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## Setting up the parallel environment

VisIt is usually executed by a script called: visit, which sets up the environment variables required for VisIt to execute. When the visit script is told to launch a parallel compute engine, it sets up the environment variables as it usually does and then invokes an appropriate parallel launch program that takes care of either spawning the VisIt parallel compute engine processes or scheduling them to run in a batch system. When VisIt is used with MPICH on some clusters, the parallel launch program does not replicate the environment variables that the visit script set up, preventing the VisIt parallel compute engine from running. On clusters where the parallel launch program does not replicate the VisIt environment variables, VisIt provides an option to start each process of the VisIt compute engine under the visit script. This ensures that the environment variables that VisIt requires in order to run are indeed set up before the parallel compute engine processes are started. To enable this feature, click on the Use VisIt script to set up parallel environment check box on the Host profiles Window's Advanced options tab.