"X11 forwarding request failed on channel 3" [solved]

[TheCotMan]

I tried some searches with bing and google for an answer, but both failed.

This is a thread specific to this error and a solution.

user@source.example.com $ ssh -X user@target.example.com
X11 forwarding request failed on channel 3
user@target.example.com $

Turns out "xauth" package was missing on the target server target.example.com .

How this was found? Debug in ssh:

user@source.example.com $ ssh -v -X user@target.example.com
.
.
.
.
debug1: Requesting X11 forwarding with authentication spoofing.
debug1: Remote: No xauth program; cannot forward with spoofing.
X11 forwarding request failed on channel 3
user@target.example.com $

Add the xauth package, problem solved. (This thread is for search engines.)

I doubt many other people will encounter this problem.
Other channel failure errors can be found with the help of search engines.