What is nmi_watchdog related to Linux ?

ABOUT NMI

Short for non-maskable interrupt, NMI is the highest priority interrupt capable of interrupting all
software and non-vital hardware devices. The NMI is not commonly used and usually only used to verify if
a serious error has occurred or stop all operations because of a failure. For example, when you press
Ctrl+Alt+Del when the computer freezes or stops responding an NMI is sent to the CPU.

ABOUT watchdog

A watchdog in computer terms is something, usually hardware-based, that monitors a complex system for
“normal” behaviour and if it fails, performs a system reset to hopefully recover normal operation.

ABOUT nmi_watchdog

Enables/Disables the NMI watchdog on x86 systems. When the value is non-zero the NMI watchdog is enabled
and will continuously test all online cpus to determine whether or not they are still functioning
properly. Currently, passing "nmi_watchdog=" parameter at boot time is required for this function to work.

If LAPIC NMI watchdog method is in use (nmi_watchdog=2 kernel parameter), the NMI watchdog shares
registers with oprofile. By disabling the NMI watchdog, oprofile may have more registers to
utilize.

TYPICAL SHELL SESSION RELATED
[bash]
root>pwd
/proc/sys/kernel
root>cat nmi_watchdog
1
root>cat /proc/sys/kernel/nmi_watchdog
1
root>
[/bash]

A PART OF A TYPICAL COMMAND IS SHOWN
[bash]
$apt-cache show freeipmi-bmc-watchdog
Package: freeipmi-bmc-watchdog
Source: freeipmi
Version: 1.5.7-2.1
Installed-Size: 152
Maintainer: Debian FreeIPMI Maintainers <pkg-freeipmi-devel@lists.alioth.debian.org>
Architecture: amd64
Depends: libc6 (>= 2.14), libfreeipmi17 (>= 1.1.5), libgcrypt20 (>= 1.7.0), freeipmi-common (= 1.5.7-2.1), freeipmi-tools
Pre-Depends: dpkg (>= 1.15.7.2~)
Description-en: GNU implementation of the IPMI protocol – BMC watchdog
FreeIPMI is a collection of Intelligent Platform Management IPMI
system software. It provides in-band and out-of-band software and a
development library conforming to the Intelligent Platform Management
Interface (IPMI v1.5 and v2.0) standards.
.
This package contains a watchdog daemon for hardware BMC watchdogs.
Description-md5: de829f061dc1ffe58f7abb1eed647eb0
Homepage: http://www.gnu.org/software/freeipmi/
Tag: implemented-in::c, role::program
Section: admin
Priority: optional
Filename: pool/main/f/freeipmi/freeipmi-bmc-watchdog_1.5.7-2.1_amd64.deb
Size: 43524
MD5sum: 88b812dd810689b59fd0d35063e1af49
SHA256: 763d3bd2f55d804487e1ab9b77fecd5087e826089c5083c10736982d093dafd9
[/bash]

LINKS
https://www.kernel.org/doc/Documentation/watchdog/watchdog-api.txt
http://www.sat.dundee.ac.uk/~psc/watchdog/watchdog-background.html
https://www.computerhope.com/jargon/n/nmi.htm
https://www.gnu.org/software/freeipmi/index.html