First things first, check the process
# /etc/init.d/nagios status nagios is stopped
Not running? Odd. ok, start it up
# /etc/init.d/nagios start nagios is stopped Configuration validation failed [FAILED]
# /usr/bin/nagios -v /etc/nagios/nagios.cfg Checking... Total Warnings: 0 Total Errors: 0 Things look okay - No serious problems were detected during the pre-flight check
So, I checked the log files and they are all from past dates, including nothing from the last day or so.
# cat /var/log/nagios/nagios.log | perl -pe 's/(\d+)/localtime($1)/e' | less
Nifty perl script there to fix the dates, but it's not mine, just a web snippet.
I was stumped. Then I had a thought, SELinux errors...
# getenforce Enforcing
# setenforce permissive
and give it another shot,
# /etc/init.d/nagios start nagios is stopped Starting nagios: [ OK ]
As they say on Afrotechmods,
A lot of folks disable SELinux in their environments as it can get rather complicated. However, for this issue I was able to dig up this post regarding setting up a new type definition for Nagios, but haven't yet tried it myself.