Does it matter if we use NRPE behind XINETD or as a standalone app for the upgrade process?
Looks good!
If you're changing from/to xinetd to/from daemon, make sure the old config is removed, and do either make install-inetd or make install-init.
Take a look at the NRPE troubleshooting guide for more details but that message points to that NRPE is not running. https://assets.nagios.com/downloads/nag ... utions.pdf
Verify that the settings in the /etc/xinetd.d/nrpe file didn't get reset and that you restarted xinetd after the upgrade.
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Our install guide instructs you to compile using --enable-command-args, you will need to do that for NRPE v3 (the linux agent script autmatically does it for you).