Mac OS X Keyboard Shortcuts – Startup Shortcuts invoke a functions during the startup process of the computer. To invoke such functions, you will need to press the key/key combination until the expected function occurs (for example, hold the Option Key during startup until the Startup Manager appears, or hold the Shift key until “Safe Boot” appears).

Apple Logo

FYI: If you are using a third-party keyboard and the function will not load, connect a Genuine Apple OEM keyboard to your machine and try again.

Below are Key/key combinations and what they do:

“Option” key – Display all bootable volumes (Startup Manager)
“Shift” key – Perform Safe Boot (start up in Safe Mode)
“C” key – Start from a bootable disc
“T” key – Start in FireWire target disk mode
“N” key – Start from NetBoot server
“X” key – Force Mac OS X startup (if non-Mac OS X startup volumes are present)
“Command” & “V” keys – Start in Verbose Mode
“Command” & “S” keys – Start in Single User Mode

The Information in this article was found here!