Mac OS X can boot differently than to your default startup disk with the use of modifier keys. When you power a system on, using these keystrokes will send commands to the system to perform the following:
- C – Boot to optical media.
- D (with restore disk in optical slot) – Boot to hardware test mode.
- Command-Option-O-F – Boot to OpenFirmware (if you have open firmware).
- Command-Option-P-R – Reset Parameter RAM.
- Command-Option-P-R (until you hear two tones) – Reset non-volatile RAM.
- Command-Option-N-V – Reset non-volatile RAM (similar to above according to hardware).
- Command-Option-Shift Delete – Bypass the default startup volume and look for another blessed volume.
- Command-Option-T-V – Boot that Quadra you hax0r’d OS X onto to use a TV for a monitor.
- Command-S – Boot to Single User Mode, a command-line only environment, where you will need to mount disks manually, etc.
- Command-V – Boot in Verbose mode, which shows what’s loading in a command-line style environment as it loads. I personally boot my machines in this manner 100% of the time, using the nvram boot-args=”-v” command.
- Eject – Ejects media from the optical slot/tray.
- F12 – Ejects media from the optical slot/tray.
- Mouse button – Ejects media from the optical slot/tray.
- N – Boot to a NetBoot volume.
- Option – Boot to a list of available startup volumes, allowing for startup volume selection.
- Option-N – Boot to a default boot image on a NetBoot volume.
- Shift – Disables nonessential kernel extensions (drivers).
- Shift (if held after the Apple screen is displayed) – Disables user startup items, launch daemons and launch agents.
- Shift (left shift key at the OS progress menu) – Bypass automatic login.
- T – Boot to Target Disk Mode, turning a system into a glorified firewire drive.
- Trackpad button – Ejects media from the optical slot/tray.
- X – Only used with systems that can run OS 9. Forces the system to boot into Mac OS X.
You can also boot the Xserve using startup modifier keys without a keyboard. To do so, boot the system holding down the system identifier button until the top row of lights blinks (blinks like they’re doing the wave). Then let go of the system identifier button and press it noticing the bottom light will change positions. The position number, from right to left performs the following:
- 1 – Boot to an optical drive (similar to using the C modifier)
- 2 – Boot to a NetBoot server (similar to using the N modifier)
- 3 – Startup from the first blessed system found on an internal drive (useful if going from NetBoot or optical)
- 4 – Look for another blessed system on another internal drive (similar to Command-Option-Shift-Delete modifier)
- 5 – Boot to Target Disk Mode (similar to using the T modifier)
- 6 – Rest NVRAM (similar to using Command-Option-N-V modifier)
- 8 – Diagnostic mode
I’m sure there are more modifiers, but these are pretty much the ones I can use. One note about using modifiers is that third party keyboards and KVM switches will often cause modifier keys not to be sent to the Mac computer at the right time and therefore can cause false positives in troubleshooting processes…
