A tracing package for the UNIX file system has been implemented and statistics have been gathered from a heavily and widely used DEC VAX 11/780 running UNIX 4.2BSD. This tracing package is unusual in the comprehensiveness of the data gathered, the clean and usable format in which the final trace appears, and the use of a post processing step to assemble information in trace records that is not easily (or at all) available at trace time. Trace records are gathered for file opens, file creates, file closes, reads and writes, renames, file deletes, executes, forks and exit calls. Some preliminary analyses of the trace data are presented. We found that the I/O activities are very bursty, that very few read and write operations are performed in most of the open-close sessions, and that the process lifetime distribution is highly skewed, with many short lived processes and a few long term ones. The extensive data gathered using the package is valuable for the studies of disk caching and file migration algorithms, distributed file system performance, and load balancing strategies.