CheckMK || Linux Agent Default Port // Host is registered for TLS but not using it

[DerMeldos]

Error message:
[agent] Host is registered for TLS but not using it, Got no information from host

A possible reason is that a different program is already using the default port 6556.
This can be checked with "ss"

root@NETBOX0702:~# ss -tulpn | grep 6556
tcp   LISTEN 0      4096               *:6556            *:*    users:(("systemd",pid=1,fd=54))

To fix this we need to change the port of the interfering program or alter the port for the checkmk agent.

To change the checkmk agent port:

you must create (or edit) the file "/var/lib/cmk-agent/cmk-agent-ctl.toml" on the monitored host and add this line (The file doesn’t exist by default.):

pull_port = 16556

After that, do a systemctl restart cmk-agent-ctl-daemon.service.

Create a rule for the Agent within the CheckMK Webview:
Setup > Agents > Access to agents > TCP port for connection to Checkmk agent

Example rule: