gitsubmodules






gitsubmodules − Mounting one repository inside another



.gitmodules, $GIT_DIR/config

git submodule
git <command> −−recurse−submodules




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









                             ‐2‐


     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.



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









                             ‐3‐


     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.



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.










                             ‐4‐


     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>/.



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)










                             ‐5‐


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.



     # 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



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

     # Unlike the other commands below clone still needs
     # its own recurse flag:
     git clone −−recurse <URL> <directory>
     cd <directory>

     # Get to know the code:









                             ‐6‐


     git grep foo
     git ls−files

     # Get new code
     git fetch
     git pull −−rebase

     # change worktree
     git checkout
     git reset



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).



git‐submodule(1), gitmodules(5).



Part of the git(1) suite