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1 | gitsubmodules(7) |
2 | ================ | |
3 | ||
4 | NAME | |
5 | ---- | |
6 | gitsubmodules - mounting one repository inside another | |
7 | ||
8 | SYNOPSIS | |
9 | -------- | |
10 | .gitmodules, $GIT_DIR/config | |
11 | ------------------ | |
12 | git submodule | |
13 | git <command> --recurse-submodules | |
14 | ------------------ | |
15 | ||
16 | DESCRIPTION | |
17 | ----------- | |
18 | ||
19 | A submodule is a repository embedded inside another repository. | |
20 | The submodule has its own history; the repository it is embedded | |
21 | in is called a superproject. | |
22 | ||
23 | On the filesystem, a submodule usually (but not always - see FORMS below) | |
24 | consists of (i) a Git directory located under the `$GIT_DIR/modules/` | |
25 | directory of its superproject, (ii) a working directory inside the | |
26 | superproject's working directory, and a `.git` file at the root of | |
27 | the submodule’s working directory pointing to (i). | |
28 | ||
29 | Assuming the submodule has a Git directory at `$GIT_DIR/modules/foo/` | |
30 | and a working directory at `path/to/bar/`, the superproject tracks the | |
31 | submodule via a `gitlink` entry in the tree at `path/to/bar` and an entry | |
32 | in its `.gitmodules` file (see linkgit:gitmodules[5]) of the form | |
33 | `submodule.foo.path = path/to/bar`. | |
34 | ||
35 | The `gitlink` entry contains the object name of the commit that the | |
36 | superproject expects the submodule’s working directory to be at. | |
37 | ||
38 | The section `submodule.foo.*` in the `.gitmodules` file gives additional | |
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39 | hints to Git's porcelain layer. For example, the `submodule.foo.url` |
40 | setting specifies where to obtain the submodule. | |
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41 | |
42 | Submodules can be used for at least two different use cases: | |
43 | ||
44 | 1. Using another project while maintaining independent history. | |
45 | Submodules allow you to contain the working tree of another project | |
46 | within your own working tree while keeping the history of both | |
47 | projects separate. Also, since submodules are fixed to an arbitrary | |
48 | version, the other project can be independently developed without | |
49 | affecting the superproject, allowing the superproject project to | |
50 | fix itself to new versions only when desired. | |
51 | ||
52 | 2. Splitting a (logically single) project into multiple | |
53 | repositories and tying them back together. This can be used to | |
4f73a7f1 | 54 | overcome current limitations of Git's implementation to have |
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55 | finer grained access: |
56 | ||
4f73a7f1 | 57 | * Size of the Git repository: |
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58 | In its current form Git scales up poorly for large repositories containing |
59 | content that is not compressed by delta computation between trees. | |
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60 | For example, you can use submodules to hold large binary assets |
61 | and these repositories can be shallowly cloned such that you do not | |
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62 | have a large history locally. |
63 | * Transfer size: | |
64 | In its current form Git requires the whole working tree present. It | |
65 | does not allow partial trees to be transferred in fetch or clone. | |
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66 | If the project you work on consists of multiple repositories tied |
67 | together as submodules in a superproject, you can avoid fetching the | |
68 | working trees of the repositories you are not interested in. | |
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69 | * Access control: |
70 | By restricting user access to submodules, this can be used to implement | |
71 | read/write policies for different users. | |
72 | ||
73 | The configuration of submodules | |
74 | ------------------------------- | |
75 | ||
76 | Submodule operations can be configured using the following mechanisms | |
77 | (from highest to lowest precedence): | |
78 | ||
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79 | * The command line for those commands that support taking submodules |
80 | as part of their pathspecs. Most commands have a boolean flag | |
81 | `--recurse-submodules` which specify whether to recurse into submodules. | |
82 | Examples are `grep` and `checkout`. | |
