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I have to admit, the research that I've done suggests that it is not possible to do this (and that it is more complicated than originally thought). The Raspberry Pi outputs HDMI, and iMacs (at least those from mid-2010) do not accept HDMI inputs -- they only accept Mini DisplayPort inputs, which typically come from other Apple products.

As far as I'm aware, HDMI and Mini DisplayPort are incompatible formats, and the only way to get from HDMI to DisplayPort is to use a bulky, expensive converter. You cannot do this with a passive adapter; however, if you want to go in the other direction (e.g. use the iMac as an output device by connecting a DisplayPort on your iMac to a HDMI television) then this is possible, quite cheaply.

Basically, the iMac can be a HDMI output device, but not a HDMI input device.

Is this the case? And if so, does anyone know a workaround (that doesn't involve spending £150 on a Kanex XD)?

Sputnik
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    Not sure if this belongs on the Ask Different (Apple) stack exchange or not – Alexander Aug 04 '12 at 00:45
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    @XAleXOwnZX This is on-topic for [raspberrypi.se] and so we aren't going to migrate it out. Sorry. =P –  Aug 04 '12 at 00:53
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    Sure it's on topic, (it has RPi involved) but a much better answer could be obtained from people who know about the true nature of this question: target display mode on iMacs. – Alexander Aug 04 '12 at 01:03
  • How about using a USB TV Capture device? I cannot see any other easy way – Piotr Kula Aug 04 '12 at 09:35

2 Answers2

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You can start a GUI on the host machine, in this case your Mac, over SSH. This is only two steps, three if you count setup.

Before you do anything you need to install and configure SSH on your machine. You need to be able to ssh into the Raspberry Pi via your Mac.

  1. Now you have to SSH into the Raspberry Pi. This can be accomplished like so.

    $ ssh -X username@hostname

    NOTE You need to use the -X flag. This enables X11 port forwarding allowing you to view the GUI on your Mac. Make sure that you use the uppercase version and not -x as the lowercase version disables X11 port forwarding.

  2. Now you need to use exec to start your window manager. For example, in order to start LXDE you would run the following command.

    $ exec startlxde

What should happen is that you should see the Raspberry Pi's screen on your Mac. Now you should be able to control the Raspberry Pi via your Mac and see what is on your Raspberry Pi's screen.

References

  1. Get RaspberryPi display on iMac
  • While this does get a display from the Pi on the Mac, it's not directly displaying the video signal from the board on the iMac's monitor. – scruss Aug 04 '12 at 02:00
  • No, but this does still accomplish the job and is much cheaper than buying a HDMI to DisplayPort converter. –  Aug 04 '12 at 02:01
  • Thanks for this, Bryan. I think I am going to go for a cheap HD TV instead as I'll need a display anyway to set up an IP address on the R-Pi. But it's nice to know that it can be done. – Sputnik Aug 04 '12 at 15:14
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    @Spütnik: You don't need a display to set the IP address. Just edit /etc/interfaces/network on the SD-card from another computer. http://www.penguintutor.com/blog/viewblog.php?blog=6306 – Kleist Aug 04 '12 at 22:22
  • I can confirm that this works! :D However, for more in-depth instructions (including for Windows and other OS's) see these two fantastic pages on the Wiki: http://elinux.org/RPi_A_Method_for_ssh_blind_login and http://elinux.org/RPi_Wheezy_VNC. – Sputnik Aug 08 '12 at 16:37
  • I don't get how you can ssh into Pi or from Pi if you don't even know if it started successfully or not (as you don't have a monitor) – themihai Nov 04 '14 at 11:44
  • I'm just adding onto @user46 's answer... You can definitely SSH into the machine. But in order to do so you may need to use the Raspberry Pi's default hostname (since you probably don't know the IP) raspberrypi. ssh -X pi@raspberrypi Alternatively if you want to find IP address I would suggest logging into your router and viewing the connected devices. – Myg0t Apr 12 '16 at 21:55
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According to Apple, you need a converter

Summary With Target Display mode, you can use your iMac (27-inch, Mid 2010) or iMac (27-inch, Late 2009) with Mac OS X as an external display. Connect any computer or other device with a Mini DisplayPort to your 27-inch iMac using a Mini DisplayPort to Mini DisplayPort cable or using a converter that converts other electrical, video, and audio protocols from another source device to Mini DisplayPort compliant signals. (Cables and converters available separately.)

More details here

Connecting a Video Source to Your iMac

The 27-inch iMac has a bi-directional Mini DisplayPort that can be used to drive a second monitor. The same Mini DisplayPort can be used as a video input that allows your iMac to serve as a monitor for an external video source. All you need is the proper adapter.

The Mini DisplayPort in the 27-inch iMac can only receive DisplayPort-compatible video and audio. It can’t receive analog video or audio sources, such as those from a VGA connector, but it’s possible to use adapters for digital DVI, HDMI, etc.

...

John La Rooy
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