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how to turn off fans in linux

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after running 'sensors-detect' command, kernel modules controlling fan speed should be loaded.

here is an occasion with 'Nuvoton NCT6102D/NCT6104D/NCT6106D Super IO Sensors' detected.

as nct6775 document said:

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#/sys/class/hwmon/hwmon4
pwm[1-7]
    - this file stores PWM duty cycle or DC value (fan speed) in range:
	   0 (lowest speed) to 255 (full)
 
pwm[1-7]_enable
    - this file controls mode of fan/temperature control:
	* 0 Fan control disabled (fans set to maximum speed)
	* 1 Manual mode, write to pwm[0-5] any value 0-255
	* 2 "Thermal Cruise" mode
	* 3 "Fan Speed Cruise" mode
	* 4 "Smart Fan III" mode (NCT6775F only)
	* 5 "Smart Fan IV" mode
...

ps1. if set pwm[1-7]_enable to 0, we will not be able to change it to other value, unless reboot linux.
ps2. I still can't find a common way to turn off fans using ipmitool.

IPMI: Intelligent Platform Management Interface
BMC: Baseboard Management Controller
FRU: Field Replaceable Unit

refer to:
[linux-kernel-src-root]/Documentation/hwmon/nct6775.rst
https://bbs.archlinux.org/viewtopic.php?id=225349