New User need help fixing: [piggyback] Success (but no data found for this host)

[MOTfromH]

**CMK version:**2.3.0
**OS version:**Debian

Error message: [agent] Communication failed: timed outCRIT, [piggyback] Success (but no data found for this host), execution time 5.0 sec

Hi, I’m trying to get knowledge about checkmk and have 2 VMs (Debian 12) running in Proxmox.
on one of them is my webserver which I want to monitor, the other machine is running checkmk, and I can also log in to the GUI of checkmk via the browser.
My webserver has the agent installed, and it is also running (state=up)
unfortunately I have the error:

[agent] Communication failed: timed outCRIT, [piggyback] Success (but no data found for this host), execution time 5.0 sec

Maybe someone can help me pls. I m an trainiee and try to get some praxis.
If you need mor informatons just let me now

greetings

MOT

[Holger (Holger Eudenbach)]

Hi and welcome,

seems like an connection issue, your Checkmk server cant reach your Hostsystem - easy things first:
try ping checks from checkmk → monitored host

ether within the UI, at your Host Configuration page:

which leads to:

or use ping from the Checkmk Server to the Host and vice versa to eliminate asynchronous routing.

[MOTfromH]

At first, thank you, Holger, for your detailed instructions. As a beginner I really appreciate it.

I fallow your steps and committed the changes at the popup sign.
After the nothing changed. Just in case, I checked the agent on the machine.

[Holger (Holger Eudenbach)]

good, icmp works - lets go to Firewall and Ports

Ports - Ports used by Checkmk

(Debian usually has no FW by default but nonetheless, check for UFW or iptables configurations that drop)

Simply use telnet from your checkmk-server to your destination :
Example: (192.168.178.24 is my host, 6556 is the port the agent wants to communicate)

If you dont get a Connected to, the issue is mostly a Firewall/Routing Problem - since you are a trainee, grab your networker/fireworker and let that be explained to you

regards, Holger

[MOTfromH]

Thank you. Of course, I forgot that I already had UFW running. After I open the ports, one status already changed. I immediately included it as a note in my documentation.