When trying to install Yosemite to a fresh hard drive a couple of weeks ago, I realized my knowledge of OS X startup key combinations was very lacking. I did a little research, and found the chart displayed below from Apple’s Support pages (To see the original document, click here). All the OS X startup key combinations and their uses can be viewed.
Note: The OS X startup key combinations are entered AFTER starting the computer. Keep holding key(s) until the mode or process you want starts.
|Start up in Safe Mode.
|Start up to Startup Manager.
|Start up from a bootable CD, DVD, or USB thumb drive (such as OS X install media).
|Start up to either Apple Hardware Test or Apple Diagnostics, depending on which Mac you’re using.
|Start up to either Apple Hardware Test or Apple Diagnostics over the Internet.
|Start up from a compatible NetBoot server.
|Start up from a NetBoot server using the default boot image.
|Start up from OS X Recovery.
|Start up from OS X Recovery over the Internet.
|Reset NVRAM. Release the keys after you hear the startup sound again.
|Start up in single-user mode.
|Start up in target disk mode.
|Start up from an OS X startup volume when the Mac would otherwise start up from a non-OS X startup volume.
|Start up in verbose mode.
|Eject (⏏), F12, mouse button, or trackpad button
|Eject removable media, such as an optical disc.