Catalogue :

sudo cat  var/log/messages | grep 10.20.239.17 | less
sudo cat var/log/messages | grep vpn.log
sudo cat var/log/messages
sudo cat var/log/radius/radius.log

Monitor Live Logs:

sudo tail -f  var/log/messages | grep 10.20.239.17 | less
sudo tail -f var/log/messages | grep vpn.log
sudo tail -f var/log/messages
sudo tail -f /var/log/radius/radius.log