You may have realised that when you try use ssh -Y on another Mac from Mountain Lion you get the following error : Warning: No xauth data; using fake authentication data for X11 forwarding.X11 forwarding request failed on channel 0 Fixing this error only takes some simple configuration. All you have to do is add these lines to the following files on both machines: /etc/sshd_config X11Forwarding yes XauthLocation /opt/X11/bin/xauth XauthLocation /usr/X11R6/bin/xauth /etc/ssh_config XauthLocation /opt/X11/bin/xauth XauthLocation /usr/X11R6/bin/xauth That should be all you need to get rid of the authentication error. Hope this was helpful.