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Wikipedia

Git

December 02, 2023

For other uses, see Git (disambiguation).
Not to be confused with GitHub, GitLab, or Gitea.

Git (/ɡɪt/)[8] is a distributed version control system[9] that tracks changes in any set of computer files, usually used for coordinating work among programmers who are collaboratively developing source code during software development. Its goals include speed, data integrity, and support for distributed, non-linear workflows (thousands of parallel branches running on different computers).[10][11][12]

Git
A command-line session showing repository creation, addition of a file, and remote synchronization
Original author(s)Linus Torvalds[1]
Developer(s)Junio Hamano and others[2]
Initial release7 April 2005; 18 years ago (2005-04-07)
Stable release
2.43.0[3]  / 20 November 2023
Repository
  • git.kernel.org/pub/scm/git/git.git
Written inPrimarily in C, with GUI and programming scripts written in Shell script, Perl, Tcl and Python[4][5]
Operating systemPOSIX (Linux, macOS, Solaris, AIX), Windows
Available inEnglish
TypeVersion control
LicenseGPL-2.0-only[i][7]
Websitegit-scm.com 

Git was originally authored by Linus Torvalds in 2005 for development of the Linux kernel, with other kernel developers contributing to its initial development.[13] Since 2005, Junio Hamano has been the core maintainer. As with most other distributed version control systems, and unlike most client–server systems, every Git directory on every computer is a full-fledged repository with complete history and full version-tracking abilities, independent of network access or a central server.[14] Git is free and open-source software shared under the GPL-2.0-only license.

Since its creation, Git has become the most popular distributed version control system, with nearly 95% of developers reporting it as their primary version control system as of 2022.[15] There are many popular offerings of Git repository services, including GitHub, SourceForge, Bitbucket and GitLab.[16][17][18][19][20]

History edit

Git development was started by Torvalds in April 2005 when the proprietary source-control management (SCM) system used for Linux kernel development since 2002, BitKeeper, revoked its free license for Linux development.[21][22] The copyright holder of BitKeeper, Larry McVoy, claimed that Andrew Tridgell had created SourcePuller by reverse engineering the BitKeeper protocols.[23] The same incident also spurred the creation of another version-control system, Mercurial.

Torvalds wanted a distributed system that he could use like BitKeeper, but none of the available free systems met his needs. He cited an example of a source-control management system needing 30 seconds to apply a patch and update all associated metadata, and noted that this would not scale to the needs of Linux kernel development, where synchronizing with fellow maintainers could require 250 such actions at once. For his design criterion, he specified that patching should take no more than three seconds, and added three more goals:[10]

  • Take the Concurrent Versions System (CVS) as an example of what not to do; if in doubt, make the exact opposite decision.[12]
  • Support a distributed, BitKeeper-like workflow.[12]
  • Include very strong safeguards against corruption, either accidental or malicious.[11]

These criteria eliminated every version-control system in use at the time, so immediately after the 2.6.12-rc2 Linux kernel development release, Torvalds set out to write his own.[12]

The development of Git began on 3 April 2005.[24] Torvalds announced the project on 6 April and became self-hosting the next day.[24][25] The first merge of multiple branches took place on 18 April.[26] Torvalds achieved his performance goals; on 29 April, the nascent Git was benchmarked recording patches to the Linux kernel tree at a rate of 6.7 patches per second.[27] On 16 June, Git managed the kernel 2.6.12 release.[28]

Torvalds turned over maintenance on 26 July 2005 to Junio Hamano, a major contributor to the project.[29] Hamano was responsible for the 1.0 release on 21 December 2005.[30]

Naming edit

Torvalds sarcastically quipped about the name git (which means "unpleasant person" in British English slang): "I'm an egotistical bastard, and I name all my projects after myself. First 'Linux', now 'git'."[31][32] The man page describes Git as "the stupid content tracker".[33]

The read-me file of the source code elaborates further:[34]

"git" can mean anything, depending on your mood.

  • Random three-letter combination that is pronounceable, and not actually used by any common UNIX command. The fact that it is a mispronunciation of "get" may or may not be relevant.
  • Stupid. Contemptible and despicable. Simple. Take your pick from the dictionary of slang.
  • "Global information tracker": you're in a good mood, and it actually works for you. Angels sing, and a light suddenly fills the room.
  • "Goddamn idiotic truckload of sh*t": when it breaks.

The source code for Git refers to the program as "the information manager from hell".

Releases edit

List of Git releases:[35]

Version Original release date Latest (patch) version Patch release date Notable changes
Old version, no longer maintained: 0.99 2005-07-11 0.99.9n 2005-12-15
Old version, no longer maintained: 1.0 2005-12-21 1.0.13 2006-01-27
Old version, no longer maintained: 1.1 2006-01-08 1.1.6 2006-01-30
Old version, no longer maintained: 1.2 2006-02-12 1.2.6 2006-04-08
Old version, no longer maintained: 1.3 2006-04-18 1.3.3 2006-05-16
Old version, no longer maintained: 1.4 2006-06-10 1.4.4.5 2008-07-16
Old version, no longer maintained: 1.5 2007-02-14 1.5.6.6 2008-12-17
Old version, no longer maintained: 1.6 2008-08-17 1.6.6.3 2010-12-15
Old version, no longer maintained: 1.7 2010-02-13 1.7.12.4 2012-10-17
Old version, no longer maintained: 1.8 2012-10-21 1.8.5.6 2014-12-17
Old version, no longer maintained: 1.9 2014-02-14 1.9.5 2014-12-17
Old version, no longer maintained: 2.0 2014-05-28 2.0.5 2014-12-17
Old version, no longer maintained: 2.1 2014-08-16 2.1.4 2014-12-17
Old version, no longer maintained: 2.2 2014-11-26 2.2.3 2015-09-04
Old version, no longer maintained: 2.3 2015-02-05 2.3.10 2015-09-29
Old version, no longer maintained: 2.4 2015-04-30 2.4.12 2017-05-05
Old version, no longer maintained: 2.5 2015-07-27 2.5.6 2017-05-05
Old version, no longer maintained: 2.6 2015-09-28 2.6.7 2017-05-05
Old version, no longer maintained: 2.7 2015-10-04 2.7.6 2017-07-30
Old version, no longer maintained: 2.8 2016-03-28 2.8.6 2017-07-30
Old version, no longer maintained: 2.9 2016-06-13 2.9.5 2017-07-30
Old version, no longer maintained: 2.10 2016-09-02 2.10.5 2017-09-22
Old version, no longer maintained: 2.11 2016-11-29 2.11.4 2017-09-22
Old version, no longer maintained: 2.12 2017-02-24 2.12.5 2017-09-22
Old version, no longer maintained: 2.13 2017-05-10 2.13.7 2018-05-22
Old version, no longer maintained: 2.14 2017-08-04 2.14.6 2019-12-07
Old version, no longer maintained: 2.15 2017-10-30 2.15.4 2019-12-07
Old version, no longer maintained: 2.16 2018-01-17 2.16.6 2019-12-07
Old version, no longer maintained: 2.17 2018-04-02 2.17.6 2021-03-09
Old version, no longer maintained: 2.18 2018-06-21 2.18.5 2021-03-09
Old version, no longer maintained: 2.19 2018-09-10 2.19.6 2021-03-09
Old version, no longer maintained: 2.20 2018-12-09 2.20.5 2021-03-09
Old version, no longer maintained: 2.21 2019-02-24 2.21.4 2021-03-09
Old version, no longer maintained: 2.22 2019-06-07 2.22.5 2021-03-09
Old version, no longer maintained: 2.23 2019-08-16 2.23.4 2021-03-09
  • Introducing git restore and git switch

[36]

Old version, no longer maintained: 2.24 2019-11-04 2.24.4 2021-03-09
Old version, no longer maintained: 2.25 2020-01-13 2.25.5 2021-03-09 Sparse checkout management made easy[37]
Old version, no longer maintained: 2.26 2020-03-22 2.26.3 2021-03-09
  • Protocol version 2 is now the default
  • Some new config tricks
  • Updates to git sparse-checkout

[38]

Old version, no longer maintained: 2.27 2020-06-01 2.27.1 2021-03-09
Old version, no longer maintained: 2.28 2020-07-27 2.28.1 2021-03-09
  • Introducing init.defaultBranch
  • Changed-path Bloom filter

[39]

Old version, no longer maintained: 2.29 2020-10-19 2.29.3 2021-03-09
  • Experimental SHA-256 support
  • Negative refspecs
  • New git shortlog tricks

[40]

Older version, yet still maintained: 2.30 2020-12-27 2.30.9 2023-04-25
  • Userdiff for PHP update, Rust, CSS update
  • The command line completion script (in contrib/) learned that "git stash show" takes the options "git diff" takes.

