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Once you ve configured the service and have it running, you should be able to boot your client computers from it by pressing the N modifier key at boot, which instructs a client to attempt a network-based boot.

Mac OS X can boot from sources other than your default internal start-up disk through 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 from optical media. D (with restore disk in optical slot): Boot from hardware test mode. Command-Option-O-F: Boot from OpenFirmware (if you have open

firmware).

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

command-line-like environment as it loads. I boot my machines in this manner 100 percent 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 from a NetBoot volume. Option: Boot from the startup manager, a list of available startup

Option-N: Boot from a default boot image on a NetBoot volume. Shift: Disables nonessential kernel extensions (drivers). Shift (if held after submitting login credentials): Disables user startup

Shift (left shift key at the OS progress menu): Bypass automatic login. T: Boot from Target Disk Mode, turning a system into a glorified FireWire drive (including access to optical drives). Trackpad button: Ejects media from the optical slot/tray. X: Forces the system to boot into Mac OS X (used only with systems that can run OS 9).

You can also boot an Xserve to a NetBoot server, using the start-up modifier keys without a keyboard. To do so, boot the system holding down the system-identifier button until the top row of lights blink in succession, Knight Rider style. At this point, let go of the system identifier button, then press it again, and you ll notice that the bottom light will change positions. The position number, from right to left, indicates the following:

1: Boot from an optical drive (similar to using the C modifier) 2: Boot from 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 CommandOption-Shift-Delete modifier)

5: Boot from Target Disk Mode (similar to using the T modifier) 6: Reset NVRAM (similar to using Command-Option-N-V modifier) 8: Diagnostic mode

Once you ve selected the desired boot option, press and hold the identifier button until all status indicators light sequentially. Release the button, and the system will finish booting. If you want to select the optical drive, you need to press the identifier an additional time once you ve inserted the disk.

You can use the bless command to define boot options in a more granular fashion programmatically. It can define where a Mac OS X computer will boot from. The folder option defines a directory to boot from, while you can use the file option to choose a specific booter file (such as bootx). To boot from a second volume, use the folder option with the path to a volume s /System/Library/CoreServices directory:

The command in this example calls bless with the setBoot option, which tells EFI to use this device as its primary boot device. The nextonly option is particularly helpful, as it allows booting to a device just once, after which it resumes operation from the previous start-up disk. This option has great utility: rebooting to maintenance partitions