This directory (and version of CentOS) is deprecated. For normal users,
you should use /6/ and not /6.6/ in your path. Please see this FAQ
concerning the CentOS release scheme:

https://wiki.centos.org/FAQ/General

If you know what you are doing, and absolutely want to remain at the 6.6
level, go to http://vault.centos.org/ for packages.

Please keep in mind that 6.0, 6.1, 6.2, 6.3, 6.4 , 6.5 and 6.6 no longer gets any updates, nor
any security fix's.