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What to check if sensors are black (gray)?

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My PRTG installation show black sensors in an Unknown state. What is this sensor status about?

black gray prtg sensor-status sensors unknown

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



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This article applies to PRTG Network Monitor 14 or later

Black (Gray) Sensors

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

0 Narrowing Down Circumstances

Please try to find a commonality among your black sensors.

  • Which sensors are grey?
    • all sensors
    • all sensors of a probe
    • all sensors of a specific type (e.g., SNMP or WMI)
    • all sensors of a device
    • all sensors in a specific network segment
    • various sensor in various groups, devices, probes
  • Are you using a cluster?
  • Is the PRTG Probe Service running on the parent probe machine?

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 causes your monitoring system to function correctly again.

Check the Executables

In your PRTG program folder, right-click on the files PRTG Server.exe and PRTG Probe.exe and from the Windows context menu, select Properties. In the Version tab, make the Product Version number fits 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 Log File

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

Check the Windows Event Log Entries

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

2 If the Probe Service Is Running

If you see the PRTG Probe Service (PRTG Probe.exe) running, please 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. On the Probe Settings for Monitoring tab, please make sure the probe uses the correct outgoing IP to connect to the devices in your network. In most cases the "auto" setting should 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 OK 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 Probe Administrative Tools 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 data folder.

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

2.1 If No Probe Status Files Are Generated

If those files are not written to the PRTG data folder, the probe hangs, or there is a communication problem. Please do the following.

Restart System

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

Check the Probe Log File

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

Check Probe Connection State

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

Check Connection from Remote Probe System

If your black sensors exist 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 DNS resolution and routing work correctly. Make sure that connections are not blocked by server or firewall settings. Check also 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/firewall; connections between PRTG core server and remote probes can work anyway).

Check 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 state files are written to the PRTG data folder, please do the following.

Check Time Stamps

Look at 2 files probe state files and check if the timestamps of a black sensor change between two probe states

Check the Probe Log File

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

Check 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 constantly > 100 or messages 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 black sensors. If a sensor contains data from the future (there was a wrong time set in the system) all data until this time is passed is disregarded by the core.

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

Last change on Feb 18, 2015 1:45:12 PM by  Gerald Schoch [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.