Here we go again, this worked pre-Yosemite. Now it seems this trick no longer works. After following these steps again the screen on my Macbook Pro now turns on after logging in and opening the clam shell.
Anyone figure out/know a way to turn off the screen on the Macbook Pro with external monitors plugged in? (yes, closing the clam shell–but I'm referring to keeping the clam shell open with the display turned off)
http://gizmodo.com/5938452/a-trick-to-make-using-an-external-monitor-with-your-m acbook-way-better
To execute in Terminal:
sudo nvram boot-args="iog=0x0"
To undo in Terminal:
sudo nvram -d boot-args
Once you type it into terminal I believe you need to enter your password. I then restart my machine. Now the TRICK is to either restart your machine with the lid already closed (hit restart then slam the lid!) OR turn the machine on for the first time (then quickly slam the lid!) once you are past the login screen you can open the lid.
MacBook Pro (Retina, 13-inch, Late 2013), OS X Mavericks (10.9.5)
This solved my question Solvedby kkwan77 on Nov 3, 2014 11:00 PM
Found the solution here: http://apple.stackexchange.com/questions/152203/osx-10-10-yosmite-turn-off-macbo ok-pros-display-while-connect-to-external-moni
In terminal:
Enable: sudo nvram boot-args="niog=1"
To undo: sudo nvram -d boot-args
This works brilliantly!
Steps I use:
1) After putting in the terminal command, reboot and close the lid immediately
2) Keep the lid closed during boot up and once logged in, open the lid
3) The MacBook Pro's screen is off
See the answer in context