gitsubmodules(7) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | THE CONFIGURATION OF SUBMODULES | FORMS | ACTIVE SUBMODULES | WORKFLOW FOR A THIRD PARTY LIBRARY | WORKFLOW FOR AN ARTIFICIALLY SPLIT REPO | IMPLEMENTATION DETAILS | SEE ALSO | GIT | COLOPHON

GITSUBMODULES(7)               Git Manual               GITSUBMODULES(7)

NAME         top

       gitsubmodules - Mounting one repository inside another

SYNOPSIS         top

       .gitmodules, $GIT_DIR/config

       git submodule
       git <command> --recurse-submodules

DESCRIPTION         top

       A submodule is a repository embedded inside another repository.
       The submodule has its own history; the repository it is embedded
       in is called a superproject.

       On the filesystem, a submodule usually (but not always - see
       FORMS below) consists of (i) a Git directory located under the
       $GIT_DIR/modules/ directory of its superproject, (ii) a working
       directory inside the superproject’s working directory, and a .git
       file at the root of the submodule’s working directory pointing to
       (i).

       Assuming the submodule has a Git directory at
       $GIT_DIR/modules/foo/ and a working directory at path/to/bar/,
       the superproject tracks the submodule via a gitlink entry in the
       tree at path/to/bar and an entry in its .gitmodules file (see
       gitmodules(5)) of the form submodule.foo.path = path/to/bar.

       The gitlink entry contains the object name of the commit that the
       superproject expects the submodule’s working directory to be at.

       The section submodule.foo.* in the .gitmodules file gives
       additional hints to Git’s porcelain layer. For example, the
       submodule.foo.url setting specifies where to obtain the
       submodule.

       Submodules can be used for at least two different use cases:

        1. Using another project while maintaining independent history.
           Submodules allow you to contain the working tree of another
           project within your own working tree while keeping the
           history of both projects separate. Also, since submodules are
           fixed to an arbitrary version, the other project can be
           independently developed without affecting the superproject,
           allowing the superproject project to fix itself to new
           versions only when desired.

        2. Splitting a (logically single) project into multiple
           repositories and tying them back together. This can be used
           to overcome current limitations of Git’s implementation to
           have finer grained access:

           •   Size of the Git repository: In its current form Git
               scales up poorly for large repositories containing
               content that is not compressed by delta computation
               between trees. For example, you can use submodules to
               hold large binary assets and these repositories can be
               shallowly cloned such that you do not have a large
               history locally.

           •   Transfer size: In its current form Git requires the whole
               working tree present. It does not allow partial trees to
               be transferred in fetch or clone. If the project you work
               on consists of multiple repositories tied together as
               submodules in a superproject, you can avoid fetching the
               working trees of the repositories you are not interested
               in.

           •   Access control: By restricting user access to submodules,
               this can be used to implement read/write policies for
               different users.

THE CONFIGURATION OF SUBMODULES         top

       Submodule operations can be configured using the following
       mechanisms (from highest to lowest precedence):

       •   The command line for those commands that support taking
           submodules as part of their pathspecs. Most commands have a
           boolean flag --recurse-submodules which specify whether to
           recurse into submodules. Examples are grep and checkout. Some
           commands take enums, such as fetch and push, where you can
           specify how submodules are affected.

       •   The configuration inside the submodule. This includes
           $GIT_DIR/config in the submodule, but also settings in the
           tree such as a .gitattributes or .gitignore files that
           specify behavior of commands inside the submodule.

           For example an effect from the submodule’s .gitignore file
           would be observed when you run git status
           --ignore-submodules=none in the superproject. This collects
           information from the submodule’s working directory by running
           status in the submodule while paying attention to the
           .gitignore file of the submodule.

           The submodule’s $GIT_DIR/config file would come into play
           when running git push --recurse-submodules=check in the
           superproject, as this would check if the submodule has any
           changes not published to any remote. The remotes are
           configured in the submodule as usual in the $GIT_DIR/config
           file.

       •   The configuration file $GIT_DIR/config in the superproject.
           Git only recurses into active submodules (see "ACTIVE
           SUBMODULES" section below).

           If the submodule is not yet initialized, then the
           configuration inside the submodule does not exist yet, so
           where to obtain the submodule from is configured here for
           example.

       •   The .gitmodules file inside the superproject. A project
           usually uses this file to suggest defaults for the upstream
           collection of repositories for the mapping that is required
           between a submodule’s name and its path.

           This file mainly serves as the mapping between the name and
           path of submodules in the superproject, such that the
           submodule’s Git directory can be located.

           If the submodule has never been initialized, this is the only
           place where submodule configuration is found. It serves as
           the last fallback to specify where to obtain the submodule
           from.

FORMS         top

       Submodules can take the following forms:

       •   The basic form described in DESCRIPTION with a Git directory,
           a working directory, a gitlink, and a .gitmodules entry.

