Update: As of Git 1.7.0, converting existing branches to tracking branches got a whole lot easier. git push now has a -u flag which will set up tracking based on a successful push.

$ git push -u hub master
Branch master set up to track remote branch master from hub.

For reference, here’s the original post:

There are two ways to convert an existing branch to a remote tracking branch, using git config or directly editing the .git/config file.

In both of these examples, the local and remote branches are named “master”. The remote repository is “hub”.

git config commands

$ git config branch.master.remote hub
$ git config branch.master.merge refs/heads/master

editing .git/config

All the git config commands do is add the following to .git/config, editing the file manually has the same result.

[branch "master"]
    remote = hub
    merge = refs/heads/master

What would be nice is an additional config command, branch.<name>.track, which would split a full refspec, sending the relevant parts to the remote and merge commands.