In ubuntu if you want to flush DNS cache you need to restart nscd daemon Install nscd using the following command sudo aptitude install nscd Flush DNS Cache in Ubuntu Using the following commands
(Install nscd using the following command)
sudo aptitude install nscd
Flush DNS Cache in Ubuntu Using the following command
sudo /etc/init.d/nscd restart
The equivalent of this no Windows is ipconfig /flushdns
References : http://superuser.com/questions/134762/how-to-clear-dns-cache-in-ubuntu