2 .\" Copyright (c) 2018 Stefan Sperling <stsp@openbsd.org>
4 .\" Permission to use, copy, modify, and distribute this software for any
5 .\" purpose with or without fee is hereby granted, provided that the above
6 .\" copyright notice and this permission notice appear in all copies.
8 .\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
9 .\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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21 .Nd Git repository format
23 A Git repository stores a series of versioned snapshots of a file hierarchy.
24 Conceptually, the repository's data model is a directed acyclic graph which
25 contains three types of objects as nodes:
28 The content of tracked files is stored in objects of type
33 object points to any number of such blobs, and also to other trees in
34 order to represent a hierarchy of files and directories.
38 object points to the root element of one tree, and thus records the
39 state of this entire tree as a snapshot.
40 Commit objects are chained together to form lines of version control history.
41 Most commits have just one successor commit, but commits may be succeeded by
42 an arbitrary number of subsequent commits so that diverging lines of version
43 control history, known as
46 A commit which precedes another commit is referred to as that other commit's
48 A commit with multiple parents unites disparate lines of history and is
53 Each object is identified by a SHA1 hash calculated over both the object's
54 header and the data stored in the object.
56 Loose objects are stored as individual files beneath the directory
58 spread across 256 sub-directories named after the 256 possible hexadecimal
59 values of the first byte of an object identifier.
60 The name of the loose object file corresponds to the remaining hexadecimal
61 byte values of the object's identifier.
63 A loose object file begins with a header which specifies the type of object
64 as an ASCII string, followed by an ASCII space character, followed by the
65 object data's size encoded as an ASCII number string.
66 The header is terminated by a
68 character, and the remainder of the file contains object data.
69 Loose objects files are compressed with
72 Multiple objects can be bundled in a
74 for better disk space efficiency and increased run-time performance.
75 The pack file format knows two additional types of objects in addition
76 to blobs, trees, and commits:
78 .It Offset Delta Objects
79 This object is represented as a delta against another object in the
81 This other object is referred to by its offset in the pack file.
82 .It Reference Delta Objects
83 This object is represented as a delta against another object in the
85 The other object is referred to by its SHA1 object identifier.
88 Pack files are self-contained and may not refer to loose objects or
89 objects stored in other pack files.
90 Deltified objects may refer to other deltified objects as their delta base,
91 forming chains of deltas.
92 The ultimate base of a delta chain must be an object of the same type as
93 the original object which is stored in deltified form.
95 Each pack file is accompanied by a corresponding
97 file, which lists the IDs and offsets of all objects contained in the
100 .Bl -tag -width packed-refs -compact
102 A reference to the current head commit of the Git work tree.
103 In bare repositories, this files serves as a default reference.
105 Reference to original head commit.
106 Set by some Git operations.
108 Reference to a branch tip commit most recently fetched from another repository.
110 Legacy directory used by the deprectated Gogito Git interface.
112 Git configuration file. See
115 A human-readable description of the repository.
117 This directory contains hook scripts to run when certain events occur.
119 The file index used by
121 This file is not used by
127 Various configuration items.
129 Directory where reflogs are stored.
131 Loose and packed objects are stored in this directory.
133 A file which stores references.
134 Corresponding on-disk references take precedence over those stored here.
136 The default directory to store references in.
139 A typical Git repository exposes a work tree which allows the user to make
140 changes to versioned files and create new commits.
141 When a Git work tree is present, the actual repository data is stored in a
143 subfolder of the repository's root directory.
144 A Git repository without a work tree is known as a
148 does not make use of Git's work tree and treats every repository as if it
156 The Git repository format was initially designed by Linus Torvalds in 2005
157 and has since been extended by various people involved in the development
158 of the Git version control system.
