, if the child process makes a modification in any of the shared pages, no new page will be created and the modified pages are visible to the parent process too. Since there is absolutely no page copying involved (consuming additional memory), this technique

1564-418: The point where fork has returned. To make the processes perform different tasks, the program must branch on the return value of fork to determine whether it is executing as the child process or the parent process. In the child process, the return value appears as zero (which is an invalid process identifier). The child process prints the desired greeting message, then exits. (For technical reasons,

1610-424: The processes will close the ends of the pipes that they do not need. Vfork is a variant of fork with the same calling convention and much the same semantics, but only to be used in restricted situations. It originated in the 3BSD version of Unix, the first Unix to support virtual memory. It was standardized by POSIX, which permitted vfork to have exactly the same behavior as fork, but was marked obsolescent in

1656-652: The rfork system call from Plan 9, the latter renaming it "sproc". clone is a system call in the Linux kernel that creates a child process that may share parts of its execution context with the parent. Like FreeBSD's rfork and IRIX's sproc, Linux's clone was inspired by Plan 9's rfork and can be used to implement threads (though application programmers will typically use a higher-level interface such as pthreads , implemented on top of clone). The "separate stacks" feature from Plan 9 and IRIX has been omitted because (according to Linus Torvalds ) it causes too much overhead. In

1702-439: The same pages of physical memory until one of them writes to such a page: then it is copied. This optimization is important in the common case where fork is used in conjunction with exec to execute a new program: typically, the child process performs only a small set of actions before it ceases execution of its program in favour of the program to be started, and it requires very few, if any, of its parent's data structures . When

1748-476: The successor groups over issues of legitimacy, succession, and design direction. There is serious social pressure against forking. As a result, major forks (such as the Gnu-Emacs / XEmacs split, the fissioning of the 386BSD group into three daughter projects, and the short-lived GCC/EGCS split) are rare enough that they are remembered individually in hacker folklore. David A. Wheeler notes four possible outcomes of

1794-401: The technical, social and financial barriers to forking a source code repository are massively reduced, and GitHub uses "fork" as its term for this method of contribution to a project. Forks often restart version numbering from numbers typically used for initial versions of programs like 0.0.1, 0.1, or 1.0 even if the original software was at another version such as 3.0, 4.0, or 5.0. An exception

1840-399: The user's IP address to third-party search providers. In August 2016, Mozilla , the developer of Firefox, made a minority investment in Cliqz. Cliqz planned to eventually monetize the software through a program known as Cliqz Offers, which would deliver sponsored offers to users based on their interests and browsing history. However, these recommendations would be processed locally based on

1886-553: The user's browsing history and activities. The press release noted that "Users who receive a version of Firefox with Cliqz will have their browsing activity sent to Cliqz servers, including the URLs of pages they visit," and that "Cliqz uses several techniques to attempt to remove sensitive information from this browsing data before it is sent from Firefox." According to the Firefox support website, this version of Firefox collects and sends data to

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1932-463: The whole community a chance to benefit from your changes. Access to the source code is a precondition for this. 3. Derived Works: The license must allow modifications and derived works, and must allow them to be distributed under the same terms as the license of the original software. In free software, forks often result from a schism over different goals or personality clashes. In a fork, both parties assume nearly identical code bases, but typically only

1978-567: Was in use in the present sense by 1995 to describe the XEmacs split, and was an understood usage in the GNU Project by 1996. Free and open-source software may be legally forked without prior approval of those currently developing, managing, or distributing the software per both The Free Software Definition and The Open Source Definition : The freedom to distribute copies of your modified versions to others (freedom 3). By doing this, you can give

2024-414: Was introduced, because the memory sharing that it causes is error-prone: Vfork does not copy page tables so it is faster than the System V fork implementation. But the child process executes in the same physical address space as the parent process (until an exec or exit ) and can thus overwrite the parent's data and stack. A dangerous situation could arise if a programmer uses vfork incorrectly, so

2070-606: Was later adopted in Microsoft operating systems (1993). The POSIX-compatibility component of VM/CMS (OpenExtensions) provides a very limited implementation of fork, in which the parent is suspended while the child executes, and the child and the parent share the same address space. This is essentially a vfork labelled as a fork . (This applies to the CMS guest operating system only; other VM guest operating systems, such as Linux, provide standard fork functionality.) The following variant of

2116-470: Was owned and managed as part of a partnership with Proxy . Lumen was financially profitable, but was discontinued on May 1, 2020 because of changing directors at Cliqz. Fork (software development) In software engineering , a project fork happens when developers take a copy of source code from one software package and start independent development on it, creating a distinct and separate piece of software. The term often implies not merely

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