Specifications

Programmer’s Switches

Key combinations for programmer’s switches that used the Power button on earlier models now use the Eject

key. Here are the key combinations for the Power Mac G5 computer.

●

Control-Command-Eject: restart immediately (reset)

●

Control-Command-Option-Eject: shut down immediately

●

Control-Eject: display the dialog for shutdown, restart, and sleep

The key combinations are decoded in software and may not be available under some crashed conditions.

NMI without Programmer’s Switch

Current Macintosh computers do not have a programmer’s switch, which allowed users to generate a

non-maskable interrupt (NMI). The paragraphs below describe how to generate an NMI from a remote session

for systems that do not have a physical programmer's switch.

Starting with Mac OS X 10.1.2, the OS will promote and recognize the DB_NMI bit in the “boot-args” property

of the “chosen” node from Open Firmware. When the DB_NMI bit is set, the user can generate a non-maskable

interrupt (NMI) by pressing the system's power button. This replaces the power button’s sleep or wake response.

The system reads the state of the bit at boot time from the boot-args configuration variable. For more

information about the debug flags, please see Inside Mac OS X: Kernel Programming.

To set the DB_NMI bit, enter the following command at the Terminal to display the current debug flag settings.

% nvram boot-args

Add the parameter debug=0x4, as follows.

% sudo nvram boot-args="<current settings> debug=0x4"

After rebooting, press the power button for approximately 1 second to generate an NMI.

Note: If the power button is pressed for more than five seconds, the system will immediately power

off.

The power button will retain this functionality until Mac OS X is restarted without the DB_NMI bit set. To clear

this bit, issue the nvram command omitting debug=0x4 parameter, as follows.

Input and Output Devices

Keyboard