fancontrol

FANCONTROL(8)               System Manager's Manual              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).

       AVERAGE
              How  many last temperature readings are used to average the tem-
              perature.  It can be used to smoothen short  temperature  peaks.
              If this value isn't defined, it defaults to 1 (no averaging).

       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. Af-
       ter that, the new values are written to the PWM outputs. Currently  the
       speed  increases  linearly  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)