fancontrol - automated software based fan speed regulation

Introduction

fancontrol is a shellscript for use with lm_sensors. It reads its

configuration from a file, then calculates fan speeds from temperatures and

sets the corresponding pwm outputs to the computed values.  It is included in

lm_sensors since version 2.8.0. For easy configuration, there's a script

named pwmconfig which lets you interactively write your configuration file for

fancontrol. Alternatively you can write this file yourself using the

information from the configuration section of this document.

Please be careful when using the fan control features of your mainboard, in

addition to the risk of burning your CPU, at higher temperatures there will be

a higher wearout of your other hardware components, too. So if you plan to use

these components in 50 years, _maybe_ you shouldn't use fancontrol/your

hardware at all.  Also please keep in mind most fans aren't designed to be

powered by a PWMed voltage, for more detailed information on this I recommend

this appnote: http://www.maxim-ic.com/appnotes.cfm/appnote_number/707

In practice it doesn't seem to be a major issue, the fans will get slightly

warmer, just be sure to have a temperature alarm and/or shutdown call, in case

some fan fails, because you probably won't hear it anymore ;)

Configuration

Since most of you are going to use the pwmconfig script, the config

file syntax will be discussed last. First I'm going to describe the various

variables available for changing fancontrol's behaviour:

INTERVAL

	This variable defines at which interval in seconds the main loop of

	fancontrol will be executed

FCTEMPS

	Maps pwm outputs to temperature sensors so fancontrol knows which

	temperature sensors should be used for calculation of new values for

	the corresponding pwm outputs.

FCFANS

	FCFANS records the association between a pwm and a fan.

	Then fancontrol can check the fan speed and restart it if it

	stops unexpectedly.

MINTEMP

	The temperature below which the fan gets switched to minimum speed.

MAXTEMP

	The temperature over which the fan gets switched to maximum speed.

MINSTART

	Sets the minimum speed at which the fan begins spinning. You should

	use a safe value to be sure it works, even when the fan gets old.

MINSTOP

	The minimum speed at which the fan still spins. Use a safe value here,

	too.

MINPWM

	The PWM value to use when the temperature is below MINTEMP.

	Typically, this will be either 0 if it is OK for the fan to plain

	stop, or the same value as MINSTOP if you don't want the fan to

	ever stop.

	If this value isn't defined, it defaults to 0 (stopped fan).

MAXPWM

	The PWM value to use when the temperature is over MAXTEMP.

	If this value isn't defined, it defaults to 255 (full speed).

A graph might help you understand how the different values relate

to each other:

    PWM ^

    255 +

        |

        |

        |                             ,-------------- MAXPWM

        |                           ,'.

        |                         ,'  .

        |                       ,'    .

        |                     ,'      .

        |                   ,'        .

        |                 ,'          .

        |       MINSTOP .'            .

        |               |             .

        |               |             .

        |               |             .

 MINPWM |---------------'             .

        |               .             .

        |               .             .

        |               .             .

      0 +---------------+-------------+---------------->

                     MINTEMP       MAXTEMP            t (degree C)

The configuration file format is a bit strange:

VARIABLE=chip/pwmdev=value chip/pwmdev2=value2 [...]

VARIABLE2=[...]

Each variable has its own line. The variable name is followed by an equal sign

and the device=value pairs. These consist of the path to the pwm output for

which the value is valid, equal sign followed by the value and are separated

by a blank. Path can be absolute or relative (from /sys/bus/i2c/devices or

/sys/class/hwmon depending on the kernel version).

Example:

MINTEMP=hwmon0/device/pwm1=40 hwmon0/device/pwm2=54

You have to play with the temperature values a bit to get happy. For initial

setup I recommend using the pwmconfig script. Small changes can be made by

editing the config file directly following the rules above.

The algorithm

fancontrol first reads its configuration, writes it to arrays and loops its

main function.  This function gets the temperatures and fanspeeds from

kernel driver files and calculates new speeds depending on temperature

changes, but only if the temp is between MINTEMP and MAXTEMP. After that, the

new values are written to the pwm outputs.  The pwm value increases

linearly with rising temperature.

Planned features

rc-scripts for some gnu/linux-distributions

smoother regulation (temp interpolation)

gui for configuration

If you have other wishes or want to contribute something, please let me know:

marius.reiner${AT}hdev.de