With git submodule update I don’t see an option to specify branch. What happens is, it will fetch either all branches or one (if --single-branch is specified), which is default, but not the custom.

With very big repositories, it is problematic, because I have to fetch wrong branches and then it will checkout from another “reference”, not much related with default branch, making it much longer to update submodule and also taking more space (as it will fetch unnecessary branch).

Even if I have .gitmodules with branch specified, it is ignored. For example

let say default branch is master and I have this in .gitmodules:

[submodule "my/path/to/sub"]
    path = my/path/to/sub
    url = [email protected]:org/sub.git
    branch = 16.0

I would expect when doing git submodule update --init --single-branch, to fetch 16.0 branch, but what it does, it will fetch master branch and will then checkout to commit that is referenced by superproject.