Werk #19226: Windows agent now accepts connections right after a fresh installation
| Component | Checks & agents | ||
| Title | Windows agent now accepts connections right after a fresh installation | ||
| Date | Sep 25, 2026 | ||
| Level | Prominent Change | ||
| Class | Bug Fix | ||
| Compatibility | Compatible - no manual interaction needed | ||
| Checkmk versions & editions |
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After a fresh installation, the Windows agent did not answer queries. Nothing was listening on port 6556, even though the firewall rule had been created. Restarting the Checkmk service was required to make the agent respond. This affected agents that had not been registered yet.
The cause was an ordering problem between the agent service and the agent controller. The service created the marker file that permits unregistered pull mode only after it had already started the controller, and the controller reads that marker exactly once, at its own startup. It therefore saw no marker and no registration, and kept the port closed for the rest of its lifetime. A restart helped because the marker was on disk by then.
The service now creates the marker before it starts the controller, and the controller re-checks the marker for as long as the port stays closed, so a late marker is picked up without a restart.
Starting with this release, the agent accepts connections immediately after installation. No restart is needed.