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).
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 came from Mac keyboard shortcuts!