A common way to "block" a website (eg, to eliminate it as a distraction) is to edit
/etc/hosts and point the domain to the loopback address. Eg:
# Stop goofing off 127.0.0.1 youtube.com
On Mavericks, I find that changes like this are seemingly ignored by the OS; after editing the file (with sudo) and saving, the site that should be blocked still loads.
I've tried resetting my DNS cache as follows:
dscacheutil -flushcache sudo killall -HUP mDNSResponder
But the site still loads.
How can I get OSX Mavericks to notice a change to