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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 | |
39 | hints to Gits porcelain layer such as where to obtain the submodule via | |
40 | the `submodule.foo.url` setting. | |
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 | |
54 | overcome current limitations of Gits implementation to have | |
55 | finer grained access: | |
56 | ||
57 | * Size of the git repository: | |
58 | In its current form Git scales up poorly for large repositories containing | |
59 | content that is not compressed by delta computation between trees. | |
60 | However you can also use submodules to e.g. hold large binary assets | |
61 | and these repositories are then shallowly cloned such that you do not | |
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. | |
66 | * Access control: | |
67 | By restricting user access to submodules, this can be used to implement | |
68 | read/write policies for different users. | |
69 | ||
70 | The configuration of submodules | |
71 | ------------------------------- | |
72 | ||
73 | Submodule operations can be configured using the following mechanisms | |
74 | (from highest to lowest precedence): | |
75 | ||
76 | * The command line for those commands that support taking submodule specs. | |
77 | Most commands have a boolean flag '--recurse-submodules' whether to | |
78 | recurse into submodules. Examples are `ls-files` or `checkout`. | |
79 | Some commands take enums, such as `fetch` and `push`, where you can | |
80 | specify how submodules are affected. | |
81 | ||
82 | * The configuration inside the submodule. This includes `$GIT_DIR/config` | |
83 | in the submodule, but also settings in the tree such as a `.gitattributes` | |
84 | or `.gitignore` files that specify behavior of commands inside the | |
85 | submodule. | |
86 | + | |
87 | For example an effect from the submodule's `.gitignore` file | |
88 | would be observed when you run `git status --ignore-submodules=none` in | |
89 | the superproject. This collects information from the submodule's working | |
90 | directory by running `status` in the submodule, which does pay attention | |
91 | to its `.gitignore` file. | |
92 | + | |
93 | The submodule's `$GIT_DIR/config` file would come into play when running | |
94 | `git push --recurse-submodules=check` in the superproject, as this would | |
95 | check if the submodule has any changes not published to any remote. The | |
96 | remotes are configured in the submodule as usual in the `$GIT_DIR/config` | |
97 | file. | |
98 | ||
99 | * The configuration file `$GIT_DIR/config` in the superproject. | |
100 | Typical configuration at this place is controlling if a submodule | |
101 | is recursed into at all via the `active` flag for example. | |
102 | + | |
103 | If the submodule is not yet initialized, then the configuration | |
104 | inside the submodule does not exist yet, so configuration where to | |
105 | obtain the submodule from is configured here for example. | |
106 | ||
107 | * the `.gitmodules` file inside the superproject. Additionally to the | |
108 | required mapping between submodule's name and path, a project usually | |
109 | uses this file to suggest defaults for the upstream collection | |
110 | of repositories. | |
111 | + | |
112 | This file mainly serves as the mapping between name and path in | |
113 | the superproject, such that the submodule's git directory can be | |
114 | located. | |
115 | + | |
116 | If the submodule has never been initialized, this is the only place | |
117 | where submodule configuration is found. It serves as the last fallback | |
118 | to specify where to obtain the submodule from. | |
119 | ||
120 | FORMS | |
121 | ----- | |
122 | ||
123 | Submodules can take the following forms: | |
124 | ||
125 | * The basic form described in DESCRIPTION with a Git directory, | |
126 | a working directory, a `gitlink`, and a `.gitmodules` entry. | |
127 | ||
128 | * "Old-form" submodule: A working directory with an embedded | |
129 | `.git` directory, and the tracking `gitlink` and `.gitmodules` entry in | |
130 | the superproject. This is typically found in repositories generated | |
131 | using older versions of Git. | |
132 | + | |
133 | It is possible to construct these old form repositories manually. | |
134 | + | |
135 | When deinitialized or deleted (see below), the submodule’s Git | |
136 | directory is automatically moved to `$GIT_DIR/modules/<name>/` | |
137 | of the superproject. | |
138 | ||
139 | * Deinitialized submodule: A `gitlink`, and a `.gitmodules` entry, | |
140 | but no submodule working directory. The submodule’s git directory | |
141 | may be there as after deinitializing the git directory is kept around. | |
142 | The directory which is supposed to be the working directory is empty instead. | |
143 | + | |
144 | A submodule can be deinitialized by running `git submodule deinit`. | |
145 | Besides emptying the working directory, this command only modifies | |
146 | the superproject’s `$GIT_DIR/config` file, so the superproject’s history | |
147 | is not affected. This can be undone using `git submodule init`. | |
148 | ||
149 | * Deleted submodule: A submodule can be deleted by running | |
150 | `git rm <submodule path> && git commit`. This can be undone | |
151 | using `git revert`. | |
152 | + | |
153 | The deletion removes the superproject’s tracking data, which are | |
154 | both the `gitlink` entry and the section in the `.gitmodules` file. | |
155 | The submodule’s working directory is removed from the file | |
156 | system, but the Git directory is kept around as it to make it | |
157 | possible to checkout past commits without requiring fetching | |
158 | from another repository. | |
159 | + | |
160 | To completely remove a submodule, manually delete | |
161 | `$GIT_DIR/modules/<name>/`. | |
162 | ||
163 | Workflow for a third party library | |
164 | ---------------------------------- | |
165 | ||
166 | # add a submodule | |
167 | git submodule add <url> <path> | |
168 | ||
169 | # occasionally update the submodule to a new version: | |
170 | git -C <path> checkout <new version> | |
171 | git add <path> | |
172 | git commit -m "update submodule to new version" | |
173 | ||
174 | # See the list of submodules in a superproject | |
175 | git submodule status | |
176 | ||
177 | # See FORMS on removing submodules | |
178 | ||
179 | ||
180 | Workflow for an artificially split repo | |
181 | -------------------------------------- | |
182 | ||
183 | # Enable recursion for relevant commands, such that | |
184 | # regular commands recurse into submodules by default | |
185 | git config --global submodule.recurse true | |
186 | ||
187 | # Unlike the other commands below clone still needs | |
188 | # its own recurse flag: | |
189 | git clone --recurse <URL> <directory> | |
190 | cd <directory> | |
191 | ||
192 | # Get to know the code: | |
193 | git grep foo | |
194 | git ls-files | |
195 | ||
196 | # Get new code | |
197 | git fetch | |
198 | git pull --rebase | |
199 | ||
200 | # change worktree | |
201 | git checkout | |
202 | git reset | |
203 | ||
204 | Implementation details | |
205 | ---------------------- | |
206 | ||
207 | When cloning or pulling a repository containing submodules the submodules | |
208 | will not be checked out by default; You can instruct 'clone' to recurse | |
209 | into submodules. The 'init' and 'update' subcommands of 'git submodule' | |
210 | will maintain submodules checked out and at an appropriate revision in | |
211 | your working tree. Alternatively you can set 'submodule.recurse' to have | |
212 | 'checkout' recursing into submodules. | |
213 | ||
214 | ||
215 | SEE ALSO | |
216 | -------- | |
217 | linkgit:git-submodule[1], linkgit:gitmodules[5]. | |
218 | ||
219 | GIT | |
220 | --- | |
221 | Part of the linkgit:git[1] suite |