linux-c6 and linux-c7

I've recently installed FreeBSD as a desktop, and I'm attempting to get Linux compatibility working, in the ports tree there is both linux-c6 and linux-c7 as well as linux_base-c6, c7.

What is the difference between these ports? Is it necessary to install all of them or should I install just one?

linux_base-c6 is based on CentOS6, c7 is CentOS7. The linux_base-* is the bare minimum, linux-* is a more complete installation and includes linux_base-* plus a few other bits and pieces.