The data contents of an information system may be corrupted due to security breaches or human errors. This project focuses on intrusion tolerance techniques that speed up the process of repairing a damaged file system. The proposed system, called Repairable File Service (or RFS), is specifically designed to facilitate the repair of compromised network file servers. An architectural innovation of RFS is that it is decoupled from and requires no modifications on the shared file server that is being protected. RFS supports fine-grained logging to allow roll-back of any file update operation, and keeps track of inter-process dependencies to quickly determine the extent of system damage after an attack/error. Compared with the current practice of manual post-intrusion damage repair, RFS significantly reduces the mean time to repair and thus improves the overall system availability. Performance overhead of RFS is less than 6%.