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X11 is a legacy UNIX/Linux display technology


The X11 protocol has been used for graphical programs on UNIX platforms for decades but is gradually being phased out. One unique feature is the ability to run graphical programs on a remote machine with the program windows being drawn by your location computer.

We strongly recommend the use of VNC (or web equivalents such as Open On Demand) where these are available, but you may occasionally need to run remote X11 applications - VNC is much less sensitive to the speed of your network and programs survive network interruptions.

Using X11

To access a graphical program from one of FMRIB's Linux servers you need a SSH client, used to encrypt the connection and allow you to type the commands that launch the program. To display the graphics you also need to install and run a X11 'server' on your local computer.


Installing and using X11 on macOS


To run X11 programs you need download and install XQuartz​.


Since XQuartz 2.7.9 the indirect GLX mode is disabled by default. This prevents you from running FSLeyes over an SSH connection (although we strongly recommend you use VNC for this purpose).

To re-enable this, open a terminal and use the following commands:

Version 2.8+:

defaults write org.xquartz.X11 enable_iglx -bool true​

Version 2.7.x:

defaults write org.macosforge.xquartz.X11 enable_iglx -bool true

Now restart XQuartz (if it is running).

You may have to repeat this after Xquartz updates.


To launch a remote X11 application, use SSH with X11 tunnelling to connect to a remote Linux host and then run the graphical program.

Running remote X11 software on Linux

As X11 is still in active use for many graphical programs on Linux there is no need to install any software.

See X11 forwarding over SSH to connect and encrypt the X11 connection and then launch the required application.

Using MobaXterm for X11 software


Download and install MobaXterm from


See our SSH pages for details on X11 forwarding.