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With dramatic improvements in cost-performance, the use of clusters of personal computers is becoming widespread. For ease of use and management, a single system image (SSI) is highly desirable. There are several approaches that one can take to achieve SSI. In this paper, we discuss the achievement of SSI via the use of the user login shell. To this end, we describe shoc (shell over a cluster)-an implementation of the standard Linux-GNU bash shell that permits the user to utilize a cluster as a single resource. In addition, shoc provides for transparent pre-emptive load balancing without requiring the user to rewrite, recompile or even relink of existing applications. Running at user-level, shoc does not require any kernel modification and currently runs on any Linux cluster fulfilling a minimal set of requirements. We also present results on the performance of shoc and show that the load balancing feature gives rise to better overall cluster utilization as well as improvement in response time for individual processes.