Logging levels

RFC 5424 (The Syslog Protocol) defines the severity levels in section 6.2.1:

Numerical Code Severity
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

Severity examples for web applications

Severity Description Examples
Emergency System is unusable
Alert Action must be taken immediately
Critical Critical conditions
Error Error conditions
Warning Warning conditions
Notice Normal but significant condition
Informational Informational messages
Debug Debug-level messages