First, you should rule out any server-side problems. Are you able to ssh -X from any other host successfully? Does ssh -Y work while ssh -X doesn’t? In either case, assume ssh + X11 is set up correctly on your server and move on to the next section.

If you aren’t in a position to check that (you have but your one laptop running X11, say), you can ssh from the server to itself using a fake session:

  1. export DISPLAY=:44 # (Bourne shell) or
    setenv DISPLAY :44 # (csh / tcsh)
  2. xauth add $DISPLAY MIT-MAGIC-COOKIE-1 1234 # Bogus cookie just for this test
  3. ssh -X localhost env |grep DISPLAY

Expected result: there should be a DISPLAY variable set on the remote end of the ssh-to-self session. If you get no result, your server is likely mis-configured (e.g. the X11 libraries and/or the xauth command could be missing; or the sshd configuration could be set to deny X11 access)

As per Will Angley’s answer

The error message you cite is a symptom that can have many causes. Try again with ssh -X -vv remotehost, which should give you additional clues as to why the X11 tunnel setup failed.

Do you see the following message appearing?

debug1: No xauth program.

If so,

  1. Take note of where on your client system, the xauth command resides:
    which xauth
  2. Add the following at the very end of your ~/.ssh/config (and add a comment to remind yourself to keep it there in the future):
    Host *
        XAuthLocation /opt/X11/bin/xauth
    

    Adjust this path as per findings of step 1 — Credits to Jan-Willem Arnold

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