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 the 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
# 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 2.27.0 06/01/2020 GITSUBMODULES(7)