Why is the `git subtree` not working even though I have git 1.8.3.2 installed on Ubuntu 12.10?

It actually is installed on Ubuntu but for some reason it's not put anyplace where git can find it. Easiest way is to create a symlink:

sudo chmod +x /usr/share/doc/git/contrib/subtree/git-subtree.sh
sudo ln -s /usr/share/doc/git/contrib/subtree/git-subtree.sh /usr/lib/git-core/git-subtree

UPDATE 1: looks like a patch has been submitted upstream to fix this but it hasn't yet been merged.

UPDATE 2: the patch to fix this in Debian has been merged, but since they went the route of a separate git-subtree package I don't think this will make it to Ubuntu 12.04. Seems to not be an issue in 14.04 as /usr/lib/git-core/git-subtree is already created correctly by the git package.

It doesn't seem to be installed by the default package. This site has some directions: http://engineeredweb.com/blog/how-to-install-git-subtree

On Fedora, it is available as a separate package:

dnf install git-subtree