I'm only able to find up to version 5 on CentOS.com:http://www.centos.org/docs/Even though CentOS 6 was released back in mid-2011..
Where are the CentOS 6.4 documents?
centos;documentation
I've been using the RHEL6 docs instead. They're essentially the same.https://access.redhat.com/site/documentation/Red_Hat_Enterprise_Linux/Here are the CentOS 6 Release Notes, if you're interested. The highlight the above link there as well.