Clone private git repo with dockerfile

I have copied this code from what seems to be various working dockerfiles around, here is mine: FROM ubuntu MAINTAINER Luke Crooks "luke@pumalo.org" # Update aptitude with new repo RUN apt-get update # Install software RUN apt-get install -y git python-virtualenv # Make ssh dir RUN mkdir /root/.ssh/ # Copy over private key, and set permissions ADD id_rsa /root/.ssh/id_rsa RUN chmod 700 /root/.ssh/