Source : [support.apple.com](http://support.apple.com/kb/HT1343)To use a keyboard shortcut, or key combination, you press a modifier key with a character key. For example, pressing the Command key (the key that has a symbol) and the “c” key at the same time copies whatever is currently selected (text, graphics, and so forth) into the Clipboard. This is also known as the Command-C key combination (or keyboard shortcut). A modifier key is a part of many key combinations. A modifier key alters the way other keystrokes or mouse clicks are interpreted by Mac OS X. Modifier keys include: Command, Control, Option, Shift, Caps Lock, and the fn key (if your keyboard has a fn key).Here are the modifier key symbols you can see in Mac OS X menus:
(Command key) – On some Apple keyboards, this key also has an Apple logo (
)
(Control key)
(Option key) – “Alt” may also appear on this key
(Shift key)
(Caps Lock) – Toggles Caps Lock on or off fn (Function key)
Startup keyboard shortcuts Press the key or key combination until the expected function occurs/appears (for example, hold Option during startup until Startup Manager appears, or Shift until “Safe Boot” appears). Tip : If a startup function doesn’t work and you use a third-party keyboard, connect an Apple keyboard and try again.
Key or key combination
What it does
Option
Display all bootable volumes ([Startup Manager](http://support.apple.com/kb/HT1310))
Shift
Perform a [Safe Boot](http://support.apple.com/kb/HT1564) (start up in [Safe Mode](http://support.apple.com/kb/HT1455))
C
Start from bootable media (DVD, CD, USB thumb drive, and so forth)
T
Start in FireWire target disk mode
N
Start from NetBoot server
X
Force Mac OS X startup (if non-Mac OS X startup volumes are present)
Command-V
Start in Verbose Mode
Command-S
Start in Single User Mode
See also: Startup key combinations for Intel-based Macs.
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