Logging levels - meanings and use

All the popular logging frameworks follow the similar convention and naming for log levels. There are five priority levels in use.

Order ( high priority to low):
Meaning and Use:
  1. debug to write debugging messages which should not be printed when the application is in production.
  2. info for messages similar to the "verbose" mode of many applications.
  3. warn for warning messages which are logged to some log but the application is able to carry on without a problem.
  4. error for application error messages which are also logged to some log but, still, the application can hobble along. Such as when some administrator-supplied configuration parameter is incorrect and you fall back to using some hard-coded default value.
  5. fatal for critical messages, after logging of which the application quits abnormally.
 Additionally, there are two other levels. They have the obvious meanings.
  1. ALL
  2. OFF