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prapi01 Author

Level 1

36 points

Command F2 not working after upgrade to Sierra

I have been using my 27" iMac as the target display for my headless Mac Mini for years ... with the latest being El Capitan. After upgrading to Sierra, I can no longer use Command F2 to switch to target display mode. Pressing Command F2 now just shows a black blank screen. I can toggle it back to iMac display ... so seems that the Command F2 toggle is working but just that the display doesn't show up.

Anyone with this same issue?

iMac, macOS Sierra (10.12), Menubar Clock

Posted on Oct 4, 2016 6:02 PM

Top-ranking reply

blooptybloop

Level 1

4 points

Posted on Oct 13, 2016 8:24 AM

I can confirm this is happening in the new Sierra OS. In order to move forward, I wanted to clear up the troubleshooting suggestions (in bold):

If Command-F2 doesn't work

If your iMac doesn't switch to Target Display Mode when you press Command-F2, check these things:

Make sure the iMac you're trying to use as a display supports Target Display Mode.

Of course it supports it, I, and the user reporting the bug, have used it successfully in the past

Make sure you're pressing Command-F2 on the keyboard that's connected to the iMac you want to use as a display.

I can confirm I am pressing Command-F2 on the display I want to use, and getting a blank black screen

In Keyboard System Preferences, if the checkbox is enabled for Use all F1, F2, etc. keys as standard functions keys, the key combination changes to Command-Fn-F2.

I can confirm I am using the F keys as function keys and not standard. To further illustrate that point, when I hit Command-F2, the display attempts to go into TDM, but just returns a black screen.

Make sure your Mini DisplayPort or Thunderbolt cable is connected to both computers.

I can confirm both cables are thoroughly, securely, and unequivocally attached to both machines.

If you're currently logged in on the iMac you want to use as a display, try logging out to return to the login window. Then press Command-F2 again.

I have logged out, logged in, and reset both machines. Problem still exists.

Some older Apple keyboards and third-party keyboards might not allow Command-F2 to toggle display modes. If this happens, use the keyboard that came with your iMac to toggle Target Display Mode on and off.

I am using an Apple keyboard that is less than a year old.

If your iMac is currently started up in Windows, it won't enter Target Display Mode. Target Display Mode isn't supported in Boot Camp.

I am not starting the mac in Windows. I am booting in Mac OS Sierra on both machines.

Now that we have the copy/paste from the troubleshooting guide out of the way. Is there an actual solution to this apparent bug in Sierra?

View in context

31 replies

Aug 22, 2017 5:52 AM in response to Tim Lynch 1

Sorry for using the *** words. I was struggling last night. My neighbor has a 27" iMac (now I know and he knows that the 4k is not the 5k iMac) connected to his new MBP. I wanted to do the same. At the Apple Store I told the sales guy what I had and he sold me $100 worth of cables (the nuance of the 5k was a small but important detail). Then I got home and it didn't work. We took my laptop and new cables across to my neighbors and it worked fine (again, now we know it is the 5k iMac issue). I will just have to wait until the 5k becomes old enough for apple to deem it target display mode worthy.

Aug 22, 2017 6:34 AM in response to Tim Lynch 1

Tim Lynch 1 wrote:

I will just have to wait until the 5k becomes old enough for apple to deem it target display mode worthy.

Sorry to bust your expectations, but that is not going to happen.

The hardware trickery needed to support the 5K display in these iMacs apparently led Apple to drop support for TDM.

Noone can say if future iMacs will again support this very nice feature (the 2017 models do NOT), but it is almost certain that this will not (cannot?) be retrofitted to existing models that don't support it out of the box.

Aug 22, 2017 7:11 AM in response to Luis Sequeira1

There is a way to get it to work by plugging in the thunderbolt cable between the two computers, and look under the network settings for the "Thunderbolt Bridge" device. Assign each one a private IP different than each other -- even in the "self-assigned IP" space i.e. 169.254.35.10 and 192.168.35.11 - Click on "Advanced" and make sure one of the interfaces shows "Active" From there on the higher-res display, you can VNC over to the other one: Finder -> Go -> "Connect to Server" and enter: vnc://169.254.35.10 or whatever the IP of the other computer is.

Although this isn't Target Display mode

Aug 22, 2017 10:04 AM in response to Tim Lynch 1

Tim Lynch 1 wrote:

There is a way to get it to work by plugging in the thunderbolt cable between the two computers, and look under the network settings for the "Thunderbolt Bridge" device. Assign each one a private IP different than each other -- even in the "self-assigned IP" space i.e. 169.254.35.10 and 192.168.35.11 - Click on "Advanced" and make sure one of the interfaces shows "Active" From there on the higher-res display, you can VNC over to the other one: Finder -> Go -> "Connect to Server" and enter: vnc://169.254.35.10 or whatever the IP of the other computer is.

Although this isn't Target Display mode

You're right this isn't TDM. With TDM you would be using the iMac screen as a second display to your MBP. You would be running software on your MBP and use two screens for it (the iMac would act just like a monitor).

With the process you are describing, you'd just be accessing your iMac remotely - i.e. you'd be using a window in your MBP screen to show you the screen of the iMac, and run applications on the iMac.

Two very different things!

And, to be sure, the latter can be done whether or not you use a Thunderbolt cable, and Thunderbolt Bridge. The two macs could be just connected to the same LAN using Wifi, or even just be connected to the internet half the world apart.

And instead of the general vnc:// you could use Apple's implementation of ScreenSharing.

Aug 28, 2017 10:41 AM in response to Luis Sequeira1

Hello,

This thread seems to be very much alive. I have the same issue with TDM. I have a newer, Late 2015 iMac with a 5K display, which is my main computer, and I have a Late 2013 iMac I would like to use in TDM to extend the desktop of the first one. When I press Cmd-F2 the target iMac flickers for a moment and then the screen goes blank. There no better way to describe this than to share a short video: https://www.dropbox.com/s/cxckk37ebj4seeu/IMG_7157-720.mov?dl=0

I am using a proper Thunderbolt cable between the two computers. I even tried the utility shared above but to no avail. Any clues?

Thank you.

Luis

Aug 28, 2017 11:22 AM in response to Yijingman

After the screen goes blank, can you do command-F2 again to bring the older mac's desktop back? That would suggest that command-F2 is working (in the sense that it turns TDM on and off). The two macs do not seem to negotiate a working display frame size and/or frame rate.

When the display is blank, what do you see in System Preferences->Displays in the 5K iMac? Does the other mac appear? What frame size? Is mirroring turned on? Actually the first thing might be to press command-F1 *on the 5K* to toggle mirroring off.

Tim.T

Level 1

4 points

Oct 10, 2017 4:18 PM in response to prapi01

Adding my experience since this thread is still receiving people who are having TDM problems and it may or may not be Sierra / Mac mini related.

If you're using a Thunderbolt 2 cable, make sure it's plugged in the right way. Sounds silly, but most iMacs that support TDM have rectangular cuts in the back that allow you to insert the Thunderbolt cable either way. It does matter which way you plug it in though - look for the corner grooves on the plug and socket.