NAME
gitsubmodules - Mounting one repository inside anotherSYNOPSIS
.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. 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
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
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
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.
[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
[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
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
# 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) suite02/28/2023 | Git 2.39.2 |