Make the agent work with Home Assistant OS

[dnlldl]

General information

The current Linux agent doesn't work with Home Assistant OS (HAOS: https://www.home-assistant.io/installation/linux) because /bin/bash is in fact a redirection to /bin/sh. The openwrt agent is compatible with HAOS but doesn't provide as much information. It is notably missing the systemd agent information.

Proposed changes

To make the Linux agent work with sh, the <<< operators need to be replaced and the bash for loop syntax needs to be adapted as it is not compatible.

I am not sure what is the best approach to this as I don't have a variety of systems to test it on; it might break the agent on other systems although I didn't encounter any issue in my lab with my other Linux distros. A separate agent might be ideal but I admit we're entering a very niche OS that would not be worth supporting a completely total different agent. In that regard, it would probably be better for me to submit a new agent specifically for HAOS to the Checkmk Exchange, but I still wanted to leave a trace on the git and have your thoughts on the matter.

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