Update Git submodule to latest commit on origin

The git submodule update command actually tells Git that you want your submodules to each check out the commit already specified in the index of the superproject. If you want to update your submodules to the latest commit available from their remote, you will need to do this directly in the submodules.

So in summary:

# Get the submodule initially
git submodule add ssh://bla submodule_dir
git submodule init

# Time passes, submodule upstream is updated
# and you now want to update

# Change to the submodule directory
cd submodule_dir

# Checkout desired branch
git checkout master

# Update
git pull

# Get back to your project root
cd ..

# Now the submodules are in the state you want, so
git commit -am "Pulled down update to submodule_dir"

Or, if you're a busy person:

git submodule foreach git pull origin master

Git 1.8.2 features a new option, --remote, that will enable exactly this behavior. Running

git submodule update --remote --merge

will fetch the latest changes from upstream in each submodule, merge them in, and check out the latest revision of the submodule. As the documentation puts it:

--remote

This option is only valid for the update command. Instead of using the superproject’s recorded SHA-1 to update the submodule, use the status of the submodule’s remote-tracking branch.

This is equivalent to running git pull in each submodule, which is generally exactly what you want.

In your project parent directory, run:

git submodule update --init

Or if you have recursive submodules run:

git submodule update --init --recursive

Sometimes this still doesn't work, because somehow you have local changes in the local submodule directory while the submodule is being updated.

Most of the time the local change might not be the one you want to commit. It can happen due to a file deletion in your submodule, etc. If so, do a reset in your local submodule directory and in your project parent directory, run again:

git submodule update --init --recursive