How to Flush Dns Cache In Linux ?
If the DNS information of a website has changed, then the information stored in a computer's DNS cache will have to be updated as well, or else the user will encounter problems when trying to access the website.
This can be achieved by flushing or refreshing the DNS cache. Through this, the old and outdated information of a web address will be removed from the computer's DNS cache, and the updated DNS information will be stored in its place.
How to fix corrupted DNS cache in 
- In many builds of Linux the nscd daemon is used to manage the client DNS cache. For builds that use this method, restarting the nscd daemon is the primary means to flush DNS cache.
- Enter sudo /etc/init.d/nscd restart and press the enter or return key.
- Once nscd restarts the DNS will be flushed. Alternatively, you can enter "service nscd restart"
Note: Ubuntu does not cache DNS per default. 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" and flush the dns as described above.