# gitsubmodules

## 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:
    
               •   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 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.
    


## 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.
    
           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.
    


## 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** recurse into submodules
           (note that **submodule.recurse** also affects other Git commands, see
           git-config(1) for a complete list).
    


## GIT



           Part of the git(1) suite
    


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