I would do the following...
1) if the server is running UNIX os .
The perl command would be ..
system ("ps -ef | grep username| awk '{ print $2 }' | xargs kill -9") ;
This would kill all the proceeses in your unix server and return to your perl script. Pl note that if you do not want to return to your perl script , use exec command instead of system. Also note that if you are running a database , it would be a better idea to kill your database processes first.
2) If you are running a windows server
The perl command would be ..
system ("taskkill /f /fi username") ;
This would kill all the proceeses of the user forcefully of your windows server and return to your perl script.
Hope This helps