Generating a Non-Maskable Interrupt
Interrupt the kernel on a target Mac and attach a remote debugger to it.
Overview
Debugging many types of kernel-level problems requires a second Mac computer to run the debugger. On your target Mac, configure the debug boot arg with the options you need to support non-maskable interrupts (NMIs). The DB_NMI (0x4) flag causes the kernel on the target Mac to wait for a debuger to attach when an NMI occurs; add other flags as needed. After an NMI occurs, use the debugger on your second Mac to examine the system and diagnose any issues.
For information about how to configure your Mac to debug kernel processes, sign in and download the Kernel Debug Kit from https://developer.apple.com/download/more/.
Trigger a Non-Maskable Interrupt Manually
The following table lists the keys you press to trigger an NMI on different types of Mac.
Mac | Key presses |
|---|---|
Apple silicon | Command (Left) + Command (Right) + Delete |
Intel-based Mac (with Apple T2 Security Chip) | Command (Left) + Command (Right) + Delete |
Intel-based Mac (without Apple T2 Security Chip) | Command (Left) + Command (Right) + Power Button |
For information about which Intel-based Mac computers have the Apple T2 Security Chip, see About the Apple T2 Security Chip.
Configure a One-Button NMI
To trigger an NMI manually using only the target Mac’s power button, add the DB_NMI_BTN_ENA (0x8000) flag to the debug boot arg. Using only the power button makes it possible to trigger an NMI early in the Mac’s boot sequence. For example, you can trigger an NMI before the system loads the USB keyboard driver, or trigger one on systems with no keyboard at all. Combine this flag with the DB_NMI flag and set the boot args on your target Mac as shown in the following example:
sudo nvram boot-args="<current settings> debug=0x8004"When you set one or more debug flags, the target Mac retains the designated capabilities until you remove the flags using the nvram tool. To remove all boot args, run the nvram tool with the -d option, as shown in the following example:
sudo nvram -d boot-args