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Gatekeeper is a new security scheme built into Mountain Lion. The idea of it is pretty simple. In the past when we downloaded applications for our Macs, we had to rely on the source for those applications to be trustworthy, that the applications didn't contain any malicious elements that might make our Macs perform poorly or, worse yet, share our personal data with the bad guys. With Mountain Lion, Apple adds an extra layer of security that helps to ensure that the source for your software is unfailingly reliable.
That security measure is called Gatekeeper, and it works this way. So we're going to go into System Preferences. I'll go into the Security & Privacy system preference, and we'll look in the General tab. In this gray area here, you see Allow applications downloaded from, and you have three options. I want to configure those options so I have to click the lock icon and enter my administrator's password, and now it's unlocked. Now as you see, there are three settings here.
The first, which is unchecked by default, is a Mac App Store. This means if you select this option, you'll be able to download applications but open them only if they're from the Mac App Store. You can download applications from anywhere, but if you try to open them and they're not from the Mac App Store, you'll be told that you can't open them and that you'll have to change your Gatekeeper options in order to open what you want. The second option, which is on by default, and this is Mac App Store and identified developers. Again, you can download applications from the Mac App Store or from anywhere else you like, but if you try to open them and they are not from an identified developer or from the Mac App Store, you'll be told that you can't open them.
So what does this mean? What does it take to become an identified developer? These developers have registered with Apple. This registration helps Apple to determine whether you're a trustworthy developer. Now they don't go through each and every one of your applications, but rather you've registered with them, Apple knows who you are if you're one of those developers, and if something goes a miss, they can revoke your permission to run applications using Gatekeeper. So this adds an extra layer of security. And finally, the Anywhere option means that your Mac will work as it has under previous versions of Mac OS X. You can download and open software from anywhere you like.
If you manage to download something harmful, well, that's your fault for enabling this option. If you're viewing this course shortly after the release of Mountain Lion, which was July of 2012, it's possible that some completely legitimate developers haven't completed the registration process to earn their Apple certificate. If however, we are well into 2013 or later, any Mac developer worth his or her salt will have registered. Under that circumstance, there would be very little reason for you to choose the Anywhere option. Note that there's a fairly simple way to get around Gatekeeper.
So for example, if you have the second option enabled, which is enabled by default, you download something from somewhere else and you don't want to come back here and change your configuration. I'll show you how to do that. I am going to open the Applications folder, and I'll find this program called OnyX. It's a terrific application for configuring little preferences on your Mac. So at this point I'm allowed to open applications that I've downloaded from the Mac App Store or from certified third-party developers. I double-click on OnyX to try to open it, and it tells me that I can't, because it's from an unidentified developer.
So at this stage as I record this, the people who developed OnyX have not yet registered with Apple. So what can I do? Well, of course I can go back to Security & Privacy and change my preferences, or I'll click this OK to dismiss it. Now I hold down the Ctrl key and click on it and I choose Open. When I do that you see a different kind of dialog box. It says, OnyX is from an unidentified developer. Are you sure you want to open it? Because I held down the Ctrl key and chose Open, now you see that I have this Open option.
I click on that, I'll agree to the license agreement, and I'll click Cancel on these various things. Finally, I've opened the application. So this is a shortcut for getting around Gatekeeper limitations. Not something you should have to do very often, but if this pops up, now you know how to get around it. And that's pretty much the long and short of Gatekeeper. It's not an option that you should have to configure very often, but should you be prevented from using perfectly respectable applications that you've downloaded, you now know how to get around Gatekeeper's restrictions.
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