[41]

Older version, yet still maintained: 2.31 2021-03-15 2.31.8 2023-04-25
  • git difftool adds --skip-to option
  • --format enhancements for machine readable
  • git pull warning to specify rebase or merge

[42][43]

Older version, yet still maintained: 2.32 2021-06-06 2.32.7 2023-04-25
Older version, yet still maintained: 2.33 2021-08-16 2.33.8 2023-04-25
Older version, yet still maintained: 2.34 2021-11-15 2.34.8 2023-04-25
Older version, yet still maintained: 2.35 2022-01-25 2.35.8 2023-04-25
Older version, yet still maintained: 2.36 2022-04-18 2.36.6 2023-04-25
Older version, yet still maintained: 2.37 2022-06-27 2.37.7 2023-04-25
Older version, yet still maintained: 2.38 2022-10-02 2.38.5 2023-04-25
Older version, yet still maintained: 2.39 2022-12-12 2.39.3 2023-04-25
Older version, yet still maintained: 2.40 2023-03-14 2.40.1 2023-04-25
Older version, yet still maintained: 2.41 2023-06-01 2.41.0
Current stable version: 2.42 2023-08-21 2.42.0
Legend:
Old version
Older version, still maintained
Latest version
Latest preview version
Future release
Sources:[44][45]

Design

Git's design was inspired by BitKeeper and Monotone.[46][47] Git was originally designed as a low-level version-control system engine, on top of which others could write front ends, such as Cogito or StGIT.[47] The core Git project has since become a complete version-control system that is usable directly.[48] While strongly influenced by BitKeeper, Torvalds deliberately avoided conventional approaches, leading to a unique design.[49]

Characteristics edit

Git's design is a synthesis of Torvalds's experience with Linux in maintaining a large distributed development project, along with his intimate knowledge of file-system performance gained from the same project and the urgent need to produce a working system in short order. These influences led to the following implementation choices:[13]

Strong support for non-linear development
Git supports rapid branching and merging, and includes specific tools for visualizing and navigating a non-linear development history. In Git, a core assumption is that a change will be merged more often than it is written, as it is passed around to various reviewers. In Git, branches are very lightweight: a branch is only a reference to one commit.
Distributed development
Like Darcs, BitKeeper, Mercurial, Bazaar, and Monotone, Git gives each developer a local copy of the full development history, and changes are copied from one such repository to another. These changes are imported as added development branches and can be merged in the same way as a locally developed branch.[50]
Compatibility with existing systems and protocols
Repositories can be published via Hypertext Transfer Protocol Secure (HTTPS), Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP), or a Git protocol over either a plain socket or Secure Shell (ssh). Git also has a CVS server emulation, which enables the use of existing CVS clients and IDE plugins to access Git repositories. Subversion repositories can be used directly with git-svn.[51]
Efficient handling of large projects
Torvalds has described Git as being very fast and scalable,[52] and performance tests done by Mozilla[53] showed that it was an order of magnitude faster diffing large repositories than Mercurial and GNU Bazaar; fetching version history from a locally stored repository can be one hundred times faster than fetching it from the remote server.[54]
Cryptographic authentication of history
The Git history is stored in such a way that the ID of a particular version (a commit in Git terms) depends upon the complete development history leading up to that commit. Once it is published, it is not possible to change the old versions without it being noticed. The structure is similar to a Merkle tree, but with added data at the nodes and leaves.[55] (Mercurial and Monotone also have this property.)
Toolkit-based design
Git was designed as a set of programs written in C and several shell scripts that provide wrappers around those programs.[56] Although most of those scripts have since been rewritten in C for speed and portability, the design remains, and it is easy to chain the components together.[57]
Pluggable merge strategies
As part of its toolkit design, Git has a well-defined model of an incomplete merge, and it has multiple algorithms for completing it, culminating in telling the user that it is unable to complete the merge automatically and that manual editing is needed.[58]
Garbage accumulates until collected
Aborting operations or backing out changes will leave useless dangling objects in the database. These are generally a small fraction of the continuously growing history of wanted objects. Git will automatically perform garbage collection when enough loose objects have been created in the repository. Garbage collection can be called explicitly using git gc.[59][60]
Periodic explicit object packing
Git stores each newly created object as a separate file. Although individually compressed, this takes up a great deal of space and is inefficient. This is solved by the use of packs that store a large number of objects delta-compressed among themselves in one file (or network byte stream) called a packfile. Packs are compressed using the heuristic that files with the same name are probably similar, without depending on this for correctness. A corresponding index file is created for each packfile, telling the offset of each object in the packfile. Newly created objects (with newly added history) are still stored as single objects, and periodic repacking is needed to maintain space efficiency. The process of packing the repository can be very computationally costly. By allowing objects to exist in the repository in a loose but quickly generated format, Git allows the costly pack operation to be deferred until later, when time matters less, e.g., the end of a workday. Git does periodic repacking automatically, but manual repacking is also possible with the git gc command.[61] For data integrity, both the packfile and its index have an SHA-1 checksum[62] inside, and the file name of the packfile also contains an SHA-1 checksum. To check the integrity of a repository, run the git fsck command.[63][64]

Another property of Git is that it snapshots directory trees of files. The earliest systems for tracking versions of source code, Source Code Control System (SCCS) and Revision Control System (RCS), worked on individual files and emphasized the space savings to be gained from interleaved deltas (SCCS) or delta encoding (RCS) the (mostly similar) versions. Later revision-control systems maintained this notion of a file having an identity across multiple revisions of a project. However, Torvalds rejected this concept.[65] Consequently, Git does not explicitly record file revision relationships at any level below the source-code tree.

These implicit revision relationships have some significant consequences:

  • It is slightly more costly to examine the change history of one file than the whole project.[66] To obtain a history of changes affecting a given file, Git must walk the global history and then determine whether each change modified that file. This method of examining history does, however, let Git produce with equal efficiency a single history showing the changes to an arbitrary set of files. For example, a subdirectory of the source tree plus an associated global header file is a very common case.
  • Renames are handled implicitly rather than explicitly. A common complaint with CVS is that it uses the name of a file to identify its revision history, so moving or renaming a file is not possible without either interrupting its history or renaming the history and thereby making the history inaccurate. Most post-CVS revision-control systems solve this by giving a file a unique long-lived name (analogous to an inode number) that survives renaming. Git does not record such an identifier, and this is claimed as an advantage.[67][68] Source code files are sometimes split or merged, or simply renamed,[69] and recording this as a simple rename would freeze an inaccurate description of what happened in the (immutable) history. Git addresses the issue by detecting renames while browsing the history of snapshots rather than recording it when making the snapshot.[70] (Briefly, given a file in revision N, a file of the same name in revision N − 1 is its default ancestor. However, when there is no like-named file in revision N − 1, Git searches for a file that existed only in revision N − 1 and is very similar to the new file.) However, it does require more CPU-intensive work every time the history is reviewed, and several options to adjust the heuristics are available. This mechanism does not always work; sometimes a file that is renamed with changes in the same commit is read as a deletion of the old file and the creation of a new file. Developers can work around this limitation by committing the rename and the changes separately.

Git implements several merging strategies; a non-default strategy can be selected at merge time:[71]

  • resolve: the traditional three-way merge algorithm.
  • recursive: This is the default when pulling or merging one branch, and is a variant of the three-way merge algorithm.

    When there are more than one common ancestors that can be used for a three-way merge, it creates a merged tree of the common ancestors and uses that as the reference tree for the three-way merge. This has been reported to result in fewer merge conflicts without causing mis-merges by tests done on prior merge commits taken from Linux 2.6 kernel development history. Also, this can detect and handle merges involving renames.

    — Linus Torvalds[72]
  • octopus: This is the default when merging more than two heads.

Data structures edit

Git's primitives are not inherently a source-code management system. Torvalds explains:[73]

In many ways you can just see git as a filesystem—it's content-addressable, and it has a notion of versioning, but I really designed it coming at the problem from the viewpoint of a filesystem person (hey, kernels is what I do), and I actually have absolutely zero interest in creating a traditional SCM system.

From this initial design approach, Git has developed the full set of features expected of a traditional SCM,[48] with features mostly being created as needed, then refined and extended over time.

