Analysis of failures in the Tandem NonStop-UX Operating System

The paper presents results from an investigation of failures in several releases of Tandem's NonStop-UX Operating System, which is based on Unix System V. The analysis covers software failures from the field and failures reported by Tandem's test center. Fault classification is based on the status of the reported failures, the detection point of the errors in the operating system code, the panic message generated by the systems, the module that was found to be faulty, and the type of programming mistake. This classification reveals which modules in the operating system generate the most faults and the modules in which most errors are detected. We also present distributions of the failure and repair times including inter arrival time of unique failures and time between duplicate failures. These distributions, unlike generic time distributions, such as time between failures, help characterize the software quality. Distribution of the repair times emphasizes the repair process and the factors influencing repair. Distribution of up time of the systems before the panic reveals the factors triggering the panic.