Error message: I’ve downloaded the .deb package from Setup>Agents>Linux, Solaris, AIX files and I’ve installed in my Ubuntu 22.04 server. I can then see it runs under systemd but the cmk-agent-ctl-daemon.service only listens on IPv6.
tcp6 0 0 :::6556 :::* LISTEN 872492/cmk-agent-ct
I’ve checked with tcpdump and the server packets are indeed reaching the target host.
The fact that you only see “tcp6” in the output does not mean that it is not listening on v4. By default, a v6 socket listens to both v4 and v6. I’ve checked my netstat -tnlp output, and I see a number of processes only appearing in the “tcp6” section, but they all work fine using v4 (sshd, apache, mysql).
To troubleshoot,
first make sure you get valid output if you execute check_mk_agent on the host directly
then, still on the host, try nc 127.0.0.1 6556 or telnet 127.0.0.1 6556
Hi,
thanks! Of all the test I’ve done, this one was missing: telnet 127.0.0.1 6556
It works, hence the agent is doing its job. But tcpdump shows the server packets are reaching the host, but nothing is provided back by the host. Is it possible the agent only accepts requests from the same network?
Could it be a firewall rule? If there’s a DROP rule (vs REJECT), you won’t see response packets in tcpdump. So make sure you don’t drop tcp/6556 traffic coming from your monitoring host.
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