EVOSS is a model-based approach to support the upgrade of FOSS systems. EVOSS promotes the simulation of upgrades to predict failures before affecting the real system. Both fine-grained static aspects (e.g. configuration incoherences) and dynamic aspects (e.g. the execution of configuration scripts) are taken into account, improving over the state of the art of package managers. 

The simulator is able to simulate also pre and post installation scripts that equip each distribution package. This is possible thanks to a domain specific language (DSL), which has been conceived within EVOSS to specify maintainer scripts behavior. The output of Upgrade Simulator is a new System Configuration Model if no errors occur during the simulation, otherwise an Incoherences Report is produced. The new System Configuration Model is queried and analyzed by the Failure Detector component. The Fault Detector component offers a fully automatic, cost-effective and pragmatic way of improving the quality of the system.