A system and associated method for utilizing file names for diagnostic data files generated by a runtime environment. The method employs a file counter base that defines a predefined maximum number of files permitted in a file system, a generation number that indicates an instance of the runtime environment, and a file counter that comprises a file name. The file counter circulates by a cycle equal to the file counter base such that the file system uses only a limited disk space. The method determines the generation number per instance of the runtime environment by examining file counters of existing files in the file system. The generation number initializes the file counter for creating file names in the instance of the runtime environment. The method guarantees a longest life span of a diagnostic data file in a file system that has a limited number of files.