DDT is a parallel debugger with a straightforward graphical interface. After setting up DDT for our environment (more on this below) there are only a few steps to using it:

• Make sure you are running an X-Windows server on your computer.
• When logging into nyx-login, make sure you have enabled X-forwarding in your ssh client; you can confirm this is working by typing echo $DISPLAY after logging into nyx and you should see something similar to localhost:10.0, if you don't see that, you can't yet start DDT. (For more information on X-servers and X-forwarding on Windows, see CAEN's Technote Introduction to X11.)
• Compile your code with -g to include debugging symbols.
• Load the DDT module by typing: module load ddt
• Start DDT with your code by typing: ddt myprogram then when prompted select the number of MPI processes you want to run and press "Run".

This will run DDT on the head-node. If you have access to private nodes, you should try to run DDT on those nodes. To do that, insert this step before starting DDT.

• Start an interactive PBS job including X-forwarding with the command:
  qsub -N debug -q myQueue -l nodes=4:ppn=2,walltime=04:00:00 -I -V -X

For more information, see the Quickstart Guide for C Programs, Quickstart Guide for Fortran Programs, or the DDT User Guide.

Running DDT for the first time

When DDT starts for the first time, you'll need to answer a few questions.

DDT cannot open the configuration file

Choose "Create a new file"

A "wizard" will start

Click "Next"

You will need to chose an MPI Implementation

Unless you know otherwise, you should choose OpenMPI from the drop-down menu and press "Next"

The next question is to chose a list of compute nodes to run on

You should not choose any nodes; to do this select "Do not configure DDT for attaching at this time" click and "Next"

This is the end of the wizard

Click "Finish"

After this you will be put into DDT where you can chose the number of processes to run and press "Run"