Since it took me days to discover the existence of an in-repo, alternative, let me post it here for people trying to do the same.

I’m used to having Icinga and NRPE monitor Ubuntu and Debian update status with check_apt (in repo: nagios-plugins-basic or monitoring-plugins-basic, depending on OS version). Was trying to do the same for yum based CentOS / RHEL but could only find out of repo check_yum.pl and check_yum.py (by Hari Sekhon, at https://github.com/HariSekhon/nagios-plugins/). Those work fine. However it turns out similar functionality is already available in-repository on at least CentOS 6.8 thru 7.2 and, googling around, likely also on Fedora and RHEL . There is a check_updates in package nagios-plugins-check-updates, which also works fine but might be hard to discover because of the name.