 
Some data flows and storage levels in the Git revision control system

Git has two data structures: a mutable index (also called stage or cache) that caches information about the working directory and the next revision to be committed; and an immutable, append-only object database.

The index serves as a connection point between the object database and the working tree.

The object store contains five types of objects:[74][63]

  • A blob is the content of a file. Blobs have no proper file name, time stamps, or other metadata (a blob's name internally is a hash of its content[75]). In git, each blob is a version of a file, in which is the file's data.[76]
  • A tree object is the equivalent of a directory. It contains a list of file names,[77] each with some type bits and a reference to a blob or tree object that is that file, symbolic link, or directory's contents. These objects are a snapshot of the source tree. (In whole, this comprises a Merkle tree, meaning that only a single hash for the root tree is sufficient and actually used in commits to precisely pinpoint to the exact state of whole tree structures of any number of sub-directories and files.)
  • A commit object links tree objects together into history. It contains the name of a tree object (of the top-level source directory), a timestamp, a log message, and the names of zero or more parent commit objects.[78]
  • A tag object is a container that contains a reference to another object and can hold added meta-data related to another object. Most commonly, it is used to store a digital signature of a commit object corresponding to a particular release of the data being tracked by Git.[79]
  • A packfile object collects various other objects into a zlib-compressed bundle for compactness and ease of transport over network protocols.[80]

Each object is identified by a SHA-1 hash of its contents. Git computes the hash and uses this value for the object's name. The object is put into a directory matching the first two characters of its hash. The rest of the hash is used as the file name for that object.

Git stores each revision of a file as a unique blob. The relationships between the blobs can be found through examining the tree and commit objects. Newly added objects are stored in their entirety using zlib compression. This can consume a large amount of disk space quickly, so objects can be combined into packs, which use delta compression to save space, storing blobs as their changes relative to other blobs.

Additionally, git stores labels called refs (short for references) to indicate the locations of various commits. They are stored in the reference database and are respectively:[81]

  • Heads (branches): Named references that are advanced automatically to the new commit when a commit is made on top of them.
  • HEAD: A reserved head that will be compared against the working tree to create a commit.
  • Tags: Like branch references but fixed to a particular commit. Used to label important points in history.

References edit

Every object in the Git database that is not referred to may be cleaned up by using a garbage collection command or automatically. An object may be referenced by another object or an explicit reference. Git knows different types of references. The commands to create, move, and delete references vary. git show-ref lists all references. Some types are:

  • heads: refers to an object locally,
  • remotes: refers to an object which exists in a remote repository,
  • stash: refers to an object not yet committed,
  • meta: e.g. a configuration in a bare repository, user rights; the refs/meta/config namespace was introduced retrospectively, gets used by Gerrit,[82]
  • tags: see above.

Implementations edit

 
gitg is a graphical front-end using GTK+.

Git (the main implementation in C) is primarily developed on Linux, although it also supports most major operating systems, including the BSDs (DragonFly BSD, FreeBSD, NetBSD, and OpenBSD), Solaris, macOS, and Windows.[83][84]

The first Windows port of Git was primarily a Linux-emulation framework that hosts the Linux version. Installing Git under Windows creates a similarly named Program Files directory containing the Mingw-w64 port of the GNU Compiler Collection, Perl 5, MSYS2 (itself a fork of Cygwin, a Unix-like emulation environment for Windows) and various other Windows ports or emulations of Linux utilities and libraries. Currently, native Windows builds of Git are distributed as 32- and 64-bit installers.[85] The git official website currently maintains a build of Git for Windows, still using the MSYS2 environment.[86]

The JGit implementation of Git is a pure Java software library, designed to be embedded in any Java application. JGit is used in the Gerrit code-review tool, and in EGit, a Git client for the Eclipse IDE.[87]

Go-git is an open-source implementation of Git written in pure Go.[88] It is currently used for backing projects as a SQL interface for Git code repositories[89] and providing encryption for Git.[90]

The Dulwich implementation of Git is a pure Python software component for Python 2.7, 3.4 and 3.5.[91]

The libgit2 implementation of Git is an ANSI C software library with no other dependencies, which can be built on multiple platforms, including Windows, Linux, macOS, and BSD.[92] It has bindings for many programming languages, including Ruby, Python, and Haskell.[93][94][95]

JS-Git is a JavaScript implementation of a subset of Git.[96]

Git server edit

 
Screenshot of Gitweb interface showing a commit diff

As Git is a distributed version control system, it could be used as a server out of the box. It is shipped with a built-in command git daemon which starts a simple TCP server running on the Git protocol.[97][98] Dedicated Git HTTP servers help (amongst other features) by adding access control, displaying the contents of a Git repository via the web interfaces, and managing multiple repositories. Already existing Git repositories can be cloned and shared to be used by others as a centralized repo. It can also be accessed via remote shell just by having the Git software installed and allowing a user to log in.[99] Git servers typically listen on TCP port 9418.[100]

Open source edit

  • Hosting the Git server using the Git Binary.[101]
  • Gerrit, a Git server configurable to support code reviews and provide access via ssh, an integrated Apache MINA or OpenSSH, or an integrated Jetty web server. Gerrit provides integration for LDAP, Active Directory, OpenID, OAuth, Kerberos/GSSAPI, X509 https client certificates. With Gerrit 3.0 all configurations will be stored as Git repositories, and no database is required to run. Gerrit has a pull-request feature implemented in its core but lacks a GUI for it.
  • Phabricator, a spin-off from Facebook. As Facebook primarily uses Mercurial, Git support is not as prominent.[102]
  • RhodeCode Community Edition (CE), supporting Git, Mercurial and Subversion with an AGPLv3 license.
  • Kallithea, supporting both Git and Mercurial, developed in Python with GPL license.
  • External projects like gitolite,[103] which provide scripts on top of Git software to provide fine-grained access control.
  • There are several other FLOSS solutions for self-hosting, including Gogs[104] and Gitea, a fork of Gogs, both developed in Go language with MIT license.

Git server as a service edit

See also: Comparison of source-code-hosting facilities

There are many offerings of Git repositories as a service. The most popular are GitHub, SourceForge, Bitbucket and GitLab.[38][17][18][19][20]

Adoption edit

The Eclipse Foundation reported in its annual community survey that as of May 2014, Git is now the most widely used source-code management tool, with 42.9% of professional software developers reporting that they use Git as their primary source-control system[105] compared with 36.3% in 2013, 32% in 2012; or for Git responses excluding use of GitHub: 33.3% in 2014, 30.3% in 2013, 27.6% in 2012 and 12.8% in 2011.[106] Open-source directory Black Duck Open Hub reports a similar uptake among open-source projects.[107]

Stack Overflow has included version control in their annual developer survey[108] in 2015 (16,694 responses),[109] 2017 (30,730 responses),[110] 2018 (74,298 responses)[111] and 2022 (71,379 responses).[15] Git was the overwhelming favorite of responding developers in these surveys, reporting as high as 93.9% in 2022.

Version control systems used by responding developers:

Name 2015 2017 2018 2022
Git 69.3% 69.2% 87.2% 93.9%
Subversion 36.9% 9.1% 16.1% 5.2%
TFVC 12.2% 7.3% 10.9% [ii]
Mercurial 7.9% 1.9% 3.6% 1.1%
CVS 4.2% [ii] [ii] [ii]
Perforce 3.3% [ii] [ii] [ii]
VSS [ii] 0.6% [ii] [ii]
ClearCase [ii] 0.4% [ii] [ii]
Zip file backups [ii] 2.0% 7.9% [ii]
Raw network sharing [ii] 1.7% 7.9% [ii]
Other 5.8% 3.0% [ii] [ii]
None 9.3% 4.8% 4.8% 4.3%

The UK IT jobs website itjobswatch.co.uk reports that as of late September 2016, 29.27% of UK permanent software development job openings have cited Git,[112] ahead of 12.17% for Microsoft Team Foundation Server,[113] 10.60% for Subversion,[114] 1.30% for Mercurial,[115] and 0.48% for Visual SourceSafe.[116]

Extensions edit

There are many Git extensions, like Git LFS, which started as an extension to Git in the GitHub community and is now widely used by other repositories. Extensions are usually independently developed and maintained by different people, but at some point in the future, a widely used extension can be merged with Git.

