Update a bare repository

Hello, what I would like to do is the following:

I have a _bare_ clone of a git repository and would like to update it from Junios repository at kernel.org from time to time.

How do I do that? In a way that it is a fire and forget solution? It should also fetch new upstream branches.

"git pull" does not work. "git fetch" does, but it does update all references?

	(faui02) [~/work/repositories/mirror/git.git] git pull
	fatal: /usr/bin/git-pull cannot be used without a working tree.
	(faui02) [~/work/repositories/mirror/git.git] git fetch
	(faui02) [~/work/repositories/mirror/git.git]

I also would like to check that it is impossible to push anything to the repository.

		Thomas