Werk #22278: Special agents: fix race condition when storing data between runs

Component

Checks & agents

Title

Special agents: fix race condition when storing data between runs

Date

Sep 30, 2026

Level

Trivial Change

Class

Bug Fix

Compatibility

Compatible - no manual interaction needed

Checkmk versions & editions

3.0.0b1 Not yet released	Checkmk Community, Checkmk Pro, Checkmk Ultimate, Checkmk Cloud, Checkmk Ultimate MT
2.5.0p15	Checkmk Community, Checkmk Pro, Checkmk Ultimate, Checkmk Cloud, Checkmk Ultimate MT

Special agents and active checks that keep data between runs could read an empty or incomplete value when two runs for the same host overlapped (for example a service discovery during a regular check). Depending on the plug-in, this caused a crash or a lost cache for:

Amazon Web Services (AWS)
Azure, Azure (deprecated)
Bazel remote cache
Check email, Check email delivery, Check IMAP/EWS/GraphApi mailboxes
Cisco Meraki
Gerrit
Kubernetes
Proxmox VE
Redfish compatible management controller, Redfish compatible power equipment (PDU)
VMware ESX via vSphere

This data is now written atomically, so a concurrent run sees either the old or the new content.

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