Testing With Graphics

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This article is a draft

This is not a complete article: This is a draft, a work in progress that is intended to be published into an article, which may or may not be ready for inclusion in the main wiki. It should not necessarily be considered factual or authoritative.

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.