git-submodule

git submodule

Git submodules are implemented using two moving parts:

• the .gitmodules file
• and a special kind of tree object(with mode 160000)

Git submodules put specific repo(what) to a specific path(where) in the super project with the specific commit(when):

• what - url in .gitmodule files.
• where - path in .gitmodule files.
• when - a special file object in the super projects, which has the commit SHA1 of the submodules.

How to track a branch of a submodule?

-b <branch> option in git submodule add, will add branch in .gitmodule file, which affect the behavior of git submodule update --remote.