The FAQ says to use radiusd -X> debug.txt for debug.
I get the following: The program 'radiusd' can be found in the following packages: * radiusd-livingston * xtradius * yardradius Is there another way to launch debug mode in version 2.1? - List info/subscribe/unsubscribe? See http://www.freeradius.org/list/users.html