fancontrol man page on aLinux

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FANCONTROL(8)							 FANCONTROL(8)

NAME
       fancontrol - automated software based fan speed regulation

SYNOPSIS
       fancontrol [configfile]

DESCRIPTION
       fancontrol is a shell script for use with lm_sensors. It reads its con‐
       figuration from a file, then calculates fan  speeds  from  temperatures
       and sets the corresponding PWM outputs to the computed values.

WARNING
       Please  be  careful  when  using the fan control features of your main‐
       board, in addition to the risk of burning your CPU, at higher  tempera‐
       tures 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  at all.  Also please keep in mind most fans
       aren't designed to be powered by a PWMed voltage.

       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 shut‐
       down call, in case some fan fails, because you probably won't  hear  it
       anymore ;)

CONFIGURATION
       For  easy configuration, there's a script named pwmconfig(8) which lets
       you interactively write your configuration file for fancontrol.	Alter‐
       natively	 you  can  write this file yourself using the information from
       this manpage.

       Since most of you are going to use pwmconfig(8) 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

       DEVPATH
	      Maps  hwmon class devices to physical devices. This lets fancon‐
	      trol check that the configuration file is still up-to-date.

       DEVNAME
	      Records hwmon class device names.	 This  lets  fancontrol	 check
	      that the configuration file is still up-to-date.

       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 Records  the  association	 between a PWM output and a fan input.
	      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).

       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.

       Upon starting, fancontrol will make sure that all referenced devices do
       exist and match what they were at configuration time, and that all ref‐
       erenced sysfs files do exist. If not, it will  quit  immediately,  upon
       the  assumption that the configuration file may be out-of-sync with the
       loaded kernel drivers.

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 temper‐
       ature  changes,	but  only  if the temp is between MINTEMP and MAXTEMP.
       After that, the new values are written to the  PWM  outputs.  Currently
       the speed increases quadratically with rising temperature. This way you
       won't hear your fans most of the time at best.

SEE ALSO
       pwmconfig(8), sensors(1).

AUTHOR
       Marius Reiner <marius.reiner@hdev.de>

lm-sensors 3			September 2009			 FANCONTROL(8)
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