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83 | Some commands take enums, such as `fetch` and `push`, where you can |
84 | specify how submodules are affected. | |
85 | ||
86 | * The configuration inside the submodule. This includes `$GIT_DIR/config` | |
87 | in the submodule, but also settings in the tree such as a `.gitattributes` | |
88 | or `.gitignore` files that specify behavior of commands inside the | |
89 | submodule. | |
90 | + | |
91 | For example an effect from the submodule's `.gitignore` file | |
92 | would be observed when you run `git status --ignore-submodules=none` in | |
93 | the superproject. This collects information from the submodule's working | |
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94 | directory by running `status` in the submodule while paying attention |
95 | to the `.gitignore` file of the submodule. | |
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96 | + |
97 | The submodule's `$GIT_DIR/config` file would come into play when running | |
98 | `git push --recurse-submodules=check` in the superproject, as this would | |
99 | check if the submodule has any changes not published to any remote. The | |
100 | remotes are configured in the submodule as usual in the `$GIT_DIR/config` | |
101 | file. | |
102 | ||
103 | * The configuration file `$GIT_DIR/config` in the superproject. | |
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104 | Git only recurses into active submodules (see "ACTIVE SUBMODULES" |
105 | section below). | |
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106 | + |
107 | If the submodule is not yet initialized, then the configuration | |
4f73a7f1 | 108 | inside the submodule does not exist yet, so where to |
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109 | obtain the submodule from is configured here for example. |
110 | ||
4f73a7f1 | 111 | * The `.gitmodules` file inside the superproject. A project usually |
d4803455 | 112 | uses this file to suggest defaults for the upstream collection |
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113 | of repositories for the mapping that is required between a |
114 | submodule's name and its path. | |
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116 | This file mainly serves as the mapping between the name and path of submodules |
117 | in the superproject, such that the submodule's Git directory can be | |
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118 | located. |
119 | + | |
120 | If the submodule has never been initialized, this is the only place | |
121 | where submodule configuration is found. It serves as the last fallback | |
122 | to specify where to obtain the submodule from. | |
123 | ||
124 | FORMS | |
125 | ----- | |
126 | ||
127 | Submodules can take the following forms: | |
128 | ||
129 | * The basic form described in DESCRIPTION with a Git directory, | |
130 | a working directory, a `gitlink`, and a `.gitmodules` entry. | |
131 | ||
132 | * "Old-form" submodule: A working directory with an embedded | |
133 | `.git` directory, and the tracking `gitlink` and `.gitmodules` entry in | |
134 | the superproject. This is typically found in repositories generated | |
135 | using older versions of Git. | |
136 | + | |
137 | It is possible to construct these old form repositories manually. | |
138 | + | |
139 | When deinitialized or deleted (see below), the submodule’s Git | |
140 | directory is automatically moved to `$GIT_DIR/modules/<name>/` | |
141 | of the superproject. | |
142 | ||
143 | * Deinitialized submodule: A `gitlink`, and a `.gitmodules` entry, | |
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144 | but no submodule working directory. The submodule’s Git directory |
145 | may be there as after deinitializing the Git directory is kept around. | |
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146 | The directory which is supposed to be the working directory is empty instead. |
147 | + | |
148 | A submodule can be deinitialized by running `git submodule deinit`. | |
149 | Besides emptying the working directory, this command only modifies | |
150 | the superproject’s `$GIT_DIR/config` file, so the superproject’s history | |
151 | is not affected. This can be undone using `git submodule init`. | |
152 | ||
153 | * Deleted submodule: A submodule can be deleted by running | |
154 | `git rm <submodule path> && git commit`. This can be undone | |
155 | using `git revert`. | |
156 | + | |
157 | The deletion removes the superproject’s tracking data, which are | |
