, ,

Too geeky? Nah.  I needed to flush or empty the DNS cache on my iMac. DNS means Domain Name System, it is the internet’s tool that maps a human friendly URL such as dagnygromer.wordpress.com to a numeric IP address like The DNS is a distributed system where many domain name registrars maintain these mappings. I needed to change the web host that one of the domains I own maps to, so I logged into my domain account at 1and1.com and made the change.  When I went to the URL, it still went to the old web host. The domain change takes some time to work its way through the distributed DNS so I waited a while – it can take from a few minutes to a few days. Gary was able to get to the new web host OK, I was not. The problem was the out of date domain mapping was being cached by OS X. This is normal and speeds things up, but I had outdated info in my DNS cache so I needed to flush or empty it which forces my computer to get new DNS information from the internet.

Long story I know. Anyway to flush or empty the DNS cache on OS X Mavericks open the terminal application and type or copy and paste in the following line. Then press return or enter.

dscacheutil -flushcache; sudo killall -HUP mDNSResponder

You’ll be asked to enter an administrative password. sudo means “run this command as a system administrator”.

DNS info comes from specialized servers. To see how your mac accesses the DNS system:  Run System Preferences (click the Apply icon at the top left of your screen for a menu to get to this) then click on Network, then Advanced, then the DNS tab and you will see a list of IP addresses. Each is a DNS server, you generally have a few of these listed. If one is busy or not available OS X tries another one. Don’t alter this list unless you are confident in what you are doing.