This paper describes the components of a runtime system for launching parallel applications and presents performance results for starting a job on more than a thousand nodes of a workstation cluster. This runtime system was developed at Sandia National Laboratories as part of the Computational Plant (Cplant TM ) project, which is deploying large-scale parallel computing clusters using commodity hardware and the Linux operating system. We have designed and implemented a flexible runtime system that allows for launching parallel jobs on thousands of nodes in a matter of seconds. The interactions of the components are described, and the key issues that address the scalability and performance of the runtime system are discussed. We also present performance results of launching executables of varying sizes on more than a thousand nodes.