Given: an Ubuntu server with central Git repository and connection via SSH and an Ubuntu client with local Git repository.
- Deposit user’s SSH private key 
id_rsain~/.ssh(aka/home/user/.ssh) chmod 0600 ~/.ssh/id_rsato prevent other users reading user’s private key- If you also want to use Git with root user: 
cp /home/user/.ssh/id_rsa /root/.ssh/ - Connect with 
git clone user@server:/path/to/git/<centralrepo>/ <localrepo>