Other open-source Git extensions include:

  • git-annex, a distributed file synchronization system based on Git
  • git-flow, a set of Git extensions to provide high-level repository operations for Vincent Driessen's branching model
  • git-machete, a repository organizer & tool for automating rebase/merge/pull/push operations

Microsoft developed the Virtual File System for Git (VFS for Git; formerly Git Virtual File System or GVFS) extension to handle the size of the Windows source-code tree as part of their 2017 migration from Perforce. VFS for Git allows cloned repositories to use placeholders whose contents are downloaded only once a file is accessed.[117]

Conventions edit

Git does not impose many restrictions on how it should be used, but some conventions are adopted in order to organize histories, especially those which require the cooperation of many contributors.

  • The master branch is created by default with git init [76][118] and is often used as the branch that other changes are merged into.[119] Correspondingly, the default name of the upstream remote is origin[120] and so the name of the default remote branch is origin/master. The use of master as the default branch name is not universally true; repositories created in GitHub and GitLab initialize with a main branch instead of master,[121][122] though the default can be changed by the user.
  • Pushed commits should usually not be overwritten, but should rather be reverted[123] (a commit is made on top which reverses the changes to an earlier commit). This prevents shared new commits based on shared commits from being invalid because the commit on which they are based does not exist in the remote. If the commits contain sensitive information, they should be removed, which involves a more complex procedure to rewrite history.
  • The git-flow[124] workflow and naming conventions are often adopted to distinguish feature specific unstable histories (feature/*), unstable shared histories (develop), production ready histories (main), and emergency patches to released products (hotfix).
  • Pull requests are not a feature of git, but are commonly provided by git cloud services. A pull request is a request by one user to merge a branch of their repository fork into another repository sharing the same history (called the upstream remote).[125][126] The underlying function of a pull request is no different than that of an administrator of a repository pulling changes from another remote (the repository that is the source of the pull request). However, the pull request itself is a ticket managed by the hosting server which initiates scripts to perform these actions; it is not a feature of git SCM.

Security edit

Git does not provide access-control mechanisms, but was designed for operation with other tools that specialize in access control.[127]

On 17 December 2014, an exploit was found affecting the Windows and macOS versions of the Git client. An attacker could perform arbitrary code execution on a target computer with Git installed by creating a malicious Git tree (directory) named .git (a directory in Git repositories that stores all the data of the repository) in a different case (such as .GIT or .Git, needed because Git does not allow the all-lowercase version of .git to be created manually) with malicious files in the .git/hooks subdirectory (a folder with executable files that Git runs) on a repository that the attacker made or on a repository that the attacker can modify. If a Windows or Mac user pulls (downloads) a version of the repository with the malicious directory, then switches to that directory, the .git directory will be overwritten (due to the case-insensitive trait of the Windows and Mac filesystems) and the malicious executable files in .git/hooks may be run, which results in the attacker's commands being executed. An attacker could also modify the .git/config configuration file, which allows the attacker to create malicious Git aliases (aliases for Git commands or external commands) or modify extant aliases to execute malicious commands when run. The vulnerability was patched in version 2.2.1 of Git, released on 17 December 2014, and announced the next day.[128][129]

Git version 2.6.1, released on 29 September 2015, contained a patch for a security vulnerability (CVE-2015-7545)[130] that allowed arbitrary code execution.[131] The vulnerability was exploitable if an attacker could convince a victim to clone a specific URL, as the arbitrary commands were embedded in the URL itself.[132] An attacker could use the exploit via a man-in-the-middle attack if the connection was unencrypted,[132] as they could redirect the user to a URL of their choice. Recursive clones were also vulnerable since they allowed the controller of a repository to specify arbitrary URLs via the gitmodules file.[132]

Git uses SHA-1 hashes internally. Linus Torvalds has responded that the hash was mostly to guard against accidental corruption, and the security a cryptographically secure hash gives was just an accidental side effect, with the main security being signing elsewhere.[133][134] Since a demonstration of the SHAttered attack against git in 2017, git was modified to use a SHA-1 variant resistant to this attack. A plan for hash function transition is being written since February 2020.[135]

Trademark edit

"Git" is a registered word trademark of Software Freedom Conservancy under US500000085961336 since 2015-02-03.

See also edit

Notes edit

  1. ^ GPL-2.0-only since 2005-04-11. Some parts under compatible licenses such as LGPLv2.1.[6]
  2. ^ a b c d e f g h i j k l m n o p q r s Not listed as an option in this survey

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References edit

  • Chacon, Scott (24 December 2014). Pro Git (2nd ed.). New York, NY: Apress. ISBN 978-1-4842-0077-3. from the original on 25 December 2015.

External links edit

 
Wikimedia Commons has media related to Git.
 
