I got the following error message when I use ssh -v -Y. The server OS is mojave. Does anybody know what is wrong?

debug1: No xauth program.
Warning: No xauth data; using fake authentication data for X11 forwarding.
debug1: Requesting X11 forwarding with authentication spoofing.
debug1: Sending environment.
debug1: Sending env LANG = en_US.UTF-8
debug1: Remote: No xauth program; cannot forward X11.
X11 forwarding request failed on channel 0
  • Do you have X11 installed on your MacOS system? – larsks Nov 17 '19 at 4:11
  • How to check it? I have this $ which xauth /opt/X11/bin/xauth – user1424739 Nov 17 '19 at 4:18
  • Is that on the server? – larsks Nov 17 '19 at 4:20
  • Yes. It is on the server. – user1424739 Nov 17 '19 at 4:21
  • In that case, I'm not sure why you're getting that error. I don't have a MacOS system on which I can check. Hopefully someone else will help out! – larsks Nov 17 '19 at 4:22

Add /opt/X11/bin to your PATH in ~/.bashrc, e.g.

case $PATH in
    (*"/opt/X11/bin"*) ;;
    (*) PATH=$PATH:/opt/X11/bin ;;

at the very start of the file.

(Strictly one ought to look for "/opt/X11/bin:"*|*":/opt/X11/bin:"*|*":/opt/X11/bin"|"/opt/X11/bin" but *"/opt/X11/bin"* is almost certainly good enough)

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Both your client and the server are complaining that they can't find the xauth program. The "debug1: No xauth program" message comes from your client, saying it can't find a copy of xauth locally. The "Remote: No xauth program; cannot forward X11" message is from the server, saying it can't find xauth either. The default location for both client and server is /usr/X11R6/bin/xauth, though your vendor could change it.

For the client, you can set the Xauth location in your .ssh/config:

XAuthLocation /some/path/to/xauth

For the server, you must set the location in the remote server's sshd_config:

XAuthLocation /opt/X11/bin/xauth

After modifying the config, you should run sshd -t to validate the config, then restart sshd to make it reread the file.

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