"Magic Keys" during boot

• Cmd-V Verbose startup (text console)
• Cmd-S Single user mode
• T Export internal Disk as firewire device
• C Boot from CD-ROM
• N Boot from Network
• X Switch boot device to MacOS X folder
• Opt Boot device selection
• Cmd-Opt-O-F Enter OpenProm prompt
• Cmd-Opt-P-R Flush OpenProm nvram

"Magic Keys" during operation

• Cmd-Shift-3 Create screenshot, puts a file on the desktop (PDF in MacOS X <= 10.3, PNG in MacOS X >=10.4)
• Cmd-Shift-4 Create screenshot with selection, puts a file on the desktop (PDF in MacOS X <= 10.3, PNG in MacOS X >=10.4), click space to capture a window
• Ctrl-Cmd-Shift-3 Create screenshot, puts it into the clipboard
• Ctrl-Cmd-Shift-4 Create screenshot with selection, puts it into the clipboard, click space to capture a window
• Cmd-Alt-Esc End program
• Shift-Alt-Cmd-Q logoff immediatly
• Ctrl-Cmd-Opt-8 Switch to Black and White (MacOS X <=10.3), inverse screen (MacOS X >=10.4) :)

Settings for boot-args - may be set by command nvram or in the OpenProm prompt:

• -v Verbose boot
• -s Single user
• -x Safe (used by kextd)

Much more magic keys may be found here and here.