Running gdb on the compute node

You can debug the application directly on the compute node by logging in to it and attaching to the process with gdb. We don't recommend this to users, but administrator's may wish to do this from time to time.

If you need to attach to the process at it's very start, there are four points in the application process where you can do this:

• Right after the PCT forks the application process
• After the PCT sets up the application process uid/gid information but before it exec's the application code
• Right after the application code begins execution but before it executes any of it's Cplant startup code.
• After the application process has executed it's Cplant startup code but just before it begins executing the user's code.

Choose the nodes you want to run on by using the -l option to yod. Then use the -sleep option to choose one of the four points at whilch to attach to the code. Then you have 60 seconds in which to log in to the compute node and attach gdb to the process.