1GITSUBMODULES(7)                  Git Manual                  GITSUBMODULES(7)
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NAME

6       gitsubmodules - mounting one repository inside another
7

SYNOPSIS

9       .gitmodules, $GIT_DIR/config
10
11       git submodule
12       git <command> --recurse-submodules
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14

DESCRIPTION

16       A submodule is a repository embedded inside another repository. The
17       submodule has its own history; the repository it is embedded in is
18       called a superproject.
19
20       On the filesystem, a submodule usually (but not always - see FORMS
21       below) consists of (i) a Git directory located under the
22       $GIT_DIR/modules/ directory of its superproject, (ii) a working
23       directory inside the superproject’s working directory, and a .git file
24       at the root of the submodule’s working directory pointing to (i).
25
26       Assuming the submodule has a Git directory at $GIT_DIR/modules/foo/ and
27       a working directory at path/to/bar/, the superproject tracks the
28       submodule via a gitlink entry in the tree at path/to/bar and an entry
29       in its .gitmodules file (see gitmodules(5)) of the form
30       submodule.foo.path = path/to/bar.
31
32       The gitlink entry contains the object name of the commit that the
33       superproject expects the submodule’s working directory to be at.
34
35       The section submodule.foo.* in the .gitmodules file gives additional
36       hints to Git’s porcelain layer. For example, the submodule.foo.url
37       setting specifies where to obtain the submodule.
38
39       Submodules can be used for at least two different use cases:
40
41        1. Using another project while maintaining independent history.
42           Submodules allow you to contain the working tree of another project
43           within your own working tree while keeping the history of both
44           projects separate. Also, since submodules are fixed to an arbitrary
45           version, the other project can be independently developed without
46           affecting the superproject, allowing the superproject project to
47           fix itself to new versions only when desired.
48
49        2. Splitting a (logically single) project into multiple repositories
50           and tying them back together. This can be used to overcome current
51           limitations of Git’s implementation to have finer grained access:
52
53           ·   Size of the Git repository: In its current form Git scales up
54               poorly for large repositories containing content that is not
55               compressed by delta computation between trees. For example, you
56               can use submodules to hold large binary assets and these
57               repositories can be shallowly cloned such that you do not have
58               a large history locally.
59
60           ·   Transfer size: In its current form Git requires the whole
61               working tree present. It does not allow partial trees to be
62               transferred in fetch or clone. If the project you work on
63               consists of multiple repositories tied together as submodules
64               in a superproject, you can avoid fetching the working trees of
65               the repositories you are not interested in.
66
67           ·   Access control: By restricting user access to submodules, this
68               can be used to implement read/write policies for different
69               users.
70

THE CONFIGURATION OF SUBMODULES

72       Submodule operations can be configured using the following mechanisms
73       (from highest to lowest precedence):
74
75       ·   The command line for those commands that support taking submodules
76           as part of their pathspecs. Most commands have a boolean flag
77           --recurse-submodules which specify whether to recurse into
78           submodules. Examples are grep and checkout. Some commands take
79           enums, such as fetch and push, where you can specify how submodules
80           are affected.
81
82       ·   The configuration inside the submodule. This includes
83           $GIT_DIR/config in the submodule, but also settings in the tree
84           such as a .gitattributes or .gitignore files that specify behavior
85           of commands inside the submodule.
86
87           For example an effect from the submodule’s .gitignore file would be
88           observed when you run git status --ignore-submodules=none in the
89           superproject. This collects information from the submodule’s
90           working directory by running status in the submodule while paying
91           attention to the .gitignore file of the submodule.
92
93           The submodule’s $GIT_DIR/config file would come into play when
94           running git push --recurse-submodules=check in the superproject, as
95           this would check if the submodule has any changes not published to
96           any remote. The remotes are configured in the submodule as usual in
97           the $GIT_DIR/config file.
98
99       ·   The configuration file $GIT_DIR/config in the superproject. Git
100           only recurses into active submodules (see "ACTIVE SUBMODULES"
101           section below).
102
103           If the submodule is not yet initialized, then the configuration
104           inside the submodule does not exist yet, so where to obtain the
105           submodule from is configured here for example.
106
107       ·   The .gitmodules file inside the superproject. A project usually
108           uses this file to suggest defaults for the upstream collection of
109           repositories for the mapping that is required between a submodule’s
110           name and its path.
111
112           This file mainly serves as the mapping between the name and path of
113           submodules in the superproject, such that the submodule’s Git
114           directory can be located.
115
116           If the submodule has never been initialized, this is the only place
117           where submodule configuration is found. It serves as the last
118           fallback to specify where to obtain the submodule from.
119

