git submodule update — initialize and update all submodules

Quick Answer

# Initialize and update all submodules (run after git clone)
git submodule update --init --recursive

When to use this

You cloned a repository that uses submodules and the submodule directories are empty, or a teammate added a new submodule and your local copy is out of date.

Other causes & fixes

Clone a repo and initialize submodules in one command

git clone --recurse-submodules https://github.com/user/repo.git

Pull latest changes in all submodules

git submodule update --remote --recursive

Show submodule status

git submodule status