CentOS 7 contains the FreeRADIUS service version 3.x, which is a major version upgrade from version 2.x on CentOS 6. 

The configuration of the FreeRADIUS service version 3.x is not compatible with version 2.x. There are no automated mechanisms to convert a FreeRADIUS 2.x configuration into a FreeRADIUS 3.x configuration, therefore the conversion must be performed manually by an experienced administrator.
 
The user is advised to install the default FreeRADIUS configuration and make incremental changes while testing each minor alteration. Placing the FreeRADIUS configuration files located in the /etc/raddb/ directory under version control is recommended. Using a source code management (SCM) tool, such as Git or Apache Subversion, enables the user to track changes over time.

Available resources for performing the upgrade include the following:

* Files located in the /usr/share/doc/freeradius*/ directories. Many of these documents are installed by the freeradius-doc subpackage. It is recommended that you install this package.

* The FreeRADIUS man pages, especially unlang(5), and radiusd.conf(5). To see a list of available manpages, run the "man -k radius" command.

* The in-line comments located within the configuration files in the /etc/raddb/ directory. This is where the majority of the FreeRADIUS documentation can be found, and it is of vital importance to read the contents of the configuration files.

* The upstream website [link:http://freeradius.org] and especially the wiki located at [link:wiki.freeradius.org]

* The FreeRADIUS users mailing list available at: [link:http://lists.freeradius.org/mailman/listinfo/freeradius-users]

* Further information at: [link:http://freeradius.org/version3.html] and [link:https://github.com/FreeRADIUS/freeradius-server/blob/v3.0.x/raddb/README.rst]