Windows agent repeatedly loosing connection

Troubleshooting
,
1

CMK version:2.2.0p41
OS agent version: Microsoft Windows Server 2019

Error message:

2025-06-06 07:34:07.702 [ctl:4424] [cmk_agent_ctl::modes::pull][DEBUG] processed task!

2025-06-06 07:35:07.275 [ctl:4424] [cmk_agent_ctl::modes::pull][INFO] [::ffff:10.0.xx.xx]:48578: Handling pull request.

2025-06-06 07:35:07.306 [ctl:4424] [cmk_agent_ctl::modes::pull][DEBUG] [::ffff:10.0.xx.xx]:48578: Handling pull request DONE (Task detached).

2025-06-06 07:35:07.337 [ctl:4424] [cmk_agent_ctl::mailslot_transport][WARN] Error server mailslot name Global\WinAgentCtl_4424_7656_0 is in use, retry...

2025-06-06 07:35:07.369 [ctl:4424] [cmk_agent_ctl::mailslot_transport][WARN] Error server mailslot name Global\WinAgentCtl_4424_7656_1 is in use, retry...

2025-06-06 07:35:07.400 [ctl:4424] [cmk_agent_ctl::mailslot_transport][WARN] Error server mailslot name Global\WinAgentCtl_4424_7656_2 is in use, retry...

2025-06-06 07:35:07.421 [ctl:4424] [cmk_agent_ctl::mailslot_transport][WARN] Error server mailslot name Global\WinAgentCtl_4424_7656_3 is in use, retry...

2025-06-06 07:35:07.453 [ctl:4424] [cmk_agent_ctl::mailslot_transport][WARN] Error server mailslot name Global\WinAgentCtl_4424_7656_4 is in use, retry...

2025-06-06 07:35:07.485 [ctl:4424] [cmk_agent_ctl::mailslot_transport][WARN] Error server mailslot name Global\WinAgentCtl_4424_7656_5 is in use, retry...

2025-06-06 07:35:07.516 [ctl:4424] [cmk_agent_ctl::mailslot_transport][WARN] Error server mailslot name Global\WinAgentCtl_4424_7656_6 is in use, retry...

2025-06-06 07:35:07.547 [ctl:4424] [cmk_agent_ctl::mailslot_transport][WARN] Error server mailslot name Global\WinAgentCtl_4424_7656_7 is in use, retry...

2025-06-06 07:35:07.578 [ctl:4424] [cmk_agent_ctl::mailslot_transport][WARN] Error server mailslot name Global\WinAgentCtl_4424_7656_8 is in use, retry...

2025-06-06 07:35:07.609 [ctl:4424] [cmk_agent_ctl::mailslot_transport][WARN] Error server mailslot name Global\WinAgentCtl_4424_7656_9 is in use, retry...

2025-06-06 07:35:07.641 [ctl:4424] [cmk_agent_ctl::mailslot_transport][WARN] Error server mailslot name Global\WinAgentCtl_4424_7656_10 is in use, retry...

2025-06-06 07:35:07.672 [ctl:4424] [cmk_agent_ctl::mailslot_transport][WARN] Error server mailslot name Global\WinAgentCtl_4424_7656_11 is in use, retry...

2025-06-06 07:35:07.703 [srv 276] Request is '::ffff:10.0.xx.xx'

2025-06-06 07:35:07.704 [srv 276] [Err ] Invalid request '::ffff:10.0.xx.xx'

2025-06-06 07:35:07.704 [srv 276] [Err ] Invalid request '::ffff:10.0.xx.xx'

2025-06-06 07:35:07.735 [ctl:4424] [cmk_agent_ctl::modes::pull][DEBUG] processed task!

Hi,
we have some windows hosts where agent connection gets lost repeatedly.
restarting the checkmk service is solving the issue for a day or two, then the issue happens again. The error above is form checkmk log at this time when connection is lost. any idea what happens here?
Thanks

2

Hi Cob,
maybe this is still an open problem for you. If so, I may have a solution, as I ran into this problem myself and had to contact the Checkmk Support:

When updating the agent from 2.1 to 2.2 or higher, the inter-process-communication between the agent controller and the agent intself has changed from TCP/IP to mailslot, s. Werk Werk #14360: Controller communicates with Windows agent using mailslot

If this causes problems, you can manually downgrade again to TCP/IP communication by editing your checkmk.user.yml. For this, under the system section there is a commented controller section, remove the # in front of it and under this you can change agent_channel from “mailslot” to “localhost:28250” as described in the Werk above:

image
image1070×294 13 KB

After, you still need to restart the Checkmk Service once, so the new config is processed.

Hope this helps!

Cheers,
Leon

3

unfortunately on 2.4p15 there’s no controller section in the checkmk.user.yml on my windows host nor any mention of “mailslot” in that file.

4

This section is only not inside the “demo” config file. You get all options if you do a “check_mk_agent.exe showconfig”.

There you will see a section.

system:
  enabled: yes
  controller:
    run: true
    detect_proxy: no
    validate_api_cert: no
    check: yes
    force_legacy: no
    agent_channel: mailslot
    local_only: yes
    on_crash: ignore
  firewall:
    mode: configure
    port: auto

With your current options.