       •   "Old-form" submodule: A working directory with an embedded
           .git directory, and the tracking gitlink and .gitmodules
           entry in the superproject. This is typically found in
           repositories generated using older versions of Git.

           It is possible to construct these old form repositories
           manually.

           When deinitialized or deleted (see below), the submodule’s
           Git directory is automatically moved to
           $GIT_DIR/modules/<name>/ of the superproject.

       •   Deinitialized submodule: A gitlink, and a .gitmodules entry,
           but no submodule working directory. The submodule’s Git
           directory may be there as after deinitializing the Git
           directory is kept around. The directory which is supposed to
           be the working directory is empty instead.

           A submodule can be deinitialized by running git submodule
           deinit. Besides emptying the working directory, this command
           only modifies the superproject’s $GIT_DIR/config file, so the
           superproject’s history is not affected. This can be undone
           using git submodule init.

       •   Deleted submodule: A submodule can be deleted by running git
           rm <submodule path> && git commit. This can be undone using
           git revert.

           The deletion removes the superproject’s tracking data, which
           are both the gitlink entry and the section in the .gitmodules
           file. The submodule’s working directory is removed from the
           file system, but the Git directory is kept around as it to
           make it possible to checkout past commits without requiring
           fetching from another repository.

           To completely remove a submodule, manually delete
           $GIT_DIR/modules/<name>/.

ACTIVE SUBMODULES         top

       A submodule is considered active,

        1. if submodule.<name>.active is set to true

           or

        2. if the submodule’s path matches the pathspec in
           submodule.active

           or

        3. if submodule.<name>.url is set.

       and these are evaluated in this order.

       For example:

           [submodule "foo"]
             active = false
             url = https://example.org/foo
           [submodule "bar"]
             active = true
             url = https://example.org/bar
           [submodule "baz"]
             url = https://example.org/baz

       In the above config only the submodule bar and baz are active,
       bar due to (1) and baz due to (3). foo is inactive because (1)
       takes precedence over (3)

       Note that (3) is a historical artefact and will be ignored if the
       (1) and (2) specify that the submodule is not active. In other
       words, if we have a submodule.<name>.active set to false or if
       the submodule’s path is excluded in the pathspec in
       submodule.active, the url doesn’t matter whether it is present or
       not. This is illustrated in the example that follows.

           [submodule "foo"]
             active = true
             url = https://example.org/foo
           [submodule "bar"]
             url = https://example.org/bar
           [submodule "baz"]
             url = https://example.org/baz
           [submodule "bob"]
             ignore = true
           [submodule]
             active = b*
             active = :(exclude) baz

       In here all submodules except baz (foo, bar, bob) are active. foo
       due to its own active flag and all the others due to the
       submodule active pathspec, which specifies that any submodule
       starting with b except baz are also active, regardless of the
       presence of the .url field.

WORKFLOW FOR A THIRD PARTY LIBRARY         top

           # Add a submodule
           git submodule add <url> <path>

           # Occasionally update the submodule to a new version:
           git -C <path> checkout <new version>
           git add <path>
           git commit -m "update submodule to new version"

           # See the list of submodules in a superproject
           git submodule status

           # See FORMS on removing submodules

WORKFLOW FOR AN ARTIFICIALLY SPLIT REPO         top

           # Enable recursion for relevant commands, such that
           # regular commands recurse into submodules by default
           git config --global submodule.recurse true

           # Unlike most other commands below, clone still needs
           # its own recurse flag:
           git clone --recurse <URL> <directory>
           cd <directory>

           # Get to know the code:
           git grep foo
           git ls-files --recurse-submodules

           Note
           git ls-files also requires its own --recurse-submodules flag.

           # Get new code
           git fetch
           git pull --rebase

           # Change worktree
           git checkout
           git reset

IMPLEMENTATION DETAILS         top

       When cloning or pulling a repository containing submodules the
       submodules will not be checked out by default; you can instruct
       clone to recurse into submodules. The init and update subcommands
       of git submodule will maintain submodules checked out and at an
       appropriate revision in your working tree. Alternatively you can
       set submodule.recurse to have checkout recursing into submodules
       (note that submodule.recurse also affects other Git commands, see
       git-config(1) for a complete list).

SEE ALSO         top

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

GIT         top

       Part of the git(1) suite

COLOPHON         top

       This page is part of the git (Git distributed version control
       system) project.  Information about the project can be found at
       ⟨http://git-scm.com/⟩.  If you have a bug report for this manual
       page, see ⟨http://git-scm.com/community⟩.  This page was obtained
       from the project's upstream Git repository
       ⟨https://github.com/git/git.git⟩ on 2021-08-27.  (At that time,
       the date of the most recent commit that was found in the
       repository was 2021-08-24.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

Git 2.33.0.69.gc420321         08/27/2021               GITSUBMODULES(7)

Pages that refer to this page: git(1)git-config(1)git-rm(1)git-submodule(1)gitmodules(5)