How to stop display from turning off when I disconnect a Screen Sharing client

Run this command in the terminal to fix the external screen going blank on VNC disconnect. Works with Sierra OS.

sudo defaults write /Library/Preferences/com.apple.RemoteManagement RestoreMachineState -bool NO 

More context from jabenninghoff on GitHub:

In newer versions of macOS, screen sharing will automatically re-lock the screen when you disconnect if it was locked when you first connected.

Under System Preferences > Sharing, use “Remote Management” instead of “Screen Sharing”, as shown here:

As far as I can tell, everything else works the same but the screen no longer turns off when you disconnect a Screen Sharing connection.

edited to add: this is under 10.11.3

To be clear - the top-rated solution here alone from colo2100cent does not solve the problem if you're connecting to a MacBook with the lid closed (tested using a mid 2011 MacBook Air running Sierra - VNC disconnect required opening the lid and a physical button press to wake it up), but works fine if you're using a desktop based Mac like a Mac mini or an iMac. A display must be connected externally for this to work on a MacBook, but this is wasteful if it's being stored in a closet as a server or otherwise not being physically accessed.

What solved the problem for me was executing the command in colo2100cent's answer:

sudo defaults write /Library/Preferences/com.apple.RemoteManagement RestoreMachineState -bool NO 

while also having a headless ghost display connected to the miniDP port, purchased for about 10 bucks. It tricks your MacBook into thinking there's a monitor connected at all times but does not require a monitor. Works like a charm - no more sleeping after VNC disconnect.

I also have this issue (2012 Mac running El Capitan 10.11.5). I did not have this issue on my 2007 Mac Mini running 10.6.8 with a similar configuration (except using DVI instead of HDMI). When I close Mac screensharing or TouchPad on iOS, or switch iOS apps or lock the phone, the Mac Mini turns off external video.

The workaround I've found is: Hit pause / play on the Apple Remote (the physical infrared remote — not an app) after starting the video, before closing screensharing. Then you should be able to close screensharing and the screen will stay on. I've also done this with the Apple bluetooth mouse and it works as well.

You can also accomplish this by waking the Mac Mini with the remote before initiating screensharing, if you remember. Annoying though since it will often open and start playing iTunes.

The Mac just seems to need some input from a physical device (mouse or remote) after waking to prevent it putting the screen back to sleep.

Going to try the Remote Management checkbox also to see if that helps.

I solved this by restarting the Mac with the display (the TV) already ON.

If starting the Mac with the display off, either using Remote Management or Screen Sharing will result in the display turning off after disconnecting the VNC client.

I know this is a four year old question, but I think I may have finally found a foolproof solution.

The issue is that if it can't detect a display in any capacity it will put it to sleep, the commands don't work anymore(?), etc. Well here is how you create a display without any costly dongles. BetterDisplay, allows you to create virtual displays for free, and at pretty much any resolution. Once the virtual display has been created the Mac will always think it is on and disconnecting from a VNC session will not put the computer to sleep.

Now I am certain I have entered colo2100cent's command into my terminal, I am not sure if it also is required. But so far BetterDisplay has solved the issue.

I am using an old MacBook Pro that has a disconnected damaged display with the lid closed.