Upgrade to Sierra, can't open .dmg

if you want to downgrade your OS to accommodate WebEx you will need to erase the current drive entirely or install a previous OS X variant to another boot drive or partition.

See this article, behavior of the gatekeeper has changed slightly in Sierra from that of previous OS X variants.

OS X: About Gatekeeper - Apple Support

In OS 10.12 now prevents "Anywhere" to appear unless it is "triggered" directly after an attempted install from software with an unknown or no developer license. "Anywhere" will appear only when the user tries to launch software with from an unknown developer the first time:

Gatekeeper OS X 10.11

Gatekeeper OS X 10.12

Functionality to allow software from "Anywhere" is no longer a selectable change for the system.

See these articles If you can’t download an item from the web using Safari on Mac - Apple Support

Download items from the web using Safari on Mac - Apple Support

Right click on .dmg file and click on open , or double click .dmg file and if this is an app it should be dragged and dropped in applications , as .dmg files always occupy hard disk space and should be deleted when the task is completed by restarting the machine and empty the trash .

It's from a well know 3rd party genealogy commercial website: RootsMagic-7-Mac.dmg. However, a weird thing just happened. I have been clicking on it all day with no effect and I just clicked on it now and it opened. I have no idea why it happened this time or what i did.

I'm still a bit new transitioning to MAC after some 30+ years with windows and still don't know why something doesn't work and then it does. But, you're right, I'm glad I got the program installed and I thank you for your quick responses and desire to help those in need.

I know I would be totally lost on Windows so I can feel your pain.

Check out this site that has free videos on using the Mac. They are short so it's easy to find the time for a video or two.

https://macmost.com/video-listMacMost Video Archive By Category – MacMost

The following covers some basics:

Have you tried in the Guest User?

Log out under the Apple in the Menu bar.

Log into Guest

Open Safari in the Dock

Download a file for testing.

Does it open when you double click or Control-Click (Right-click) on the file and select Open?

Same thing happens to me when I try to open a copy of rosetta stone I purchased from Amazon. Was able to get my macbook air to let me download it (seems to be the issue someone had above), but double clicking the DMG and it just sits there...

I have been having this problem for over a month. Surprised Apple hasn't patched this by now. Does anyone have any solutions that don't involve getting lucky double clicking it? I've tried everything suggested in this thread and still no solution.

I also had this issue recently. Realized it would SOMETIMES open randomly. Figured out I needed to do a reset of my mac and allow it to install an update and then BAM - i could open my .dmg.

So when all else fails - try a simple reset of your mac. 🙂

I am having the same problem. I have tried control-click --> open multiple times. It is for RosettaStone.dmg, so a vendor I trust. syspolicyd keeps starting, according to the Activity Monitor, and must be turning down the request. I'm on High Sierra 10.13.3 and there is no option for download from anywhere on the Security and Privacy settings.

I'd really like to install this app!

Found a better answer. I was trying to open the dmg files in the Downloads folder, using the control-click option....

What I didn't realize was it was putting a copy of the dmg file on my desktop. When I double clicked on them, it opened the Security & Privacy settings and gave me the option to "install anyway". Everything worked fine after that.

Hold down the Control key when you click on the .dmg file then select Open. This should give you a window to "allow anyway".

Boot into Safe Mode, Mac OS X: Starting up in Safe Mode, and try opening it from there.