Graphical programs (X11)

Some programs on a Linux server have windows of their own: virt-manager, Wireshark, an installer, xclock. With X11 turned on for a host, a program you start in its terminal opens its window on your Mac, as ssh -Y does.

On your Mac, once

Install XQuartz, the free X11 server for the Mac, from xquartz.org.
Log out of your Mac and in again. Until then, programs cannot find XQuartz. The host editor says which of the two is still to do.

For a host

Edit the host (in its menu, Edit…) and tick Open their windows on this Mac (X11) under Graphical programs.
Open a new tab to it and start the program, for example xclock &. XQuartz starts by itself and the window opens beside Wayfinder.

This is for hosts made in Wayfinder. For a host in your own ~/.ssh/config, add ForwardX11 yes and ForwardX11Trusted yes to its block, or choose Duplicate as a Wayfinder Host… in its menu and tick it on the copy.

On the server

Its SSH server must allow it: X11Forwarding yes in /etc/ssh/sshd_config, and the xauth program installed (the package is called xauth or xorg-x11-xauth). After a change, reload sshd. In the terminal, echo $DISPLAY then shows something like localhost:10.0.

Good to know

Forwarding is trusted, as ssh -Y is: untrusted forwarding ends after twenty minutes and many programs fail under it. Turn it on only for servers you trust, since a program there can read what XQuartz shows.
Every tab to the host shares one connection, so a program started in any of them can open windows.
Windows are drawn over the network. Over a slow link, a program with a lot to draw is slow too.