Wikibooks has a book on the topic of: Git

December 02, 2023
other, uses, disambiguation, confused, with, this, article, lead, section, short, adequately, summarize, points, please, consider, expanding, lead, provide, accessible, overview, important, aspects, article, april, 2023, distributed, version, control, system, . For other uses see Git disambiguation Not to be confused with GitHub GitLab or Gitea This article s lead section may be too short to adequately summarize the key points Please consider expanding the lead to provide an accessible overview of all important aspects of the article April 2023 Git ɡ ɪ t 8 is a distributed version control system 9 that tracks changes in any set of computer files usually used for coordinating work among programmers who are collaboratively developing source code during software development Its goals include speed data integrity and support for distributed non linear workflows thousands of parallel branches running on different computers 10 11 12 GitA command line session showing repository creation addition of a file and remote synchronizationOriginal author s Linus Torvalds 1 Developer s Junio Hamano and others 2 Initial release7 April 2005 18 years ago 2005 04 07 Stable release2 43 0 3 20 November 2023Repositorygit wbr kernel wbr org wbr pub wbr scm wbr git wbr git wbr gitWritten inPrimarily in C with GUI and programming scripts written in Shell script Perl Tcl and Python 4 5 Operating systemPOSIX Linux macOS Solaris AIX WindowsAvailable inEnglishTypeVersion controlLicenseGPL 2 0 only i 7 Websitegit scm wbr com Git was originally authored by Linus Torvalds in 2005 for development of the Linux kernel with other kernel developers contributing to its initial development 13 Since 2005 Junio Hamano has been the core maintainer As with most other distributed version control systems and unlike most client server systems every Git directory on every computer is a full fledged repository with complete history and full version tracking abilities independent of network access or a central server 14 Git is free and open source software shared under the GPL 2 0 only license Since its creation Git has become the most popular distributed version control system with nearly 95 of developers reporting it as their primary version control system as of 2022 15 There are many popular offerings of Git repository services including GitHub SourceForge Bitbucket and GitLab 16 17 18 19 20 Contents 1 History 1 1 Naming 1 2 Releases 2 Design 2 1 Characteristics 2 2 Data structures 2 3 References 3 Implementations 4 Git server 4 1 Open source 4 2 Git server as a service 5 Adoption 5 1 Extensions 6 Conventions 7 Security 8 Trademark 9 See also 10 Notes 11 Citations 12 References 13 External linksHistory editGit development was started by Torvalds in April 2005 when the proprietary source control management SCM system used for Linux kernel development since 2002 BitKeeper revoked its free license for Linux development 21 22 The copyright holder of BitKeeper Larry McVoy claimed that Andrew Tridgell had created SourcePuller by reverse engineering the BitKeeper protocols 23 The same incident also spurred the creation of another version control system Mercurial Torvalds wanted a distributed system that he could use like BitKeeper but none of the available free systems met his needs He cited an example of a source control management system needing 30 seconds to apply a patch and update all associated metadata and noted that this would not scale to the needs of Linux kernel development where synchronizing with fellow maintainers could require 250 such actions at once For his design criterion he specified that patching should take no more than three seconds and added three more goals 10 Take the Concurrent Versions System CVS as an example of what not to do if in doubt make the exact opposite decision 12 Support a distributed BitKeeper like workflow 12 Include very strong safeguards against corruption either accidental or malicious 11 These criteria eliminated every version control system in use at the time so immediately after the 2 6 12 rc2 Linux kernel development release Torvalds set out to write his own 12 The development of Git began on 3 April 2005 24 Torvalds announced the project on 6 April and became self hosting the next day 24 25 The first merge of multiple branches took place on 18 April 26 Torvalds achieved his performance goals on 29 April the nascent Git was benchmarked recording patches to the Linux kernel tree at a rate of 6 7 patches per second 27 On 16 June Git managed the kernel 2 6 12 release 28 Torvalds turned over maintenance on 26 July 2005 to Junio Hamano a major contributor to the project 29 Hamano was responsible for the 1 0 release on 21 December 2005 30 Naming edit Torvalds sarcastically quipped about the name git which means unpleasant person in British English slang I m an egotistical bastard and I name all my projects after myself First Linux now git 31 32 The man page describes Git as the stupid content tracker 33 The read me file of the source code elaborates further 34 git can mean anything depending on your mood Random three letter combination that is pronounceable and not actually used by any common UNIX command The fact that it is a mispronunciation of get may or may not be relevant Stupid Contemptible and despicable Simple Take your pick from the dictionary of slang Global information tracker you re in a good mood and it actually works for you Angels sing and a light suddenly fills the room Goddamn idiotic truckload of sh t when it breaks The source code for Git refers to the program as the information manager from hell Releases edit This section may require cleanup to meet Wikipedia s quality standards The specific problem is Overly detailed changelog Please help improve this section if you can November 2023 Learn how and when to remove this template message List of Git releases 35 Version Original release date Latest patch version Patch release date Notable changesOld version no longer maintained 0 99 2005 07 11 0 99 9n 2005 12 15Old version no longer maintained 1 0 2005 12 21 1 0 13 2006 01 27Old version no longer maintained 1 1 2006 01 08 1 1 6 2006 01 30Old version no longer maintained 1 2 2006 02 12 1 2 6 2006 04 08Old version no longer maintained 1 3 2006 04 18 1 3 3 2006 05 16Old version no longer maintained 1 4 2006 06 10 1 4 4 5 2008 07 16Old version no longer maintained 1 5 2007 02 14 1 5 6 6 2008 12 17Old version no longer maintained 1 6 2008 08 17 1 6 6 3 2010 12 15Old version no longer maintained 1 7 2010 02 13 1 7 12 4 2012 10 17Old version no longer maintained 1 8 2012 10 21 1 8 5 6 2014 12 17Old version no longer maintained 1 9 2014 02 14 1 9 5 2014 12 17Old version no longer maintained 2 0 2014 05 28 2 0 5 2014 12 17Old version no longer maintained 2 1 2014 08 16 2 1 4 2014 12 17Old version no longer maintained 2 2 2014 11 26 2 2 3 2015 09 04Old version no longer maintained 2 3 2015 02 05 2 3 10 2015 09 29Old version no longer maintained 2 4 2015 04 30 2 4 12 2017 05 05Old version no longer maintained 2 5 2015 07 27 2 5 6 2017 05 05Old version no longer maintained 2 6 2015 09 28 2 6 7 2017 05 05Old version no longer maintained 2 7 2015 10 04 2 7 6 2017 07 30Old version no longer maintained 2 8 2016 03 28 2 8 6 2017 07 30Old version no longer maintained 2 9 2016 06 13 2 9 5 2017 07 30Old version no longer maintained 2 10 2016 09 02 2 10 5 2017 09 22Old version no longer maintained 2 11 2016 11 29 2 11 4 2017 09 22Old version no longer maintained 2 12 2017 02 24 2 12 5 2017 09 22Old version no longer maintained 2 13 2017 05 10 2 13 7 2018 05 22Old version no longer maintained 2 14 2017 08 04 2 14 6 2019 12 07Old version no longer maintained 2 15 2017 10 30 2 15 4 2019 12 07Old version no longer maintained 2 16 2018 01 17 2 16 6 2019 12 07Old version no longer maintained 2 17 2018 04 02 2 17 6 2021 03 09Old version no longer maintained 2 18 2018 06 21 2 18 5 2021 03 09Old version no longer maintained 2 19 2018 09 10 2 19 6 2021 03 09Old version no longer maintained 2 20 2018 12 09 2 20 5 2021 03 09Old version no longer maintained 2 21 2019 02 24 2 21 4 2021 03 09Old version no longer maintained 2 22 2019 06 07 2 22 5 2021 03 09Old version no longer maintained 2 23 2019 08 16 2 23 4 2021 03 09 Introducing git restore and git switch 36 Old version no longer maintained 2 24 2019 11 04 2 24 4 2021 03 09Old version no longer maintained 2 25 2020 01 13 2 25 5 2021 03 09 Sparse checkout management made easy 37 Old version no longer maintained 2 26 2020 03 22 2 26 3 2021 03 09 Protocol version 2 is now the default Some new config tricks Updates to git sparse checkout 38 Old version no longer maintained 2 27 2020 06 01 2 27 1 2021 03 09Old version no longer maintained 2 28 2020 07 27 2 28 1 2021 03 09 Introducing init defaultBranch Changed path Bloom filter 39 Old version no longer maintained 2 29 2020 10 19 2 29 3 2021 03 09 Experimental SHA 256 support Negative refspecs New git shortlog tricks 40 Older version yet still maintained 2 30 2020 12 27 2 30 9 2023 04 25 Userdiff for PHP update Rust CSS update The command line completion script in contrib learned that git stash show takes the options git diff takes 41 Older version yet still maintained 2 31 2021 03 15 2 31 8 2023 04 25 git difftool adds skip to option format enhancements for machine readable git pull warning to specify rebase or merge 42 43 Older version yet still maintained 2 32 2021 06 06 2 32 7 2023 04 25Older version yet still maintained 2 33 2021 08 16 2 33 8 2023 04 25Older version yet still maintained 2 34 2021 11 15 2 34 8 2023 04 25Older version yet still maintained 2 35 2022 01 25 2 35 8 2023 04 25Older version yet still maintained 2 36 2022 04 18 2 36 6 2023 04 25Older version yet still maintained 2 37 2022 06 27 2 37 7 2023 04 25Older version yet still maintained 2 38 2022 10 02 2 38 5 2023 04 25Older version yet still maintained 2 39 2022 12 12 2 39 3 2023 04 25Older version yet still maintained 2 40 2023 03 14 2 40 1 2023 04 25Older version yet still maintained 2 41 2023 06 01 2 41 0Current stable version 2 42 2023 08 21 2 42 0Legend Old versionOlder version still maintainedLatest versionLatest preview versionFuture releaseSources 44 45 DesignGit s design was inspired by BitKeeper and Monotone 46 47 Git was originally designed as a low level version control system engine on top of which others could write front ends such as Cogito or StGIT 47 The core Git project has since become a complete version control system that is usable directly 48 While strongly influenced by BitKeeper Torvalds deliberately avoided conventional approaches leading to a unique design 49 Characteristics edit This section needs additional citations for verification Please help improve this article by adding citations to reliable sources in this section Unsourced material may be challenged and removed Find sources Git news newspapers books scholar JSTOR June 2020 Learn how and when to remove this template message Git s design is a synthesis of Torvalds s experience with Linux in maintaining a large distributed development project along with his intimate knowledge of file system performance gained from