Executing the Linux agent over SSH

Owned by Sebastian Kirchmeyer
Last updated: Oct 27, 2023 by Matthew Hierholzer
2 min read

Possible error messages while executing the Linux agent over SSH.

LAST TESTED ON CHECKMK 2.2.0P1

Table of Contents

Problem

When executing the Checkmk agent for Linux via SSH, you might encounter error messages when something is configured properly. Usually, the service Check_MK will notify you about any connection problems that might occur. Below, we will list a couple of these error messages and try to give some pointers as to what might solve your troubles.

screenshot of Services of host myserver. Check_mk service reports Permission denied, please try again later.


Solution

Error Message 01

Agent exited with code 255: Permission denied, please try again.

Possible Cause

The public key in the file authorized_keys on the host might contain an error. This can easily happen when - for example - a line break is somehow inserted in the key, or you omitted a single character, when copying the key to the host.

Possible Solution

Double and triple-check, that the public key on the host you are trying to monitor is 100 % the same as on your Checkmk server.


Error Message 02

Agent exited with code 255: Host key verification failed.CRIT, Got no information from the host, execution time 0.0 sec

Possible Cause

The error message here is clear. The "host key verification failed". But what does this mean? It might just mean that you never introduced your Checkmk server and the host to one another, and hence the key fingerprint is not available in the file _~/.ssh/known_hosts_ on your Checkmk server.

Possible Solution

This one can be resolved easily. Log in to your site and create an SSH connection to your host. SSH should now ask you if you actually want to connect to this machine. You should answer by typing 'yes'. This will add the host to the list of known hosts.