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   local$> echo $DISPLAY
   local$> ssh -X -i PEMFILE ec2-user@AMAZONEC2_AMI
   [ec2-user@REMOTE_AMI ~]$ echo $DISPLAY

   [ec2-user@REMOTE_AMI ~]$ sudo grep X11 /etc/ssh/sshd_config ~/.ssh/*
   /etc/ssh/sshd_config:#X11Forwarding no
   /etc/ssh/sshd_config:X11Forwarding yes
   /etc/ssh/sshd_config:#X11DisplayOffset 10
   /etc/ssh/sshd_config:#X11UseLocalhost yes

Hence the display is not forwarded. a command like emacs & for instance does not show the X11 window on the local desktop. Please advise.

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Did you restart your sshd after changing X11Forwarding to yes? – Olli Feb 22 '11 at 19:52
You can also check to see if there is any interesting warning/notes when you run ssh -vvvv -X -i ... – Alex Feb 22 '11 at 19:53
X11Forwading was set to yes from before. For -vvvv debug1: Remote: No xauth program; cannot forward with spoofing. Could this be the reason ? – Humble Debugger Feb 23 '11 at 15:51
up vote 18 down vote accepted

I did this:

sudo yum install xorg-x11-xauth.x86_64 xorg-x11-server-utils.x86_64 dbus-x11.x86_64

and I finally got a display variable and it all started to work!

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this also worked for me. – xaxxon Dec 30 '11 at 1:42
worked for me - I ran the command exactly as presented, then I logged out, and logged back in using ssh -XY – Escualo Feb 24 '12 at 18:07
I had to reboot my instance in order to get sshd to start offering me X11 forwarding: simply restarting sshd wasn't enough. – crb Feb 27 '12 at 13:48
Worked for me on 6.2, no restarting needed. – aaa90210 Jun 6 '14 at 7:52

Install from the above answer didn't work for my RHEL 6.2 EC2 instance. Here are steps that did work:

$ sudo yum groupinstall "X Window System"

# now disconnect and create a new SSH with -X option

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