Below I am going to outline how to install Nagios 3.5.0 on CentOS 6.4 from source. I'm assuming that you are starting from a clean minimal install of CentOS
Ok first lets get the needed packages
Now lets get nagios and it's plugins, at this time the link below was the most up to date, but you can verify this by omitting the data after the last trailing slash.
Now unpack and lets start with Nagios fist:
Now lets get those plugins working.
Now check your base build, if you get any errors, you will need to fix them first
Now start it up
Now, here is where I want to strangle most other websites... DO NOT disable selinux! It's dumb to not just properly configure it! Below I will help you to authorize Nagios in SElinux.
If you find that you are getting blocked cmd in nagios, run the following to fix it.
That should do it, to add hosts, you need to edit the files in /usr/local/nagios/etc/objects/
If this was helpful, please let others know in the comments below!