Logging is the tracking of application events of a system into one or more log files in parallel to execution. Instead of writing to a file writting to stdout on Linux installations is possible, so that log information can be picked up by a specialized monitoring solution.
Events for logging may refer to receiving a request from an external sender, starting or ending the processing of a task, the system raising an error or exception, or other, so that in case of an issue with the system, the processing can be reconstructed and analyzed.
The logging behavior can be configured in order to produce more log information, e.g. when reproducing an issue, or less, e.g. in a well-running production system. Besides the log row format, there is the configuration of the log level (i.e. only tracking error-events respectively tracking error-, warning-, information- and debug messages), as well as the configuration of which system component should be traced.
Also, configurable is how log files are organized (i.e. start every day a fresh log file) and how long they are getting kept (i.e. remove after 7 days, or when a limit for disc space allocation by log files is exceeded). This configuration is typically referred to as “log rotation”.