What is NMI?
NMI Overview
A Non-Maskable Interrupt (NMI) is a hardware interrupt that cannot be ignored by the processor. These types of interrupts are usually reserved for very important tasks and to report hardware errors to the processor.
Depending on the make and model of the system, you may be able to deliberately send an NMI to the CPUs. By sending an NMI to the processor, it is forced to switch CPU context to the registered non-maskable interrupt handler. The interrupt cannot be ignored (masked). The operating system can handle the NMI based on prior configuration.
An intentionally triggered NMI can help to highlight:
Whether a CPU is capable of servicing interrupts.
Whether an operating system process or task is continuously looping on the CPU.
(Reference: https://kb.vmware.com/s/article/1014767)
Background:
NMI Button The non-maskable interrupt button header is located on pins 19 and 20 of JF1. Refer to the table on the right for pin definitions.
(Reference:
However, with
universal rails instead of the supplied supermicro
here doesnt seem to be a way to trigger it externally (like a pinhole or something)
Solution:
IPMI tool can be leveraged to trigger a NMI.
If the IPMI tool Is not install it can alternatively be executed from Shelladmin.
ipmitool -H <ip address/hostname> -U ADMIN -P <admin pass> <command>
Command is - <chassis power diag>
The core file is found in /var/core of the esxi host.
Use cases:
When ESXi host is hung, not responsive but pingable and able to be SSH. In scenarios like these a hard reset will trigger a HA event and host will be operational. However, the root cause might not be determined. An NMI will help in generating a coredump which will help VMware vendor to perform analysis to determine the root case of host hung reason.