how do I install the stock centos repositories?

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http://unix.stackexchange.com – I have a situation where the stock repo files that should exist in /etc/yum.repos.d/ (like centos-base.repo) are not present. I need to get them installed. I am sure this is simple, but after hours of searching, it seems I am not googling it correctly. Basically I have a server with custom repos that are useless to me. I need epel, and epel needs centos-base.repo. I also need postgres repo. Thanks- (HowTos)