This paper provides a brief overview of techniques and tools being developed for monitoring and predicting the performance of Unix server congurations for given real-life workloads. We show how our system call trace mechanism, called Ultra, captures a complete trace of a process's calls to the operating system with only minimal interference to the system under study. Once captured, the traces can be used to reproduce the captured workload's behaviour in full. Rerunning such multi-process workloads from their traces is complicated because the inter-dependencies between the activities of the individual constituent processes must be reproduced correctly if the overall behaviour of the workload is to be reproduced successfully. We show how our approach can be extended to meet this requirement, and allow multi-process workloads to be traced and rerun. To illustrate the usefulness of our tools, we present a case study in which our traces are used to predict the impact of le s..