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fancontrol - Unix, Linux Command
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 shouldnt use fancontrol
at all. Also please keep in mind most fans arent designed to be
powered by a PWMed voltage.
In practice it doesnt 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 wont hear it anymore ;)
For easy configuration, theres 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 Im going to describe the various
variables available for changing fancontrols behaviour:
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.
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 to minimum speed.
The temperature over which the fan gets switched to maximum 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,
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 dont want the fan to
If this value isnt defined, it defaults to 0 (stopped fan).
The PWM value to use when the temperature is over MAXTEMP.
If this value isnt defined, it defaults to 255 (full speed).
The configuration file format is a bit strange:
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, /sys/bus/i2c/devices or /sys/class/hwmon
depending on the kernel version) for which the value is valid, equal sign
followed by the value and are separated by a blank. Example:
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. Currently the speed increases
quadratically with rising temperature. This way you wont hear your fans most
of the time at best.
Marius Reiner <email@example.com>