Basically, I used the native Safari.app web browser to download a third party application and I want to run / open it from the comfort of my bash shell / Terminal.app CLI; despite the following error message:

“<unidentified_thirdparty.app>” can’t be opened because it is from an unidentified 
 developer. Your security preferences allow installation of only apps from the Mac 
 App Store and identified developers. Safari downloaded this file on <today's_date> 
 from <the.inter.net>.

You'll either have to change the settings under System Preferences > Security & Privacy > General > Allow applications downloaded from: to Anywhere or in a Terminal, strip the xattr com.apple.quarantine attribute from the downloaded file(s).

xattr -dr com.apple.quarantine "unidentified_thirdparty.app"
  • I was aware of the GUI method. The next part looks spot-on though. What exactly does the com.apple.quarantine (attribute) argument refer to? – voices Sep 8 '15 at 2:21
  • @tjt263, Sorry I didn't see your comment until now... All filesystem objects have attributes, e.g. information you'd see in the output of the ls -l file command. Filesystem objects also have extended attributes of which com.apple.quarantine is one that is assigned to objects downloaded from the Internet by OS X to help prevent arbitrary execution and thus one level of protecting the system. Using ls -lR@ file or xattr −lr file will show extended attribute information the latter of which will output more extensive information. See man xattr for more information. – user3439894 Jan 31 '16 at 14:17
  • Wow. That's interesting. I did not know about that. Do other Operating Systems have something like this in place? – voices Jan 31 '16 at 18:21
  • You can also use either right-click (aka ctrl-click) and choose "Open", to allow executing just that app. – Hawken Rives May 1 '16 at 1:19
  • 1
    @HawkenRives, Yes it does as it's a global setting not the actual running or opening of the file as the right-click on the file does. Using xattr portion of my answer cover the command line and Terminal. – user3439894 May 1 '16 at 1:32

Enter this in the Terminal under a administrator account: sudo spctl --master-disable

  • This turns off Gatekeeper completely. And it is not an answer to the question. – 639d0991 Sep 1 '17 at 7:47

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