No xauth data; using fake authentication. Unable to display remote windows

Question

Whenever I try to ssh -X or -Y into a remote Linux server from my Mac (OSX Mavericks) machine, I get the same message:

"Warning: No xauth data; using fake authentication data for X11 forwarding."

I have tried several ideas that I found on SO threads, e.g. adding the following

Host *
ForwardX11 yes
ForwardX11Trusted yes

in my .ssh/config file (which is equivalent to always doing ssh -Y), deleting the .Xauthority file in the server, etc.

Why does this happen?

Most importantly, when I try to open a remote window (e.g. using ssh -Y, and then opening a plot in Python), I get the following message:

Could not find ':' in DISPLAY: xxx.yyy.net
: Fatal IO error: client killed

Solution

I should have known better, but OS X does not come with an X server. You need to install your own. Once you install XQuartz, you can restart and the problem goes away.