Testing With Graphics

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If you need to use graphics while testing your code, e.g. when using a debugger such as DDT or DDD, you have the following options:

Use the debugjob command

  • You can use the debugjob command which automatically provides X-forwarding support.
    $ ssh  niagara.scinet.utoronto.ca -X
    USER@nia-login07:~$ debugjob
    debugjob: Requesting 1 nodes for 60 minutes
    xalloc: Granted job allocation 189857
    xalloc: Waiting for resource configuration
    xalloc: Nodes nia0030 are ready for job
    [USER@nia1265 ~]$

    Use the regular queue

  • If debugjob is not suitable for your case due to the limitations either on time or resources (see above #Testing), then you have to follow these steps: You will need two terminals in order to achieve this:
    1. In the 1st terminal
      • ssh to niagara.scinet.utoronto.ca and issue your salloc command
      • wait until your resources are allocated and you are assigned the nodes
      • take note of the node where you are logged to, ie. the head node, let's say niaWXYZ
      $ ssh  niagara.scinet.utoronto.ca
      USER@nia-login07:~$ salloc --nodes 5 --time=2:00:00
      .salloc: Granted job allocation 141862
      .salloc: Waiting for resource configuration
      .salloc: Nodes nia1265 are ready for job
      [USER@nia1265 ~]$
    2. On the second terminal:
      • ssh into niagara.scinet.utoronto.ca now using the -X flag in the ssh command
      • after that ssh -X niaWXYZ, ie. you will ssh carrying on the '-X' flag into the head node of the job
      • in the niaWXYZ you should be able to use graphics and should be redirected by x-forwarding to your local terminal
      ssh niagara.scinet.utoronto.ca -X
      USER@nia-login07:~$ ssh -X nia1265
      [USER@nia1265 ~]$ xclock   ## just an example to test the graphics, a clock should pop up, close it to exit
      [USER@nia1265 ~]$ module load ddt  ## load corresponding modules, eg. for DDT
      [USER@nia1265 ~]$ ddt  ## launch DDT, the GUI should appear in your screen


  • If you are using ssh from a Windows machine, you need to have an X-server, a good option is to use MobaXterm, that already brings an X-server included.
  • If you are in Mac OS, substitute -X by -Y
  • Instead of using two terminals, you could just use screen to request the resources and then detach the session and ssh into the head node directly.