ECPS cluster : SSH and X11 configuration (Mac OS X)

In order to access the ECPS cluster via a shell interface, use the ssh command in a terminal (both installed by default on Mac OS X).

  1. Inquire about your GASPAR (EPFL-wide) login name and password (these would be the same as e.g. those that you use for the wi-fi)
    💡If you don't know or don't have GASPAR credentials, get in touch with the STI-IT help desk in room ELB132
  2. Ensure that Prof. Cevher has made you a member of group ECPS (that group should show up in your list of groups)
  3. Open the Terminal application on your Mac (for instance, invoke Spotlight by clicking the 🔍 at the top right of your screen, and type Terminal)
  4. Once the Terminal opens, type
    ssh -X
    (be sure to replace mygaspar with your GASPAR login name obtained at step 1)
  5. Type your password when prompted.
  6. We have now validated that your password is working and that you have access to ECPS. Close the terminal and open a new one; and follow the instructions to set up password-less authentication using a public key.
  7. ssh has a whole bunch of tips and tricks that could make your life easier: for instance you can create a .ssh/config file so that you can safely forget about the -X flag (the latter by setting ForwardX11 yes).

In order to launch graphical applications (such as Matlab), X11 is also required.

To run an X11 program:

  1. Access the ECPS front-end node as shown above. Be sure to employ ssh -X (or have ForwardX11 set in your .ssh/config)
  2. Run a test X11 program such as xterm or xeyes
  3. ssh again from there to one of the compute nodes, e.g.
    ssh ecpsc12
    💡Among cluster nodes, plain ssh works without further configuration (no -X,  login name, or password needed)
  4. Again, run a test X11 program


I get an annoying message about X11 authentication

If you get this message:
Warning: untrusted X11 forwarding setup failed: xauth key data not generated
then the recommended solution is to upgrade Xquartz to 2.7.8 (currently a release candidate version, but it works good enough for me - Dominique, 20150626)

After a couple of minutes of keeping my ssh connection open, I cannot run X11 clients anymore

You need to increase the value of ForwardX11Timeout in your .ssh/config , e.g. like this:

Host *
    ForwardX11 yes
    ForwardX11Timeout 596h

(see also: diagnosis)