“Why does Red Hat tolerate CentOS? The Community ENTerprise
Operating System is an identical binary clone of Red Hat Enterprise
Linux (minus the trademarks), compiled from the source code RPMs
that Red Hat conveniently provides on its FTP site. It is also
completely free, as in beer. CentOS provides no paid support, but
it does track Red Hat updates and patches closely, and usually
makes them available within a few hours or at most a few days of
the upstream provider, which it refers to for legal reasons as ‘a
prominent North American Enterprise Linux vendor.’ Free support for
CentOS can be found in numerous places around the web, and a few
third parties offer modestly priced paid support for those who want
it…”