Step 1 – Open the Terminal.app

Either start typing Terminal in the Spotlight search, or goto Applications > Utilities > Terminal.

Step 2 – Open the host file

Open the hosts file by typing the following in the Terminal window:

sudo nano /private/etc/hosts

Type your user password when prompted.

Step 3 – Edit the hosts file

The hosts file contains some comments (lines starting with the # symbol), as well as some default hostname mappings (e.g. 127.0.0.1 – local host). Simply append your new mappings underneath the default ones.

Step 4 – Save the hosts file

When done editing the hosts file, press Ctrl O to save the file.

Press Enter on the filename prompt, and

Ctrl X to exit the editor.

Step 5 – Flush the DNS cache

You can use a simple Terminal command to flush the DNS cache, and have your host file changes take immediate effect. Using the open Terminal window, then the following command:

dscacheutil -flushcache

Your new mappings should now take effect.