FORMS

121       Submodules can take the following forms:
122
123       ·   The basic form described in DESCRIPTION with a Git directory, a
124           working directory, a gitlink, and a .gitmodules entry.
125
126       ·   "Old-form" submodule: A working directory with an embedded .git
127           directory, and the tracking gitlink and .gitmodules entry in the
128           superproject. This is typically found in repositories generated
129           using older versions of Git.
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131           It is possible to construct these old form repositories manually.
132
133           When deinitialized or deleted (see below), the submodule’s Git
134           directory is automatically moved to $GIT_DIR/modules/<name>/ of the
135           superproject.
136
137       ·   Deinitialized submodule: A gitlink, and a .gitmodules entry, but no
138           submodule working directory. The submodule’s Git directory may be
139           there as after deinitializing the Git directory is kept around. The
140           directory which is supposed to be the working directory is empty
141           instead.
142
143           A submodule can be deinitialized by running git submodule deinit.
144           Besides emptying the working directory, this command only modifies
145           the superproject’s $GIT_DIR/config file, so the superproject’s
146           history is not affected. This can be undone using git submodule
147           init.
148
149       ·   Deleted submodule: A submodule can be deleted by running git rm
150           <submodule path> && git commit. This can be undone using git
151           revert.
152
153           The deletion removes the superproject’s tracking data, which are
154           both the gitlink entry and the section in the .gitmodules file. The
155           submodule’s working directory is removed from the file system, but
156           the Git directory is kept around as it to make it possible to
157           checkout past commits without requiring fetching from another
158           repository.
159
160           To completely remove a submodule, manually delete
161           $GIT_DIR/modules/<name>/.
162

ACTIVE SUBMODULES

164       A submodule is considered active,
165
166        1. if submodule.<name>.active is set to true
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168           or
169
170        2. if the submodule’s path matches the pathspec in submodule.active
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172           or
173
174        3. if submodule.<name>.url is set.
175
176       and these are evaluated in this order.
177
178       For example:
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180           [submodule "foo"]
181             active = false
182             url = https://example.org/foo
183           [submodule "bar"]
184             active = true
185             url = https://example.org/bar
186           [submodule "baz"]
187             url = https://example.org/baz
188
189       In the above config only the submodule bar and baz are active, bar due
190       to (1) and baz due to (3). foo is inactive because (1) takes precedence
191       over (3)
192
193       Note that (3) is a historical artefact and will be ignored if the (1)
194       and (2) specify that the submodule is not active. In other words, if we
195       have a submodule.<name>.active set to false or if the submodule’s path
196       is excluded in the pathspec in submodule.active, the url doesn’t matter
197       whether it is present or not. This is illustrated in the example that
198       follows.
199
200           [submodule "foo"]
201             active = true
202             url = https://example.org/foo
203           [submodule "bar"]
204             url = https://example.org/bar
205           [submodule "baz"]
206             url = https://example.org/baz
207           [submodule "bob"]
208             ignore = true
209           [submodule]
210             active = b*
211             active = :(exclude) baz
212
213       In here all submodules except baz (foo, bar, bob) are active. foo due
214       to its own active flag and all the others due to the submodule active
215       pathspec, which specifies that any submodule starting with b except baz
216       are also active, regardless of the presence of the .url field.
217

WORKFLOW FOR A THIRD PARTY LIBRARY

219           # add a submodule
220           git submodule add <url> <path>
221
222           # occasionally update the submodule to a new version:
223           git -C <path> checkout <new version>
224           git add <path>
225           git commit -m "update submodule to new version"
226
227           # See the list of submodules in a superproject
228           git submodule status
229
230           # See FORMS on removing submodules
231

WORKFLOW FOR AN ARTIFICIALLY SPLIT REPO

233           # Enable recursion for relevant commands, such that
234           # regular commands recurse into submodules by default
235           git config --global submodule.recurse true
236
237           # Unlike the other commands below clone still needs
238           # its own recurse flag:
239           git clone --recurse <URL> <directory>
240           cd <directory>
241
242           # Get to know the code:
243           git grep foo
244           git ls-files
245
246           # Get new code
247           git fetch
248           git pull --rebase
249
250           # change worktree
251           git checkout
252           git reset
253

IMPLEMENTATION DETAILS

255       When cloning or pulling a repository containing submodules the
256       submodules will not be checked out by default; You can instruct clone
257       to recurse into submodules. The init and update subcommands of git
258       submodule will maintain submodules checked out and at an appropriate
259       revision in your working tree. Alternatively you can set
260       submodule.recurse to have checkout recursing into submodules.
261

SEE ALSO

263       git-submodule(1), gitmodules(5).
264

GIT

266       Part of the git(1) suite
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270Git 2.24.1                        12/10/2019                  GITSUBMODULES(7)
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