Startup key combinations for Macs

Intel-based Macs

Press C during startup	Start up from a bootable CD or DVD, such as the Mac OS X Install disc that came with the computer.
Press D during startup	Start up in Apple Hardware Test (AHT), if the Install DVD 1 is in the computer.
Press Option-Command-P-R	Press until you hear two beeps. Reset NVRAM
Press Option during startup	Starts into Startup Manager, where you can select a Mac OS X volume to start from.
Press N	Make the the first bootable Network volume appear as well.
Press Eject, F12, or hold the mouse (/trackpad) button	Ejects any removable media, such as an optical disc.
Press N during startup	Attempt to start up from a compatible network server (NetBoot).
Press T during startup	Start up in FireWire Target Disk mode.
Press Shift during startup	Start up in Safe Boot mode and temporarily disable login items.
Press Command-V during startup	Start up in Verbose mode.
Press Command-S during startup	Start up in Single-User mode.
Press Option-N during startup	Start from a NetBoot server using the default boot image.

Apple Boot Key Combos

Bypass startup drive and boot from external (or CD)	CMD-OPT-SHIFT-DELETE
Boot from CD (Most late model Apples)	C
Force the internal hard drive to be the boot drive	D
Boot from a specific SCSI ID #.(#=SCSI ID number)	CMD-OPT-SHIFT-DELETE-#
Zap PRAM	CMD-OPT-P-R
Boot into open Firmware	CMD-OPT-O-F
Clear NV RAM. Similar to reset-all in open Firmware	CMD-OPT-N-V
Disable Extensions	SHIFT
Rebuild Desktop	CMD-OPT
Close finder windows.(hold just before finder starts)	OPT
Boot with Virtual Memory off	CMD
Trigger extension manager at boot-up	SPACE
Force Quadra av machines to use TV as a monitor	CMD-OPT-T-V
Boot from ROM (Mac Classic only)	CMD-OPT-X-O
Force PowerBooks to reset the screen	R
Force an AV monitor to be recognized as one	CMD-OPT-A-V
Eject Boot Floppy	Hold Down Mouse Button
Select volume to start from	OPT
Start in Firewire target drive mode	T
Startup in OSX if OS9 and OXS in boot partition	X or CMD-X
Attempt to boot from network server (Hold until Mac Logo appears)	N
Hold down until the 2nd chime, will boot into 9?	CMD-OPT
OSX: Watch the status of the system load	CMD-V
OSX: Enter single-user mode (shell-level mode)	CMD-S

After startup

Bring up dialogue for shutdown/sleep/restart	POWER
Eject a Floppy Disk	CMD-SHIFT-1 or(2) or (0)
Force current app to quit	CMD-OPT-ESC
Unconditionally reboot	CTRL-CMD-POWER
Fast Shutdown	CTRL-CMD-OPT-POWER
Goto the debugger (if MacsBug is installed)	CMD-POWER
Reset Power Manager on PowerBooks	USE THIS LINK
Put late model PowerBooks & Desktops to sleep	CMD-OPT-POWER

Application Specific Keys

Startup key combos to reset the resolution on video boards:

SuperMac (at least some models)	Press & hold OPT
Imagine 128 Card (reset resolution)	N
RasterOps (at least some models)	Press & hold CMD-OPT-SHIFT
Radius (Use cable sense pins to set resolution)	U
Radius (Cycle through available resolutions)	T

Conflict Catcher

Pause Boot	P
Launch CC at Startup	SPACE or CAPS LOCK
Skip remaining extensions	CMD-PERIOD
Reboot cleanly while loading extensions	CMD-R

RAM Doubler

Disable at Startup

~ (Tilde) or ESC

Apple System Installer

Change custom install to clean install

CMD-Shift-K

Claris Emailer

Bypass specified startup connections	Hold CMD at launch
Bring up rebuild options	Hold OPT at launch