Interpreting log files

The log files provide some of the best clues as to what is going on when a system doesn't act as expected. Depending on the verbosity level configured and whether or not NGINX was compiled with debugging support (--enable-debug), the log files will help you understand what is going on in a particular session.

Each line in the error log corresponds to a particular log level, configured using the error_log directive. The different levels are debug, info, notice, warn, error, crit, alert, and emerg, in order of increasing severity. Configuring a particular level will include messages for all of the more severe levels above it. The default log level is error.

In the context of the mail module, we would typically want to configure a log level of info so that we can get as much information about a particular session as possible without having to configure debug logging. Debug logging, in this case, would be useful only for following function entry points, or seeing what...