NAME | SYNOPSIS | DESCRIPTION | THE CONFIGURATION OF SUBMODULES | FORMS | WORKFLOW FOR A THIRD PARTY LIBRARY | WORKFLOW FOR AN ARTIFICIALLY SPLIT REPO | IMPLEMENTATION DETAILS | SEE ALSO | GIT | COLOPHON

GITSUBMODULES(7)                 Git Manual                 GITSUBMODULES(7)

NAME         top

       gitsubmodules - mounting one repository inside another

SYNOPSIS         top

       .gitmodules, $GIT_DIR/config

       git submodule
       git <command> --recurse-submodules

DESCRIPTION         top

       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.

THE CONFIGURATION OF SUBMODULES         top

       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.

FORMS         top

       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>/.

WORKFLOW FOR A THIRD PARTY LIBRARY         top

           # 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         top

           # 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         top

       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.

SEE ALSO         top

       git-submodule(1), gitmodules(5).

GIT         top

       Part of the git(1) suite

COLOPHON         top

       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
       2017-11-25.  (At that time, the date of the most recent commit that
       was found in the repository was 2017-11-21.)  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
       man-pages@man7.org

Git 2.14.0.rc1.14.gc             08/02/2017                 GITSUBMODULES(7)

Pages that refer to this page: git-rm(1)git-submodule(1)