If you are using /check_yum you might face the following error…
YUM output signature is larger than current known format, please make sure you have upgraded to the latest version of this plugin. If the problem persists, please contact the author for a fix
nano /etc/nagios/nrpe.cfg
set the correct command to check_yum
command[check_yum]=/usr/lib64/nagios/plugins/check_yum --all-updates
and then restart nrpe
/bin/systemctl restart nrpe.service