The eight log levels of RFC 5424 (https://tools.ietf.org/html/rfc5424#page-11 ):

• 0 Emergency: system is unusable
• 1 Alert: action must be taken immediately
• 2 Critical: critical conditions
• 3 Error: error conditions
• 4 Warning: warning conditions
• 5 Notice: normal but significant condition
• 6 Informational: informational messages
• 7 Debug: debug-level messages