System Logging Explained
1. Key Concepts of System Logging
System Logging is a critical function in network management that records events and activities on a network device. Key concepts include:
- Log Levels: Different severity levels for log messages.
- Log Destinations: Where log messages are sent (e.g., local file, remote server).
- Log Categories: Specific types of events that are logged.
- Log Rotation: Managing and archiving log files to prevent them from becoming too large.
2. Log Levels
Log levels define the severity of log messages. Common log levels include:
- 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.
Example: If a network device detects a critical error, it will generate a log message with a "Critical" level, alerting administrators to take immediate action.
3. Log Destinations
Log destinations determine where log messages are sent. Common destinations include:
- Local File: Logs are stored on the device's local storage.
- Remote Server: Logs are sent to a centralized logging server over the network.
- Console: Logs are displayed directly on the device's console.
- Email: Logs are sent via email to administrators.
Example: In a large enterprise network, logs from all devices might be sent to a centralized logging server for easier monitoring and analysis.
4. Log Categories
Log categories specify the types of events that are logged. Common categories include:
- System: General system events.
- Security: Security-related events (e.g., login attempts).
- DHCP: DHCP server events.
- Firewall: Firewall rule matches and actions.
- Interface: Interface status changes and errors.
Example: If you want to monitor DHCP lease assignments, you would enable logging for the "DHCP" category to capture all related events.
5. Log Rotation
Log rotation is the process of managing log files to prevent them from becoming too large. This involves archiving old logs and creating new log files. Key aspects include:
- Size-based Rotation: Rotate logs when they reach a certain size.
- Time-based Rotation: Rotate logs at regular intervals (e.g., daily, weekly).
- Retention Policy: Define how long logs are kept before being deleted.
Example: A network device might be configured to rotate log files daily and retain logs for 30 days. After 30 days, old logs are automatically deleted to free up storage space.