the same project and the urgent need to produce a working system in short order These influences led to the following implementation choices 13 Strong support for non linear development Git supports rapid branching and merging and includes specific tools for visualizing and navigating a non linear development history In Git a core assumption is that a change will be merged more often than it is written as it is passed around to various reviewers In Git branches are very lightweight a branch is only a reference to one commit Distributed development Like Darcs BitKeeper Mercurial Bazaar and Monotone Git gives each developer a local copy of the full development history and changes are copied from one such repository to another These changes are imported as added development branches and can be merged in the same way as a locally developed branch 50 Compatibility with existing systems and protocols Repositories can be published via Hypertext Transfer Protocol Secure HTTPS Hypertext Transfer Protocol HTTP File Transfer Protocol FTP or a Git protocol over either a plain socket or Secure Shell ssh Git also has a CVS server emulation which enables the use of existing CVS clients and IDE plugins to access Git repositories Subversion repositories can be used directly with git svn 51 Efficient handling of large projects Torvalds has described Git as being very fast and scalable 52 and performance tests done by Mozilla 53 showed that it was an order of magnitude faster diffing large repositories than Mercurial and GNU Bazaar fetching version history from a locally stored repository can be one hundred times faster than fetching it from the remote server 54 Cryptographic authentication of history The Git history is stored in such a way that the ID of a particular version a commit in Git terms depends upon the complete development history leading up to that commit Once it is published it is not possible to change the old versions without it being noticed The structure is similar to a Merkle tree but with added data at the nodes and leaves 55 Mercurial and Monotone also have this property Toolkit based design Git was designed as a set of programs written in C and several shell scripts that provide wrappers around those programs 56 Although most of those scripts have since been rewritten in C for speed and portability the design remains and it is easy to chain the components together 57 Pluggable merge strategies As part of its toolkit design Git has a well defined model of an incomplete merge and it has multiple algorithms for completing it culminating in telling the user that it is unable to complete the merge automatically and that manual editing is needed 58 Garbage accumulates until collected Aborting operations or backing out changes will leave useless dangling objects in the database These are generally a small fraction of the continuously growing history of wanted objects Git will automatically perform garbage collection when enough loose objects have been created in the repository Garbage collection can be called explicitly using git gc 59 60 Periodic explicit object packing Git stores each newly created object as a separate file Although individually compressed this takes up a great deal of space and is inefficient This is solved by the use of packs that store a large number of objects delta compressed among themselves in one file or network byte stream called a packfile Packs are compressed using the heuristic that files with the same name are probably similar without depending on this for correctness A corresponding index file is created for each packfile telling the offset of each object in the packfile Newly created objects with newly added history are still stored as single objects and periodic repacking is needed to maintain space efficiency The process of packing the repository can be very computationally costly By allowing objects to exist in the repository in a loose but quickly generated format Git allows the costly pack operation to be deferred until later when time matters less e g the end of a workday Git does periodic repacking automatically but manual repacking is also possible with the git gc command 61 For data integrity both the packfile and its index have an SHA 1 checksum 62 inside and the file name of the packfile also contains an SHA 1 checksum To check the integrity of a repository run the git fsck command 63 64 Another property of Git is that it snapshots directory trees of files The earliest systems for tracking versions of source code Source Code Control System SCCS and Revision Control System RCS worked on individual files and emphasized the space savings to be gained from interleaved deltas SCCS or delta encoding RCS the mostly similar versions Later revision control systems maintained this notion of a file having an identity across multiple revisions of a project However Torvalds rejected this concept 65 Consequently Git does not explicitly record file revision relationships at any level below the source code tree These implicit revision relationships have some significant consequences It is slightly more costly to examine the change history of one file than the whole project 66 To obtain a history of changes affecting a given file Git must walk the global history and then determine whether each change modified that file This method of examining history does however let Git produce with equal efficiency a single history showing the changes to an arbitrary set of files For example a subdirectory of the source tree plus an associated global header file is a very common case Renames are handled implicitly rather than explicitly A common complaint with CVS is that it uses the name of a file to identify its revision history so moving or renaming a file is not possible without either interrupting its history or renaming the history and thereby making the history inaccurate Most post CVS revision control systems solve this by giving a file a unique long lived name analogous to an inode number that survives renaming Git does not record such an identifier and this is claimed as an advantage 67 68 Source code files are sometimes split or merged or simply renamed 69 and recording this as a simple rename would freeze an inaccurate description of what happened in the immutable history Git addresses the issue by detecting renames while browsing the history of snapshots rather than recording it when making the snapshot 70 Briefly given a file in revision N a file of the same name in revision N 1 is its default ancestor However when there is no like named file in revision N 1 Git searches for a file that existed only in revision N 1 and is very similar to the new file However it does require more CPU intensive work every time the history is reviewed and several options to adjust the heuristics are available This mechanism does not always work sometimes a file that is renamed with changes in the same commit is read as a deletion of the old file and the creation of a new file Developers can work around this limitation by committing the rename and the changes separately Git implements several merging strategies a non default strategy can be selected at merge time 71 resolve the traditional three way merge algorithm recursive This is the default when pulling or merging one branch and is a variant of the three way merge algorithm When there are more than one common ancestors that can be used for a three way merge it creates a merged tree of the common ancestors and uses that as the reference tree for the three way merge This has been reported to result in fewer merge conflicts without causing mis merges by tests done on prior merge commits taken from Linux 2 6 kernel development history Also this can detect and handle merges involving renames Linus Torvalds 72 octopus This is the default when merging more than two heads Data structures edit Git s primitives are not inherently a source code management system Torvalds explains 73 In many ways you can just see git as a filesystem it s content addressable and it has a notion of versioning but I really designed it coming at the problem from the viewpoint of a filesystem person hey kernels is what I do and I actually have absolutely zero interest in creating a traditional SCM system From this initial design approach Git has developed the full set of features expected of a traditional SCM 48 with features mostly being created as needed then refined and extended over time nbsp Some data flows and storage levels in the Git revision control systemGit has two data structures a mutable index also called stage or cache that caches information about the working directory and the next revision to be committed and an immutable append only object database The index serves as a connection point between the object database and the working tree The object store contains five types of objects 74 63 A blob is the content of a file Blobs have no proper file name time stamps or other metadata a blob s name internally is a hash of its content 75 In git each blob is a version of a file in which is the file s data 76 A tree object is the equivalent of a directory It contains a list of file names 77 each with some type bits and a reference to a blob or tree object that is that file symbolic link or directory s contents These objects are a snapshot of the source tree In whole this comprises a Merkle tree meaning that only a single hash for the root tree is sufficient and actually used in commits to precisely pinpoint to the exact state of whole tree structures of any number of sub directories and files A commit object links tree objects together into history It contains the name of a tree object of the top level source directory a timestamp a log message and the names of zero or more parent commit objects 78 A tag object is a container that contains a reference to another object and can hold added meta data related to another object Most commonly it is used to store a digital signature of a commit object corresponding to a particular release of the data being tracked by Git 79 A packfile object collects various other objects into a zlib compressed bundle for compactness and ease of transport over network protocols 80 Each object is identified by a SHA 1 hash of its contents Git computes the hash and uses this value for the object s name The object is put into a directory matching the first two characters of its hash The rest of the hash is used as the file name for that object Git stores each revision of a file as a unique blob The relationships between the blobs can be found through examining the tree and commit objects Newly added objects are stored in their entirety using zlib compression This can consume a large amount of disk space quickly so objects can be combined into packs which use delta compression to save space storing blobs as their changes relative to other blobs Additionally git stores labels called refs short for references to indicate the locations of various commits They are stored in the reference database and are respectively 81 Heads branches Named references that are advanced automatically to the new commit when a commit is made on top of them HEAD A