Data logging
Data logging is the practice of recording sequential data, often chronologically.
Etymology
To log is a verbed derivative of the noun logbook; the verb form means to record in a logbook, and may have been coined in the 1820s. The term logbook itself stems from the practice of floating a stationary "log" (actually a wooden block attached to a reel via rope) to provide a fixed point of reference for the purpose of measuring a ship's speed (see Knot (speed)). Computer scientists adopted the verb to log circa 1963 to describe the systematic recording of specific types of data processing events.
In Modern English, the noun log may refer to any systematic, chronological record of events.
Computer data logging
In computerized data logging, a computer program may automatically record events in a certain scope in order to provide an audit trail that can be used to diagnose problems.
Examples of physical systems which have logging subsystems include process control systems, and the black box recorders installed in aircraft.
Many operating systems and multitudinous computer programs include some form of logging subsystem. Some operating systems provide a syslog service (described in RFC 3164), which allows the filtering and recording of log messages to be performed by a separate dedicated subsystem, rather than placing the onus on each application to provide its own ad hoc logging system.
In many cases, the logs are esoteric and hard to understand; they need to be subjected to log analysis in order to make sense of them.
Other servers use a splunk to parse log files in order to facilitate troubleshooting; this approach may yield correlations between seemingly-unrelated events on different servers. Other enterprise class solutions such as those from LogLogic collect log data files in volume and make them available for reporting and real-time analysis.