Werk #19192: Windows agent: disable WinDbg logging by default

Component	Checks & agents
Title	Windows agent: disable WinDbg logging by default
Date	Mar 24, 2026
Level	Trivial Change
Class	New Feature
Compatibility	Incompatible - Manual interaction might be required
Checkmk versions & editions	2.6.0b1 Not yet released Checkmk Community, Checkmk Pro, Checkmk Ultimate, Checkmk Cloud, Checkmk Ultimate MT 2.5.0b2 Checkmk Community, Checkmk Pro, Checkmk Ultimate, Checkmk Cloud, Checkmk Ultimate MT 2.4.0p26 Checkmk Community, Checkmk Pro, Checkmk Ultimate, Checkmk Cloud, Checkmk Ultimate MT

Previously, the Windows agent sent all log messages to the Windows debugging interface (WinDbg / OutputDebugString) by default. This meant that on every production host running the Checkmk agent, log output was continuously written to the debug sink — even when no debugger was attached and nobody was monitoring it.

This behavior is undesirable in production environments for two reasons: first, OutputDebugString has a non-trivial overhead when a debugger is attached, and second, it exposes internal agent log messages to any process that listens on the debug output channel (e.g. DebugView, WinDbg).

WinDbg logging is now disabled by default. It can be re-enabled explicitly by setting windbg: yes under global.logging in the agent configuration file, which is appropriate for development and debugging scenarios.

Installations that relied on WinDbg or DebugView capturing agent output by default must explicitly set windbg: yes in the agent configuration after upgrading.

To the list of all Werks