reserved head that will be compared against the working tree to create a commit Tags Like branch references but fixed to a particular commit Used to label important points in history References edit Every object in the Git database that is not referred to may be cleaned up by using a garbage collection command or automatically An object may be referenced by another object or an explicit reference Git knows different types of references The commands to create move and delete references vary git show ref lists all references Some types are heads refers to an object locally remotes refers to an object which exists in a remote repository stash refers to an object not yet committed meta e g a configuration in a bare repository user rights the refs meta config namespace was introduced retrospectively gets used by Gerrit 82 tags see above Implementations edit nbsp gitg is a graphical front end using GTK Git the main implementation in C is primarily developed on Linux although it also supports most major operating systems including the BSDs DragonFly BSD FreeBSD NetBSD and OpenBSD Solaris macOS and Windows 83 84 The first Windows port of Git was primarily a Linux emulation framework that hosts the Linux version Installing Git under Windows creates a similarly named Program Files directory containing the Mingw w64 port of the GNU Compiler Collection Perl 5 MSYS2 itself a fork of Cygwin a Unix like emulation environment for Windows and various other Windows ports or emulations of Linux utilities and libraries Currently native Windows builds of Git are distributed as 32 and 64 bit installers 85 The git official website currently maintains a build of Git for Windows still using the MSYS2 environment 86 The JGit implementation of Git is a pure Java software library designed to be embedded in any Java application JGit is used in the Gerrit code review tool and in EGit a Git client for the Eclipse IDE 87 Go git is an open source implementation of Git written in pure Go 88 It is currently used for backing projects as a SQL interface for Git code repositories 89 and providing encryption for Git 90 The Dulwich implementation of Git is a pure Python software component for Python 2 7 3 4 and 3 5 91 The libgit2 implementation of Git is an ANSI C software library with no other dependencies which can be built on multiple platforms including Windows Linux macOS and BSD 92 It has bindings for many programming languages including Ruby Python and Haskell 93 94 95 JS Git is a JavaScript implementation of a subset of Git 96 Git server edit nbsp Screenshot of Gitweb interface showing a commit diffAs Git is a distributed version control system it could be used as a server out of the box It is shipped with a built in command git daemon which starts a simple TCP server running on the Git protocol 97 98 Dedicated Git HTTP servers help amongst other features by adding access control displaying the contents of a Git repository via the web interfaces and managing multiple repositories Already existing Git repositories can be cloned and shared to be used by others as a centralized repo It can also be accessed via remote shell just by having the Git software installed and allowing a user to log in 99 Git servers typically listen on TCP port 9418 100 Open source edit Hosting the Git server using the Git Binary 101 Gerrit a Git server configurable to support code reviews and provide access via ssh an integrated Apache MINA or OpenSSH or an integrated Jetty web server Gerrit provides integration for LDAP Active Directory OpenID OAuth Kerberos GSSAPI X509 https client certificates With Gerrit 3 0 all configurations will be stored as Git repositories and no database is required to run Gerrit has a pull request feature implemented in its core but lacks a GUI for it Phabricator a spin off from Facebook As Facebook primarily uses Mercurial Git support is not as prominent 102 RhodeCode Community Edition CE supporting Git Mercurial and Subversion with an AGPLv3 license Kallithea supporting both Git and Mercurial developed in Python with GPL license External projects like gitolite 103 which provide scripts on top of Git software to provide fine grained access control There are several other FLOSS solutions for self hosting including Gogs 104 and Gitea a fork of Gogs both developed in Go language with MIT license Git server as a service edit See also Comparison of source code hosting facilities There are many offerings of Git repositories as a service The most popular are GitHub SourceForge Bitbucket and GitLab 38 17 18 19 20 Adoption editThe Eclipse Foundation reported in its annual community survey that as of May 2014 Git is now the most widely used source code management tool with 42 9 of professional software developers reporting that they use Git as their primary source control system 105 compared with 36 3 in 2013 32 in 2012 or for Git responses excluding use of GitHub 33 3 in 2014 30 3 in 2013 27 6 in 2012 and 12 8 in 2011 106 Open source directory Black Duck Open Hub reports a similar uptake among open source projects 107 Stack Overflow has included version control in their annual developer survey 108 in 2015 16 694 responses 109 2017 30 730 responses 110 2018 74 298 responses 111 and 2022 71 379 responses 15 Git was the overwhelming favorite of responding developers in these surveys reporting as high as 93 9 in 2022 Version control systems used by responding developers Name 2015 2017 2018 2022Git 69 3 69 2 87 2 93 9 Subversion 36 9 9 1 16 1 5 2 TFVC 12 2 7 3 10 9 ii Mercurial 7 9 1 9 3 6 1 1 CVS 4 2 ii ii ii Perforce 3 3 ii ii ii VSS ii 0 6 ii ii ClearCase ii 0 4 ii ii Zip file backups ii 2 0 7 9 ii Raw network sharing ii 1 7 7 9 ii Other 5 8 3 0 ii ii None 9 3 4 8 4 8 4 3 The UK IT jobs website itjobswatch co uk reports that as of late September 2016 29 27 of UK permanent software development job openings have cited Git 112 ahead of 12 17 for Microsoft Team Foundation Server 113 10 60 for Subversion 114 1 30 for Mercurial 115 and 0 48 for Visual SourceSafe 116 Extensions edit There are many Git extensions like Git LFS which started as an extension to Git in the GitHub community and is now widely used by other repositories Extensions are usually independently developed and maintained by different people but at some point in the future a widely used extension can be merged with Git Other open source Git extensions include git annex a distributed file synchronization system based on Git git flow a set of Git extensions to provide high level repository operations for Vincent Driessen s branching model git machete a repository organizer amp tool for automating rebase merge pull push operationsMicrosoft developed the Virtual File System for Git VFS for Git formerly Git Virtual File System or GVFS extension to handle the size of the Windows source code tree as part of their 2017 migration from Perforce VFS for Git allows cloned repositories to use placeholders whose contents are downloaded only once a file is accessed 117 Conventions editGit does not impose many restrictions on how it should be used but some conventions are adopted in order to organize histories especially those which require the cooperation of many contributors The master branch is created by default with git init 76 118 and is often used as the branch that other changes are merged into 119 Correspondingly the default name of the upstream remote is origin 120 and so the name of the default remote branch is origin master The use of master as the default branch name is not universally true repositories created in GitHub and GitLab initialize with a main branch instead of master 121 122 though the default can be changed by the user Pushed commits should usually not be overwritten but should rather be reverted 123 a commit is made on top which reverses the changes to an earlier commit This prevents shared new commits based on shared commits from being invalid because the commit on which they are based does not exist in the remote If the commits contain sensitive information they should be removed which involves a more complex procedure to rewrite history The git flow 124 workflow and naming conventions are often adopted to distinguish feature specific unstable histories feature unstable shared histories develop production ready histories main and emergency patches to released products hotfix Pull requests are not a feature of git but are commonly provided by git cloud services A pull request is a request by one user to merge a branch of their repository fork into another repository sharing the same history called the upstream remote 125 126 The underlying function of a pull request is no different than that of an administrator of a repository pulling changes from another remote the repository that is the source of the pull request However the pull request itself is a ticket managed by the hosting server which initiates scripts to perform these actions it is not a feature of git SCM Security editGit does not provide access control mechanisms but was designed for operation with other tools that specialize in access control 127 On 17 December 2014 an exploit was found affecting the Windows and macOS versions of the Git client An attacker could perform arbitrary code execution on a target computer with Git installed by creating a malicious Git tree directory named git a directory in Git repositories that stores all the data of the repository in a different case such as GIT or Git needed because Git does not allow the all lowercase version of git to be created manually with malicious files in the git hooks subdirectory a folder with executable files that Git runs on a repository that the attacker made or on a repository that the attacker can modify If a Windows or Mac user pulls downloads a version of the repository with the malicious directory then switches to that directory the git directory will be overwritten due to the case insensitive trait of the Windows and Mac filesystems and the malicious executable files in git hooks may be run which results in the attacker s commands being executed An attacker could also modify the git config configuration file which allows the attacker to create malicious Git aliases aliases for Git commands or external commands or modify extant aliases to execute malicious commands when run The vulnerability was patched in version 2 2 1 of Git released on 17 December 2014 and announced the next day 128 129 Git version 2 6 1 released on 29 September 2015 contained a patch for a security vulnerability CVE 2015 7545 130 that allowed arbitrary code execution 131 The vulnerability was exploitable if an attacker could convince a victim to clone a specific URL as the arbitrary commands were embedded in the URL itself 132 An attacker could use the exploit via a man in the middle attack if the connection was unencrypted 132 as they could redirect the user to a URL of their choice Recursive clones were also vulnerable since they allowed the controller of a repository to specify arbitrary URLs via the gitmodules file 132 Git uses SHA 1 hashes internally Linus Torvalds has responded that the hash was mostly to guard against accidental corruption and the security a