| Code | Display | Definition |
| emergency | Emergency | System is unusable. e.g., This level should only be reported by infrastructure and should not be used by applications. |
| alert | Alert | Notification should be sent to trigger action be taken. e.g., Loss of the primary network connection needing attention. |
| critical | Critical | Critical conditions. e.g., A failure in the system's primary application that will reset automatically. |
| error | Error | Error conditions. e.g., An application has exceeded its file storage limit and attempts to write are failing. |
| warning | Warning | Warning conditions. May indicate that an error will occur if action is not taken. e.g., A non-root file system has only 2GB remaining. |
| notice | Notice | Notice messages. Normal but significant condition. Events that are unusual, but not error conditions. |
| informational | Informational | Normal operational messages that require no action. e.g., An application has started, paused, or ended successfully. |
| debug | Debug | Debug-level messages. Information useful to developers for debugging the application. |