How to flush / clean DNS in ubuntu?

DNS servers convert a domain name (such as example.com) into an IP address (in this case 123.123.123.123). The mapping of names to numbers can change from time to time. Your computer holds a record of DNS entries to save looking them up every time. This is your DNS cache. You can delete those records (flush the cache) any time you like. If a website has recently moved servers, you might see the old website for a while. Flushing your DNS cache might help.

Run these commands to flush your dns cache:

• sudo /etc/init.d/dns-clean restart
• sudo /etc/init.d/networking force-reload
• sudo /etc/init.d/nscd restart
• sudo service network-manager restart