mulitipule connections

[Ski Mountain]

   Hello, I have searched quite a bit.  I am looking for a answer on the best way to disable mulitipule logins by the same user.

I have been reading
http://freeradius.org/radiusd/doc/Simultaneous-Use

One problem is I get a error when I try to run
 radwho
radwho: Error reading /var/log/freeradius/sradutmp: No such file or directory


This checkrad.pl scrpt I can not find it anywhere on my ubuntu 10.04 server.  Where would if find a copy.  

I do have a 

radutmp file.  Should there be entries in it when no one is connected? 

So is the only way,to run snmp on the server, or has that way outdated now? 

Thanks for the help