1. A method of executing an accelerator application program on an accelerator in a hybrid computing environment, the hybrid computing environment comprising: a host computer and an accelerator, the host computer and the accelerator adapted to one another for data communications by a system level message passing module; the method comprising: receiving, by the system level message passing module from a host application program on the host computer, operating information for the accelerator application program, the operating information including a value of a substitution variable identifying a current working directory (‘CWD’) for the accelerator application program; designating, by the system level message passing module, a directory as a CWD for the accelerator application program, separate from any other CWDs of any other applications running on the accelerator; assigning, by the system level message passing module to the CWD, a name that is unique with respect to names of other CWDs of other applications in the computing environment.