Target display mode connects but only displays desktop background, no files or command lines

I had this issue and figured it out.

Generally, on my late 2009 iMac it ONLY works using a mini dv port to min dv port. You can plug the mini dv port into the mac and a macbook pro's thunderbolt port. Even though the cables on the thunderbolt look the same as the mini dv, they will not work for target monitor mode.

The key if you get the background of your computer is that you need to turn on preferences, open displays, and click ON the "show mirroring options in menu bar when available" option in the lower left corner.

Then go to your display setting tab to "arrangement" and click "mirror displays".

What is currently happening on your monitor when you only see the background is that your active mac is using your iMac as a "second" display. Which means you can drag windows to that screen with your mouse. This might be helpful if you wanted to use two displays at one time! You can even drag your screen around to match the physical position of your computers so when you drag from one screen to the other it is more logical and natural.

To turn the iMac into the same display as your MacBook (or other connected computer) simply click the "Mirror" option in the arrangement panel and now it shows the MacBook's screen.

Your Macbook will now appear on the other screen with the same desktop and dock.

Hi tdmone,

Welcome to the Support Communities! The resource below may help you with the Target Display Mode options for connecting your Macbook and iMac:

Target Display Mode: Frequently Asked Questions (FAQ) - Apple Support
http://support.apple.com/en-us/HT3924

The table below shows iMac computers that support TDM, the required cables, and the port of the computer to which you are connecting the iMac.

iMac Model	Cable Supported	Port on Source Computer
iMac (27-inch Late 2009)	Mini DisplayPort to Mini DisplayPort	Mini DisplayPort or Thunderbolt
iMac (27-inch Mid 2010)	Mini DisplayPort to Mini DisplayPort	Mini DisplayPort or Thunderbolt
iMac (Mid 2011)	Thunderbolt to Thunderbolt	Thunderbolt
iMac (Mid 2012 and later)	Thunderbolt to Thunderbolt	Thunderbolt

Are you connecting via the Thunderbolt ports on both computers?

How do I enable TDM?

• Make sure both computers are turned on and awake.
• Connect a male-to-male Mini DisplayPort or ThunderBolt cable to each computer.
• Press Command-F2 on the keyboard of the iMac being used as a display to enable TDM.
• Note: 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.

Can I use a third-party keyboard or older Apple keyboard to enable TDM?
Some older Apple keyboards and keyboards not made by Apple may not allow Command-F2 to toggle display modes. You should use an aluminum wired or wireless Apple keyboard to toggle TDM on and off.

I hope this information helps ....

- Judy

Many, many thanks JamieP. I was having this issue and you've just sorted it for me. I was just about to chuck the Thunderbolt cable into a drawer in frustration. You're a genius!