What is Logging?
Logging is the process by which systems, devices or applications automatically record events in log files. These logs contain information about what happened, when and by whom or what it was triggered.
Logging forms the basis for Monitoring, troubleshooting, auditing and Cybersecurity — in both IT and OT.
🧠 What does a log file contain?
A log entry typically contains:
- Timestamp
- Source (e.g. server, application, network device)
- Event type (info, warning, error)
- Description of the event
- Sometimes: IP address, user name, process ID, etc.
📂 Examples of logging
| Domain | Examples of logs |
|---|---|
| System | Boot errors, disk problems, user logins |
| Network | Firewall traffic, VPN connections, port scans |
| Applications | Error messages, transaction logs, authentication attempts |
| OT systems | PLC status, alarm messages, operator actions |
| Security | SIEM, IDS, EDR, Access Control logs |
🔧 Log levels (severity)
Many logs use levels such as:
- INFO – ordinary status messages
- WARNING – possible issue
- ERROR – fault requiring intervention
- DEBUG – detailed information for developers
- CRITICAL – serious failure or security incident
🔐 Why is logging important?
- Audit trail for forensic investigation
- Incident detection during cyber attacks
- Compliance (e.g. ISO 27001, NIS2, GxP)
- Monitoring of system performance and reliability
- Analysis of user or operator behaviour
🛠 Tools for log management
- Log collectors: Syslog, journald, Windows Event Log
- Analysis tools: SIEM, the ELK stack, Graylog, Splunk
- Alerting: combine with dashboards or triggers for suspicious activity
📌 In summary
Logging is essential for understanding what is happening within your systems. It supports both technical diagnostics and security monitoring, and forms the backbone of SIEM solutions and audit trails.