cryptographically secure hash gives was just an accidental side effect with the main security being signing elsewhere 133 134 Since a demonstration of the SHAttered attack against git in 2017 git was modified to use a SHA 1 variant resistant to this attack A plan for hash function transition is being written since February 2020 135 Trademark edit Git is a registered word trademark of Software Freedom Conservancy under US500000085961336 since 2015 02 03 See also edit nbsp Free and open source software portal nbsp Linux portal nbsp Internet portalComparison of version control software Comparison of source code hosting facilities List of version control softwareNotes edit GPL 2 0 only since 2005 04 11 Some parts under compatible licenses such as LGPLv2 1 6 a b c d e f g h i j k l m n o p q r s Not listed as an option in this surveyCitations edit Initial revision of git the information manager from hell GitHub 8 April 2005 Archived from the original on 16 November 2015 Retrieved 20 December 2015 Commit Graph GitHub 8 June 2016 Archived from the original on 20 January 2016 Retrieved 19 December 2015 Junio C Hamano 20 November 2023 ANNOUNCE Git v2 43 0 Retrieved 21 November 2023 Git website Archived from the original on 9 June 2022 Retrieved 9 June 2022 Git Source Code Mirror GitHub Archived from the original on 3 June 2022 Retrieved 9 June 2022 Git s LGPL license at github com GitHub 20 May 2011 Archived from the original on 11 April 2016 Retrieved 12 October 2014 Git s GPL license at github com GitHub 18 January 2010 Archived from the original on 11 April 2016 Retrieved 12 October 2014 Tech Talk Linus Torvalds on git at 00 01 30 Archived from the original on 20 December 2015 Retrieved 20 July 2014 via YouTube Chacon amp Straub 2014 pp 29 31 a b Torvalds Linus 7 April 2005 Re Kernel SCM saga linux kernel Mailing list Archived from the original on 1 July 2019 Retrieved 3 February 2017 So I m writing some scripts to try to track things a whole lot faster a b Torvalds Linus 10 June 2007 Re fatal serious inflate inconsistency git Mailing list a b c d Linus Torvalds 3 May 2007 Google tech talk Linus Torvalds on git Event occurs at 02 30 Archived from the original on 28 May 2007 Retrieved 16 May 2007 a b A Short History of Git Pro Git 2nd ed Apress 2014 Archived from the original on 25 December 2015 Retrieved 26 December 2015 Chacon Scott 24 December 2014 Pro Git 2nd ed New York NY Apress pp 29 30 ISBN 978 1 4842 0077 3 Archived from the original on 25 December 2015 a b Stack Overflow Developer Survey 2022 Stack Overflow Retrieved 4 August 2022 Krill Paul 28 September 2016 Enterprise repo wars GitHub vs GitLab vs Bitbucket InfoWorld Retrieved 2 February 2020 a b github com Competitive Analysis Marketing Mix and Traffic Alexa Archived from the original on 31 March 2013 Retrieved 2 February 2020 a b sourceforge net Competitive Analysis Marketing Mix and Traffic Alexa Archived from the original on 20 October 2020 Retrieved 2 February 2020 a b bitbucket org Competitive Analysis Marketing Mix and Traffic Alexa Archived from the original on 23 June 2017 Retrieved 2 February 2020 a b gitlab com Competitive Analysis Marketing Mix and Traffic Alexa Archived from the original on 30 November 2017 Retrieved 2 February 2020 Brown Zack 27 July 2018 A Git Origin Story Linux Journal Linux Journal Archived from the original on 13 April 2020 Retrieved 28 May 2020 BitKeeper and Linux The end of the road Linux com 11 April 2005 Retrieved 18 May 2023 McAllister Neil 2 May 2005 Linus Torvalds BitKeeper blunder InfoWorld Archived from the original on 26 August 2015 Retrieved 8 September 2015 a b Torvalds Linus 27 February 2007 Re Trivia When did git self host git Mailing list Torvalds Linus 6 April 2005 Kernel SCM saga linux kernel Mailing list Torvalds Linus 17 April 2005 First ever real kernel git merge git Mailing list Mackall Matt 29 April 2005 Mercurial 0 4b vs git patchbomb benchmark git Mailing list Torvalds Linus 17 June 2005 Linux 2 6 12 git commits head Mailing list Torvalds Linus 27 July 2005 Meet the new maintainer git Mailing list Hamano Junio C 21 December 2005 Announce Git 1 0 0 git Mailing list GitFaq Why the Git name Git or cz Archived from the original on 23 July 2012 Retrieved 14 July 2012 After controversy Torvalds begins work on git PC World 14 July 2012 Archived from the original on 1 February 2011 Torvalds seemed aware that his decision to drop BitKeeper would also be controversial When asked why he called the new software git British slang meaning a rotten person he said I m an egotistical bastard so I name all my projects after myself First Linux now git git 1 Manual Page Archived from the original on 21 June 2012 Retrieved 21 July 2012 Initial revision of git the information manager from hell git git e83c516 GitHub Archived from the original on 8 October 2017 Retrieved 21 January 2016 Tags GitHub Archived from the original on 29 September 2021 Retrieved 28 January 2022 Highlights from Git 2 23 The GitHub Blog 16 August 2019 Retrieved 14 November 2023 Highlights from Git 2 25 The GitHub Blog 13 January 2020 Archived from the original on 22 March 2021 Retrieved 27 November 2020 A sparse checkout is nothing more than a list of file path patterns that Git should attempt to populate in your working copy when checking out the contents of your repository Effectively it works like a gitignore except it acts on the contents of your working copy rather than on your index a b Highlights from Git 2 26 The GitHub Blog 22 March 2020 Archived from the original on 22 March 2021 Retrieved 25 November 2020 You may remember when Git introduced a new version of its network fetch protocol way back in 2018 That protocol is now used by default in 2 26 so let s refresh ourselves on what that means The biggest problem with the old protocol is that the server would immediately list all of the branches tags and other references in the repository before the client had a chance to send anything For some repositories this could mean sending megabytes of extra data when the client really only wanted to know about the master branch The new protocol starts with the client request and provides a way for the client to tell the server which references it s interested in Fetching a single branch will only ask about that branch while most clones will only ask about branches and tags This might seem like everything but server repositories may store other references such as the head of every pull request opened in the repository since its creation Now fetches from large repositories improve in speed especially when the fetch itself is small which makes the cost of the initial reference advertisement more expensive relatively speaking And the best part is that you won t need to do anything Due to some clever design any client that speaks the new protocol can work seamlessly with both old and new servers falling back to the original protocol if the server doesn t support it The only reason for the delay between introducing the protocol and making it the default was to let early adopters discover any bugs Highlights from Git 2 28 The GitHub Blog 27 July 2020 Archived from the original on 22 March 2021 Retrieved 25 November 2020 Highlights from Git 2 29 The GitHub Blog 19 October 2020 Archived from the original on 22 March 2021 Retrieved 25 November 2020 Git 2 30 Release Notes Git Downloads 27 December 2020 Archived from the original on 22 March 2021 Retrieved 27 December 2020 Git 2 31 Release Notes Git Downloads 3 April 2021 Retrieved 3 April 2021 Highlights from Git 2 31 The GitHub Blog 15 March 2021 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Salary for Git Distributed Version Control System Skills Itjobswatch co uk Archived from the original on 8 October 2016 Retrieved 30 September 2016 Team Foundation Server Jobs Average Salary for Microsoft Team Foundation Server TFS Skills Itjobswatch co uk Archived from the original on 29 October 2016 Retrieved 30 September 2016 Subversion Jobs Average Salary for Apache Subversion SVN Skills Itjobswatch co uk Archived from the original on 25 October 2016 Retrieved 30 September 2016 Mercurial Jobs Average Salary for Mercurial Skills Itjobswatch co uk Archived from the original on 23 September 2016 Retrieved 30 September 2016 VSS SourceSafe Jobs Average Salary for Microsoft Visual SourceSafe VSS Skills Itjobswatch co uk Archived from the original on 29 October 2016 Retrieved 30 September 2016 Windows switch to Git almost complete 8 500 commits and 1 760 builds each day Ars Technica 24 May 2017 Archived from the original on 24 May 2017 Retrieved 24 May 2017 git init Git Archived from the original on 15 March 2022 Git Branches in a Nutshell Git Archived from the original on 20 December 2020 Retrieved 15 June 2020 The master branch in Git is not a special branch It is exactly like any other branch The only reason nearly every repository has one is that the git init command creates it by default and most people don t bother to change it Chacon amp Straub 2014 pp 103 109 github renaming GitHub 4 December 2020 retrieved 4 December 2020 Default branch name for new repositories now main GitLab 22 June 2021 retrieved 22 June 2021 Git Revert Atlassian Git Tutorial Atlassian Reverting has two important advantages over resetting First it doesn t change the project history which makes it a safe operation for commits that have already been published to a shared repository Gitflow Workflow Atlassian Git Tutorial Atlassian Retrieved 15 June 2020 Chacon amp Straub 2014 pp 170 174 Forking Workflow Atlassian Git Tutorial Atlassian Retrieved 15 June 2020 Git repository access control Archived from the original on 14 September 2016 Retrieved 6 September 2016 Pettersen Tim 20 December 2014 Securing your Git server against CVE 2014 9390 Archived from the original on 24 December 2014 Retrieved 22 December 2014 Hamano J C 18 December 2014 Announce Git v2 2 1 and updates to older maintenance tracks Newsgroup gmane linux kernel Archived from the original on 19 December 2014 Retrieved 22 December 2014 CVE 2015 7545 15 December 2015 Archived from the original on 26 December 2015 Retrieved 26 December 2015 Git 2 6 1 GitHub 29 September 2015 Archived from the original on 11 April 2016 Retrieved 26 December 2015 a b c Blake Burkhart et al 5 October 2015 Re CVE Request git Archived from the original on 27 December 2015 Retrieved 26 December 2015 hash How safe are signed git tags Only as safe as SHA 1 or somehow safer Information Security Stack Exchange 22 September 2014 Archived from the original on 24 June 2016 Why does Git use a cryptographic hash function Stack Overflow 1 March 2015 Archived from the original on 1 July 2016 Git hash function transition Documentation Git References editChacon Scott 24 December 2014 Pro Git 2nd ed New York NY Apress ISBN 978 1 4842 0077 3 Archived from the original on 25 December 2015 External links edit nbsp Wikimedia Commons has media related to Git nbsp Wikibooks has a book on the topic of Git Official website nbsp Git at Open Hub Retrieved from https en wikipedia org w index php title Git amp oldid 1187485593, wikipedia, wiki, book, books, library,

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