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What to check if sensors are gray?

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My PRTG installation shows gray sensors in an Unknown state. What does this sensor status mean?

gray prtg sensor-status sensors unknown

Created on Sep 30, 2011 8:27:12 AM by  Daniel Zobel [Paessler Support]

Last change on Sep 11, 2019 7:29:06 AM by  Florian Weik [Paessler Support]



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This article applies to PRTG Network Monitor 19 or later

Unknown (Gray) Sensors

There can be various reasons why sensors show an Unknown status. See the sections below for more information on what you can check if you see permanently unknown (gray) sensors in your setup. Referring to these points will also help with debugging when you contact our support team.

Narrowing Down Circumstances

Try to find a common denominator among your unknown sensors.

  • Which sensors are gray?
    • All sensors
    • All sensors of a probe
    • All sensors of a specific type (for example, SNMP or WMI)
    • All sensors of a device
    • All sensors in a specific network segment
    • Various sensors in various groups, devices, probes
  • Are you using a cluster?
  • Is the PRTG Probe Service running on the parent probe machine?

Step 1: If the Probe Service Is Not Running

If the PRTG Probe Service (PRTG Probe.exe) is not running, please do the following.

Reboot the System

Sometimes a simple system reboot makes your monitoring system function correctly again.

Check the Executables

In your PRTG program folder, right-click on the files PRTG Server.exe and PRTG Probe.exe. From the Windows context menu, select Properties. In the Version tab, the Product Version number must fit the one you installed with the PRTG setup file (for example, if you installed a PRTG 13 version, the version number should not show a PRTG 12 version).

Check the Probe Logfile

In your PRTG program directory, check the PRTG Probe Log (x).log file in your Logs (System) folder. Does it give any hints on connection or overload problems? If you find irregularities, open a support ticket.

Check the Windows Event Log Entries

On the computer that is running the PRTG core server or a remote probe, check the Windows Event log for entries such as access violations of PRTG services or their unexpected termination.

Step 2: If the Probe Service Is Running

If you see that the PRTG Probe Service (PRTG Probe.exe) is running, do the following:

Check the Outgoing IP of the Probe

On the computer running the PRTG core server or the remote probe, open the PRTG Administration Tool from the Windows start menu. Select the Probe Settings for Monitoring tab and make sure the probe uses the correct outgoing IP to connect to the devices in your network. In most cases, the auto setting will be fine!

Note: In previous PRTG versions, use the Outgoing IP Settings tab of the Probe Administrator program for this purpose.

Wait at Least 1 Hour

In some scenarios, for example when using a cluster or many WMI sensors, it may take a while until all sensors receive data and therefore switch to a green Up status, especially with a scanning interval of 5 minutes or more. Please be patient and wait a little longer, because sometimes it simply takes some time for your monitoring to (re-)start.

Create Two Probe Status Files

In the PRTG web interface, go to Setup | System Administration | Administrative Tools. In the Administrative Tools for Probes section, go to Write Probe Status Files and click the Go! button. This will write probe status text files to the Logs (System) directory of your PRTG program directory.

Wait 2 minutes, then click the Go! button for Write Probe Status Files again.

2.1 If No Probe Status Files Are Generated

If these files are not written to the PRTG program directory, the probe hangs or there is a communication problem. Do the following:

Restart the System

Restart your PRTG core server or the computer running the remote probe and try writing probe status files again.

Check the Probe Logfile

If the status files are still not written, check the PRTG Probe Log (x).log file in the Logs (System) folder of your PRTG program directory. Does it give any hints on connection or overload problems? If you find irregularities, open a support ticket.

Check the Probe Connection State

In the PRTG web interface, go to Setup | System Administration | Administrative Tools. In the Administrative Tools for Probes section, check the connection status of the local probe and remote probes, if any.

Check the Connection from the Remote Probe System

If your unknown sensors are on a remote probe, log in to the computer running the remote probe. From this server, try to ping the PRTG core server to check if a connection is possible, and if DNS resolution and routing work correctly. Make sure that connections are not blocked by server or firewall settings. Also check firewall and virus scanner settings on both the PRTG core server and the system running the remote probe.
Note: In some cases, pings are intentionally disabled on the server or firewall, but connections between PRTG core server and remote probes can work anyway.

Check the Number of Threads of the Probe

On the PRTG core server or the system running the remote probe, open the Windows Task Manager. From the menu, choose View | Select Columns and activate the column for Threads. Show the processes of all users and in the Processes tab, look at the number of threads for the PRTG Probe process. Values > 200 are conspicuous.

2.2 If Probe Status Files Are Generated

If the probe status files are written to the PRTG program directory, do the following:

Check Time Stamps

Look at two probe status files and check if the time stamps of an unknown sensor change between two probe states.

Check the Probe Logfile

In your PRTG program directory, check the PRTG Probe Log (x).log file in your Logs (System) folder. Does it give any hints on connection or overload problems? If you find irregularities, open a support ticket.

Check the Probe Health Sensor

In the PRTG web interface, open the details view of the Probe Health sensor and check the number of open requests and messages. Open requests that are constantly > 100 or messages that are constantly > 50 should be further investigated.

Recalculate the Cache

As of PRTG 14.1.9, you can recalculate the cache under Setup | System Administration | Administrative Tools.

In PRTG versions previous to 14.1.9, do the following: On the PRTG core server, open the PRTG Server Administrator from the Windows start menu. In the Memory Usage tab, add a check mark for Recalculate cache now, click on Ok, and confirm restarting services.

Check Time Settings

In the PRTG web interface, check the time of the last data in the Live Data table of the unknown sensors. If a sensor contains data from the future (which means that a wrong time was set in the system), all data until this time is disregarded by the core.

Created on Sep 30, 2011 11:25:40 AM by  Daniel Zobel [Paessler Support]

Last change on May 20, 2019 10:17:44 AM by  Brandy Greger [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.