GITSUBMODULES(7) Git Manual GITSUBMODULES(7)
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 Gits porcelain layer such as where to obtain the submodule
via the submodule.foo.url setting.
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 Gits 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. However you
can also use submodules to e.g. hold large binary assets and
these repositories are then 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.
· 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 submodule
specs. Most commands have a boolean flag --recurse-submodules
whether to recurse into submodules. Examples are ls-files or
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, which does
pay attention to its .gitignore file.
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.
Typical configuration at this place is controlling if a submodule
is recursed into at all via the active flag for example.
If the submodule is not yet initialized, then the configuration
inside the submodule does not exist yet, so configuration where
to obtain the submodule from is configured here for example.
· the .gitmodules file inside the superproject. Additionally to the
required mapping between submodule’s name and path, a project
usually uses this file to suggest defaults for the upstream
collection of repositories.
This file mainly serves as the mapping between name and path 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.
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>/.
# 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:
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.
git-submodule(1), gitmodules(5).
Part of the git(1) suite
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Git 2.14.0.rc1.14.gc 08/02/2017 GITSUBMODULES(7)
Pages that refer to this page: git-rm(1), git-submodule(1)
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