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RRZ
Regional Computer
Center (RRZ)

Photo: Thomas Orgis

X11 Forwarding

X11 forwarding is needed to start an X Window (X11) graphical user interface on a remote computer.

Note that X11 forwarding has security implications and therefore should only be enabled when necessary (see man ssh). The ssh command line option for enabling X11 forwarding is -X.

The login gateways of Hummel-2 have no X11 software installed. To enable X11 forwarding the login gateway must be used as a jump host to a front-end node by using the -J option, e.g.:

$ ssh -X -J bxy1234@hummel3.rrz.uni-hamburg.de bxy1234@front1

In many cases jump hosts will only work if they are configured in the SSH client configuration file. A useful configuration for Hummel-2 can be found on the Jump Hosts page. With that configuration using the -X option is straightforward:

$ ssh -X hummel2-front1
$ ssh -X hummel2-front2

To test X11 functionality on a front-end node there is

  • the xlogo command which shows the X11 logo on your desktop,
  • the xeyes command – the follow the mouse demo.

Commands for testing X11 on a front-end node:

bxy1234@hummel2-front1:~$ module load xlogo
bxy1234@hummel2-front1:~$ xlogo
bxy1234@hummel2-front1:~$ module load xeyes
bxy1234@hummel2-front1:~$ xeyes