Update Git submodule to latest commit on origin

gistfile1.txt

# 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"

Credit to: 

http://stackoverflow.com/questions/5828324/update-git-submodule-to-latest-commit-on-origin