A quick post as a reminder to my future self: if ssh does not want to forward X11 despite using -X or -Y options, it might be because I am missing Xauth installed:

~local# ssh -YC remote
X11 forwarding request failed on channel 0
Last login: Tue Apr 26 09:09:47 2016 from local
~remote# yum install xauth
~remote# logout
~local# ssh -YC remote
~remote#

I keep forgetting about it when I install some bare-bone machines...