Long term monitoring of the VST through telescope log data

Every night the VST Telescope Control Software logs large text files including information on the telescope and instrument operations, executed commands, failures, weather conditions and anything is relevant for the instrument maintenance and the identification of problem sources. These log files are a precious tool, daily used by the observatory personnel for the analysis of any issue raised by the telescope operators during the night. One of the most frequent use of these data is then to trace back telescope, instrument or enclosure problem sources and analyze them. Consequently, these _les are often analyzed looking only for specific issues and for solving well identified problems, in the framework of dedicated and focused efforts. Thus, a minimal part of the information is useful for this kind of daily maintenance. Nevertheless, the log files contain a gold mine of other data, which often make sense only when analyzed on a long time span. This paper describes a 5-year effort, started in 2015, for the systematic collection and analysis of log files, aiming at the identification of useful long-term trends and statistics which are normally overlooked in the daily telescope life. The specific case of the active optics open-loop corrections is discussed as case study.