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RFC5424 / syslogApache,
bunyan		JavaScript Consolenpm, winstonAngularJS $log
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fatal (60)
"fatal" (60): The service/app is going to stop or become unusable now. An operator should definitely look into this soon.
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emerg (0)
system is unusable
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alert (1)
action must be taken immediately
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crit (2)
critical conditions
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error (3)
error conditions		error (50)errorerror (0)error
"error" (50): Fatal for a particular request, but the service/app continues servicing other requests. An operator should look at this soon(ish).
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warning (4)
warning conditions		warn (40)warnwarn (1)warn
"warn" (40): A note on something that should probably be looked at by an operator eventually.
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notice (5)
normal but significant condition
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info (6)
informational messages		info (30)info
Informative logging information		info (2)info
"info" (30): Detail on regular operation.
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verbose (3)
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log
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debug (7)
debug-level messages		debug (20)debug (4)debug
"debug" (20): Anything else, i.e. too verbose to be included in "info" level.
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trace (10)
"trace" (10): Logging from external libraries used by your app or very detailed application logging.
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silly (5)
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Interesting reads:
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http://stackoverflow.com/questions/7839565/logging-levels-logback-rule-of-thumb-to-assign-log-levels
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