How to change your Host files
Your Mac’s hosts file is a small, but important text document that has the ability to map hostnames to specified IP addresses. Although the modern Internet uses a variety of public and private DNS servers to map IP addresses, the hosts file is a handy way to override those DNS servers, allowing you to manually point a website address to a desired IP address, or block access to a site altogether by pointing to an unused or internal IP address. Here’s how to edit the Mac hosts file on OS X.
There are two primary ways to edit the hosts file in Mac OS X. The first is by using TextEdit, since the hosts file is merely a simple plain text document. However, you can’t open the file directly, since it resides in a protected area of the file system. Instead, we need to copy the file to an unprotected location, like the Desktop, edit it, and then copy it back.
To find the hosts file, open Finder and, in Finder’s menu bar, select Go > Go to Folder. In the box, type the following location and press Return.
/private/etc/hosts
A new Finder window will open and your Mac’s hosts file will be selected. Click and drag it out of the Finder window and drop it on your desktop. This will let us freely edit the file.
To open it, simply double-click and it will display the file’s contents in TextEdit (or the text editor of your choice). By default, the hosts file is relatively simple. It contains a number of lines of descriptive text which are “commented out” with the pound or number sign (#). For each line, any text after the pound sign is ignored by the computer, making it a good way to add notes and descriptions to your files. It also contains default IP values for localhost and broadcasthost. To edit the file, you’ll add your own lines after broadcasthost.
A popular use for an edited hosts file is to block access to specific websites. In our example, we’ll pretend that the computer we’re using is a work system, and we want to prevent employees from accessing Facebook (because we’re mean). To do this, type the IP address you wish to assign followed by a hostname. In our case, we want to block Facebook so we’ll map www.facebook.com to 0.0.0.0 which, as an invalid IP address, will result in an error. Now, whenever anyone using the Mac tries to go to www.facebook.com, their Web browser will fail to load the page.
Alternatively, you can enter the IP address of a valid site instead of 0.0.0.0, which will result in users attempting to access Facebook being directed to the site of your choosing. To determine a website’s IP address, you can “ping” the site via Terminal. Simply open Terminal and type the following command, replacing “www.website.com” with the website of your choice:
ping www.website.com
Make note of the IP address that’s returned and use it in your Mac hosts file mapping. For example, The New York Times website at www.nytimes.com returns an IP address of 170.149.172.130. If we map that to Facebook in our hosts file, any time someone using the Mac tries to go to Facebook, they’ll see the The New York Times load instead.
You can add as many entries to the hosts file as you wish by entering new mappings on each line. Once you’ve made your desired changes to the hosts file, save it in its current location on the Desktop. Then, drag and drop the hosts file from your Desktop back to its original location at /private/etc. If you’ve closed the Finder window pointing to this directory, simply use the Finder > Go > Go to Folder command, discussed above, to reopen it.
When you drop the hosts file back in its original location, OS X will ask you what to do about the unmodified hosts file that’s already there. Choose “Replace” and then enter your administrative user password to authenticate the transfer.
With the modified hosts file now in place, fire up your Web browser to test the changes. In most cases, the new mapping should work immediately, but if you’re not seeing the correct behavior, you may need to flush your DNS cache. For OS X Lion and OS X Mountain Lion, open Terminal and use the following command. Note that you’ll need to enter your admin password to execute it:
sudo killall -HUP mDNSResponder
For OS X Mavericks, use this command instead:
dscacheutil -flushcache; sudo killall -HUP mDNSResponder
The steps in the previous section are easy enough, but if you want to avoid copying the hosts file you can edit it directly in Terminal using the UNIX Nano Text Editor, which is built in to OS X.
To get started, launch Terminal, type the following command, and press Return. As with all sudo commands, you’ll need to also enter your admin password to execute it:
sudo nano /private/etc/hosts
You’ll now see the hosts file open in the Nano editor. To navigate and edit the file, use the arrow keys on your keyboard.
Just as we did with the TextEdit method, above, we can add, edit, or remove hostname mappings at will. Because we launched Nano using sudo, any changes will be authenticated and saved directly to the original hosts file, without the need to copy it outside of its home directory.
When you’re done making changes, press Control-X to exit the editor, Y to save, and Return to overwrite the existing hosts file. As we mentioned earlier, make sure to flush your DNS cache if you notice that your new mappings aren’t working properly.
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