Host not shown as "down" in dashboard

Troubleshooting
1

hello,

we had an accidental outage of one of our VMs (forget to set autostart, so it did not boot on pve host reboot)

what could be the reason that it’s not shown in main dashboard as being down ?

i’m out of ideas

these are the events from friday:

Friday, 2025-08-08
Time Event State info Summary
![](https://monitor/mysite/check_mk/themes/facelift/images/icon_alert_notify_result.png "Final notification result") 2025-08-08 14:00:19 HOST NOTIFICATION RESULT EXIT_CODE (SUCCESS) {"id":"xvHTuysknfp8","time":1754654419,"expires":1754697619,"event":"message","topic":"checkmk","title":": gitlab ( - 172.20.54.20)","message":"HOST PROBLEM\n CRITICAL - 172.20.54.20: rta nan, lost 100%\n **Acknowledged by $SERVICEACKAUTHOR$**: $SERVICEACKCOMMENT$\\n2025-08-08 14:00:18 Site: mysite","priority":4,"tags":["x"],"actions":[{"id":"sxqsdjAvjF","action":"view","label":"Go to host","clear":true,"url":[![](https://monitor/mysite/check_mk/themes/facelift/images/icon_link.png)](https://monitor/mysite/check_mk/index.py?start_url=view.py?view_name%3Dhoststatus%26host%3Dgitlab%26site%3Dmysite)}]}
![](https://monitor/mysite/check_mk/themes/facelift/images/icon_alert_notify.png "User notification") 2025-08-08 14:00:19 HOST NOTIFICATION NOTIFY (DOWN) CRITICAL - 172.20.54.20: rta nan, lost 100%
![](https://monitor/mysite/check_mk/themes/facelift/images/icon_alert_cmk_notify.png "Core produced a notification") 2025-08-08 14:00:18 HOST NOTIFICATION NOTIFY (DOWN) CRITICAL - 172.20.54.20: rta nan, lost 100%
![](https://monitor/mysite/check_mk/themes/facelift/images/icon_alert_down.png "Host alert") 2025-08-08 14:00:18 HOST ALERT HARD (DOWN) CRITICAL - 172.20.54.20: rta nan, lost 100%
2

Hi, this depends on how you monitor the VM. Do you have an host object for the VM? Is there an agent installed? If not, you will probably only have a service below the vCenter showing the VM as powered off, which is by default a warning.

3

yes, sure i have a host object and the agent is also installed and working. that’s why i wondered

4

Things to check: Is the host ip manual configured and correct? If not, does DNS gives the right ip for the hostname? Is the host check command used icmp as default or is anything special configured? Is the ip pingable while the host is down (maybe some other network component does answer the ping)?

5

yes, all correct and no icmp response when host down

6

What is the Host check command for this server? Udo asked, but I missed it the first time reading their reply and I don’t see you answer it. It’s a key answer to have.

7

i did not change this from default settings, so how do i know what’s the host check command?

there is only one docker rule in Host monitoring rules → Host check command which matches label cmk/docker_object:container

8

You can see the current value of that host’s Host Check Command from the effective parameters page:

It sounds like it will likely be Smart Ping. I’ve had some customers with applicaiton aware firewalls that “freak out” Smart Ping, both in always showing it down and always showing it up. You might consider trying a different method like traditional ping (make a rule for this host changing it to ping) for this specific host.

9

thank you

it’s “PING (active check with ICMP echo request)”

we do not use application aware firewall

10

Something is responding to CheckMK then when it pings the down host. Maybe change it to status of the CheckMK Agent service.

11

ok, will have a look. had no other events of hosts not showing down on outage, so i keep an eye on this if this happens again