158 | both the `gitlink` entry and the section in the `.gitmodules` file. | |
159 | The submodule’s working directory is removed from the file | |
160 | system, but the Git directory is kept around as it to make it | |
161 | possible to checkout past commits without requiring fetching | |
162 | from another repository. | |
163 | + | |
164 | To completely remove a submodule, manually delete | |
165 | `$GIT_DIR/modules/<name>/`. | |
166 | ||
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167 | ACTIVE SUBMODULES |
168 | ----------------- | |
169 | ||
170 | A submodule is considered active, | |
171 | ||
172 | (a) if `submodule.<name>.active` is set to `true` | |
173 | or | |
174 | (b) if the submodule's path matches the pathspec in `submodule.active` | |
175 | or | |
176 | (c) if `submodule.<name>.url` is set. | |
177 | ||
178 | and these are evaluated in this order. | |
179 | ||
180 | For example: | |
181 | ||
182 | [submodule "foo"] | |
183 | active = false | |
184 | url = https://example.org/foo | |
185 | [submodule "bar"] | |
186 | active = true | |
187 | url = https://example.org/bar | |
188 | [submodule "baz"] | |
189 | url = https://example.org/baz | |
190 | ||
191 | In the above config only the submodule 'bar' and 'baz' are active, | |
192 | 'bar' due to (a) and 'baz' due to (c). 'foo' is inactive because | |
193 | (a) takes precedence over (c) | |
194 | ||
195 | Note that (c) is a historical artefact and will be ignored if the | |
196 | (a) and (b) specify that the submodule is not active. In other words, | |
197 | if we have an `submodule.<name>.active` set to `false` or if the | |
198 | submodule's path is excluded in the pathspec in `submodule.active`, the | |
199 | url doesn't matter whether it is present or not. This is illustrated in | |
200 | the example that follows. | |
201 | ||
202 | [submodule "foo"] | |
203 | active = true | |
204 | url = https://example.org/foo | |
205 | [submodule "bar"] | |
206 | url = https://example.org/bar | |
207 | [submodule "baz"] | |
208 | url = https://example.org/baz | |
209 | [submodule "bob"] | |
210 | ignore = true | |
211 | [submodule] | |
212 | active = b* | |
213 | active = :(exclude) baz | |
214 | ||
215 | In here all submodules except 'baz' (foo, bar, bob) are active. | |
216 | 'foo' due to its own active flag and all the others due to the | |
217 | submodule active pathspec, which specifies that any submodule | |
218 | starting with 'b' except 'baz' are also active, regardless of the | |
219 | presence of the .url field. | |
220 | ||
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221 | Workflow for a third party library |
222 | ---------------------------------- | |
223 | ||
224 | # add a submodule | |
225 | git submodule add <url> <path> | |
226 | ||
227 | # occasionally update the submodule to a new version: | |
228 | git -C <path> checkout <new version> | |
229 | git add <path> | |
230 | git commit -m "update submodule to new version" | |
231 | ||
232 | # See the list of submodules in a superproject | |
233 | git submodule status | |
234 | ||
235 | # See FORMS on removing submodules | |
236 | ||
237 | ||
238 | Workflow for an artificially split repo | |
239 | -------------------------------------- | |
240 | ||
241 | # Enable recursion for relevant commands, such that | |
242 | # regular commands recurse into submodules by default | |
243 | git config --global submodule.recurse true | |
244 | ||
245 | # Unlike the other commands below clone still needs | |
246 | # its own recurse flag: | |
247 | git clone --recurse <URL> <directory> | |
248 | cd <directory> | |
249 | ||
250 | # Get to know the code: | |
251 | git grep foo | |
252 | git ls-files | |
253 | ||
254 | # Get new code | |
255 | git fetch | |
256 | git pull --rebase | |
257 | ||
258 | # change worktree | |
259 | git checkout | |
260 | git reset | |
261 | ||
262 | Implementation details | |
263 | ---------------------- | |
264 | ||
265 | When cloning or pulling a repository containing submodules the submodules | |
266 | will not be checked out by default; You can instruct 'clone' to recurse | |
267 | into submodules. The 'init' and 'update' subcommands of 'git submodule' | |
268 | will maintain submodules checked out and at an appropriate revision in | |
269 | your working tree. Alternatively you can set 'submodule.recurse' to have | |
270 | 'checkout' recursing into submodules. | |
271 | ||
272 | ||
273 | SEE ALSO | |
274 | -------- | |
275 | linkgit:git-submodule[1], linkgit:gitmodules[5]. | |
276 | ||
277 | GIT | |
278 | --- | |
279 | Part of the linkgit:git[1] suite |