#17 PLC Best Practices – Log PLC Uptime and Trend it on HMI

Log PLC uptime to know when it’s been restarted. Trend and log uptime on the HMI for diagnostics.

Security ObjectiveTarget Group
MonitoringIntegration / Maintenance Service Provider

Log PLC Uptime

Keep track of programmable logic controller uptime

  • in the PLC itself (if uptime is a system variable in the PLC)
  • in the PLC itself if it has MIB-2 / any SNMP implementation
  • externally by means of e.g., SNMP

If the PLC has SNMP with MIB-2, which is very common, the OID for uptime “sysUpTimeInstance(0)” is

Uptime resets are important indicators for PLC restarts. Make sure the HMI alerts to any sort of PLC restart.

Uptime correlated with error codes are good diagnostics.




Beneficial for…?Why?
      SecurityThe most basic attack vector for a PLC is to force it to crash and/or restart.

For many PLCs, it is not that hard to do, because many PLCs cannot cope well with unexpected inputs or too much traffic.

Thus, unexpected restarts can be an indicator that the PLC encounters unusual actions.
  ReliabilityPLC restarts are also good for diagnostics in case of failures and for monitoring which PLCs are being worked on at what time.


MITRE ATT&CK ICSTactic:  TA009 – Inhibit Response Function
Technique:  T0816 – Device Restart/Shutdown
ISA 62443-3-3SR 7.6: Network and security configuration settings
ISA 62443-4-2CR 7.6: Network and security configuration settings
MITRE CWECWE-778: Insufficient Logging

Source: PLC Security

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