GITSUBMODULES(7)		  Git Manual		      GITSUBMODULES(7)



NAME
       gitsubmodules - Mounting one repository inside another

SYNOPSIS
       .gitmodules, $GIT_DIR/config

       git submodule
       git <command> --recurse-submodules


DESCRIPTION
       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:

	   o   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.

	   o   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.

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

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

       o   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.

       o   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.

       o   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.

       o   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
       Submodules can take the following forms:

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

       o   "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.

       o   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.

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

GIT
       Part of the git(1) suite



Git 2.38.4			  02/20/2023		      GITSUBMODULES(7)