SSH X11 Forwarding

SSH supports tunneling of X11 (X-Windows). If you have an X11 server running on your local machine, you may use X11 applications on remote systems and have their graphical displays appear on your local machine. These X11 connections are tunneled and encrypted automatically by your SSH client.

Link to section 'Installing an X11 Server' of 'SSH X11 Forwarding' Installing an X11 Server

To use X11, you will need to have a local X11 server running on your personal machine. Both free and commercial X11 servers are available for various operating systems.

Linux / Solaris / AIX / HP-UX / Unix:

An X11 server is at the core of all graphical sessions. If you are logged in to a graphical environment on these operating systems, you are already running an X11 server.
ThinLinc is an alternative to running an X11 server directly on your Linux computer. ThinLinc is a service that allows you to connect to a persistent remote graphical desktop session.

Microsoft Windows:

ThinLinc is an alternative to running an X11 server directly on your Windows computer. ThinLinc is a service that allows you to connect to a persistent remote graphical desktop session.
MobaXterm is a small, easy to use, full-featured SSH client. It includes X11 support for remote displays, SFTP capabilities, and limited SSH authentication forwarding for keys.

Mac OS X:

X11 is available as an optional install on the Mac OS X install disks prior to 10.7/Lion. Run the installer, select the X11 option, and follow the instructions. For 10.7+ please download XQuartz.
ThinLinc is an alternative to running an X11 server directly on your Mac computer. ThinLinc is a service that allows you to connect to a persistent remote graphical desktop session.

Link to section 'Enabling X11 Forwarding in your SSH Client' of 'SSH X11 Forwarding' Enabling X11 Forwarding in your SSH Client

Once you are running an X11 server, you will need to enable X11 forwarding/tunneling in your SSH client:

ssh: X11 tunneling should be enabled by default. To be certain it is enabled, you may use ssh -Y.
MobaXterm: Select "New session" and "SSH." Under "Advanced SSH Settings" check the box for X11 Forwarding.

SSH will set the remote environment variable $DISPLAY to "localhost:XX.YY" when this is working correctly. If you had previously set your $DISPLAY environment variable to your local IP or hostname, you must remove any set/export/setenv of this variable from your login scripts. The environment variable $DISPLAY must be left as SSH sets it, which is to a random local port address. Setting $DISPLAY to an IP or hostname will not work.