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My sensors show an Unknown status after a PRTG core server service restart. What can I do?



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After restarting the PRTG core server service, but not the PRTG probe service, a lot of my sensors show an Unknown status. These sensors all have long scanning intervals. What is the reason for this behavior and why does PRTG not trigger a rescan of these sensors after the PRTG core server restart? What can I do?

prtg restart restart-service sensor-status unknown

Created on Jan 2, 2020 8:08:54 AM by  Maike Guba [Paessler Support]

Last change on Jan 3, 2020 8:49:43 AM by  Maike Guba [Paessler Support]

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This article applies as of PRTG Network Monitor 19

Reason for Unknown Status of Sensors after a PRTG Core Server Service Restart

Note: This issue only occurs if you restart the PRTG core server service without restarting the PRTG probe service at the same time.

Once the PRTG core server has restarted, it loads and displays the sensor states of those sensors whose last scan was performed less than 5 minutes ago. Because the PRTG probe service was not restarted, the probes have still been collecting data during the restart of the PRTG core server according to their original schedule. Depending on a sensor’s scanning interval, it might take several minutes, hours, or days until the probe triggers a new sensor scan and sends the sensor’s data to the PRTG core server.

A sensor with a scanning interval that is longer than 5 minutes therefore shows an Unknown status until its next scheduled sensor scan.

Troubleshooting Solutions

To solve this issue,

  • restart the PRTG probe service as well. The probe then automatically performs a new scan of all sensors when connecting to the PRTG core server.
  • manually scan the affected sensors by using the Scan Now option from the context menu. This triggers an unscheduled sensor scan at the probe.


Created on Jan 2, 2020 8:15:04 AM by  Maike Guba [Paessler Support]

Last change on Jan 3, 2020 8:51:14 AM by  Maike Guba [Paessler Support]

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Disclaimer: The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.