Section: Maintenance Commands (8)
Updated: January 27, 2005
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fancontrol - automated software based fan speed regulation
fancontrol is a shell script 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.
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
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 shutdown call, in case
some fan fails, because you probably won't hear it anymore ;)
For easy configuration, there's a script
named pwmconfig(8) which lets you interactively write your
configuration file for fancontrol. Alternatively 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:
This variable defines at which interval in seconds the main loop of
fancontrol will be executed
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 and a fan.
Then fancontrol can check the fan speed and restart it if it
The temperature below which the fan gets switched off completely.
The temperature over which the fan gets switched to full speed.
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.
The minimum speed at which the fan still spins. Use a safe value here,
If you set up your configuration by hand, be sure to include ALL variables and
use valid values, there's no error handling yet! The file format is a bit
Each variable has its own line. The variable name is followed by an equal sign
and the device=value pairs. These consist of the relative path to the pwm
output (from /proc/sys/dev/sensors/) for which the value is valid, equal sign
followed by the value and are seperated by a blank. Example:
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.
fancontrol first reads its configuration, writes it to arrays and loops its
main function. This function gets the temperatures and fanspeeds from
lm_sensors proc 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. Currently the speed increases
quadratically with rising temperature. This way you won't hear your fans most
of the time at best.
Marius Reiner <firstname.lastname@example.org>
- THE ALGORITHM
- CONFORMING TO
- SEE ALSO
linux.jgfs.net manual pages