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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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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 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:
• 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 specifies 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.
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>/.
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 submodules 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.
# 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 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
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 recurse 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
This page is part of the git (Git distributed version control
system) project. Information about the project can be found at
⟨http://git-scm.com/⟩. If you have a bug report for this manual
page, see ⟨http://git-scm.com/community⟩. This page was obtained
from the project's upstream Git repository
⟨https://github.com/git/git.git⟩ on 2024-06-14. (At that time,
the date of the most recent commit that was found in the
repository was 2024-06-12.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
Git 2.45.2.492.gd63586 2024-06-12 GITSUBMODULES(7)
Pages that refer to this page: git(1), git-config(1), git-fetch(1), git-rm(1), git-submodule(1), gitmodules(5)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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