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Why do I encounter gaps in the graphs/data of my EXE sensors?



Why do I encounter gaps in the graphs or data of my EXE sensors? Why do I get the error Limit of 100 parallel .exe – Sensors reached?

What causes this error and what can I do about it?

error exe graphs prtg

Created on Sep 8, 2017 6:30:45 AM by  Brandy Greger [Paessler Support]

Last change on May 22, 2019 12:27:11 PM by  Maike Guba [Paessler Support]

3 Replies

Accepted Answer



This article applies to PRTG Network Monitor 19 or later

Limit of 100 Parallel EXE Sensors Error

If you have received the following error in your probe log

Limit of 100 parallel .exe – Sensors reached for x times. DROPPING SEVERAL REQUESTS for system stability

although the CPU load has not reached a critical level, this is not an error caused by exhaustion of your hardware, but rather a preventive limit that has been set within PRTG itself to avoid an unexpected termination of processes.

PRTG has a limit of 100 concurrent parallel EXE sensor-based scans. This includes PowerShell, batch, and other script-based custom sensors.

Reason for the Limitation

Windows defines a limited user land memory space or desktop heap memory for each user, service, or process. This practically limits the number of parallel child processes that can be running at the same time, among other things.
The default values Windows defines for a process that is running as a local system causes the termination of random child processes when approximately 120 child processes are running. Depending on the task or function these killed processes were running at the termination time, the result could be fatal.

PRTG limits the maximum amount of concurrent parallel EXE-based scans to 100. This is because terminating processes, in particular with regards to the EXE-based sensors, can lead to corrupt systems because allocated semaphores or mutexes cannot be released, for example.

This limitation is designed to keep a smooth flow of the scans on the probe. Normally, this limitation only applies in exceptional cases, even when systems have a heavy load. This can be the case if, for example, the core probe is reconnected and as a result, an initial rescan is carried out in the course of the schedule sequence, or if a large number of target systems is restarted.


Move the EXE sensors to multiple remote probes

Moving these sensors to remote probes can relieve the core server. The core server then only has to make the calculations and preparations, and therefore does not have to actually execute the EXE sensors. For more information, see PRTG Manual: Remote Probes and Multiple Probes.

Increase the scanning interval

Increasing the scanning interval to 10 or 15 minutes, for example, can help distribute the sensors more efficiently. This is only useful when you have less than 1,000 EXE sensors deployed in your monitoring setup. For more information, see PRTG Manual: System Administration—Monitoring.

Other Solutions

Note: These solutions are only a last resort if the other solutions could not solve the issue or are not applicable.

  • To increase the limitation count in the probe in question, contact our support via the PRTG web interface under Setup | Contact Support.
  • To increase the desktop heap size in Windows, you have to modify the heap allocation sizes accordingly.

Important: We do not recommend modifying the registry because incorrect modification can cause serious issues. Please ensure that you have backed up the registry before you continue. For more information, see How to back up and restore the registry in Windows.

  1. Open the registry editor.
  2. Navigate to the following registry subkey: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\SubSystems
  3. Right-click the Windows entry and click Modify.
  4. In the Value Data section of the Edit String dialog box, locate the SharedSection entry. Increase the second value and the third value for this entry.

For more information, see the Microsoft article You may receive an "Out of Memory" error message because of the desktop heap limitation.


For more information on desktop heaps, see Desktop Heap Overview.

Created on Sep 8, 2017 7:11:26 AM by  Brandy Greger [Paessler Support]

Last change on May 22, 2019 12:43:16 PM by  Maike Guba [Paessler Support]



Is there a possibility to monitor current number of parallel exes running? Best possible with API call.

We see this problem time to time on one of our probe and I would like to be able to get notification as soon as this occurs.

Log says: There are XX .exe sensors slots free at the moment

Do you expose this value somehow? i would like to avoid parsing file using additional Powershell script.

Created on Jul 30, 2019 8:33:51 AM



Hi there,

The value is not offered somewhere. But as a rule of thumb, if this message appears in the log, then you have too much exe based sensors running or the exe based sensors run with a too low scanning interval. In either way, something needs to be changed.

You either split the exe based sensors across multiple probes or you increase the scanning intervals to at least 5, better 10, minutes.

Best regards.

Created on Jul 30, 2019 10:01:54 AM by  Dariusz Gorka [Paessler Support]

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.