[newbie] radutmp question

Hi all, I have encountered a problem with radutmp. The information of my environment is a vpn service and auth with freeradius 1.1.7. The problem happened as below: 1. start up the radiusd 2. user "abc" connect to vpn, and I can use radwho to see "abc" user 3. shutdown radiusd 4. user disconnect from vpn server (radiusd not start yet) 5. start up radiusd, and radwho still shows "abc" is connected Is there any way to solve this problem? any suggestion is extremely welcomed. Thank you. :) Regards, clyang