Creating hosts file entries allows you to create DNS aliases which can be very handy for web development. If your on a Mac, you will notice that it has the /etc/hosts file just like other unix os's.

One problem I kept running into however was that OS X was caching my host entries. So if I added a line like this:

192.168.0.80 dev.example.com

And then I changed it to this:

127.0.0.1 dev.example.com

The dev.example.com host will still resolve to the old IP address.

Flushing the DNS Cache on Mac

If you are running Mac OSX Leopard (10.5) or greater, you use the dscacheutil command to flush the dns cache, eg:

dscacheutil -flushcache

If you are using an earlier version of Mac OSX, for example 10.4, then you need to use the lookupd command:

lookupd -flushcache