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.