Introduction

fan-ctrl is a little daemon that controls the speed of one or more system or CPU fans. It does so by monitoring temperature inputs and selecting a fan speed from an array of available speeds based on a set of temperature thresholds.

Why thresholds instead of smooth speed control? Because my CPU fan has a few resonance frequencies which make it "sing". Unfortunately, one of those resonance frequencies is right at the idle operating temperature when using the BIOS automatic control, or lmsensors' fancontrol without tweaking. On top of that, it's less annoying to have the fan change speed in steps using a hysteresis of a few degrees to minimize the chance of the fan speed jumping up and down, possibly going through resonance points again and again.

A word of caution: If this program screws up, the parameters are set incorrectly or the OS crashes badly, the fan speed might be too low and the CPU might overheat. Modern CPUs should be able to deal with this, starting to throttle and eventually resetting the system or going offline, but there might still be damage.

You have been warned...

License

fan-ctrl is not public domain software. It's copyrighted by myself, Christian Mueller, according to the terms of the GNU General Public License (GPL). Please see the file LICENSE for additional information.

Project Location

The latest version of fan-ctrl can be found here.

This project is hosted on SourceForge:

Installation

There's no release tar file at this point. Please download the source code with CVS using the following commands:

cvs -d:pserver:anonymous@fan-ctrl.cvs.sourceforge.net:/cvsroot/fan-ctrl login

Just hit Return when it asks for a password

cvs -z3 -d:pserver:anonymous@fan-ctrl.cvs.sourceforge.net:/cvsroot/fan-ctrl co -P fan-ctrl

The compile process is rather simple, thus there's no automake or configure script at this point, just a makefile for Linux.

In order to compile the program, type "make".
In order to install the program into /usr/local/sbin, type "make install"
In order to install the program on a Debian system into /usr/sbin, including scripts to automatically start fan-ctrl at system boot time, type "make install-debian". Once completed, please run "update-rc.d fan-ctrl defaults" and check /etc/default/fan-ctrl for configuration information. The default settings will *not* start fan-ctrl automatically.

Running fan-ctrl

In order to run fan-ctrl, you first have to figure out the best parameters for the fan(s) you're trying to control. I'm assuming a CPU fan for the rest of this README, namely a Thermaltake TR2 R1, and a Gigabyte GA-MA790GP-DS4H mainboard which has the CPU fan on pwm1 and the CPU temperature on temp2_input.

Steps to get the required parameters:

Get lmsensors working. fan-ctrl is based on lmsensors and probably won't work with ACPI-based sensor readings and fan controls. In order to set up lmsensors, check out the documentation at
http://www.lm-sensors.org/

Once everything is working, you should be able to run "sensors" and get both the CPU temperature and the CPU fan speed. Try running
```
  while true; do false; done
```
in a terminal window to generate some CPU load to see the CPU temperature and/or the CPU fan speed going up (and down once you press Ctrl+C)
Once lmsensors is working and you know the CPU temperature input (tempX_input) and the CPU fan control output (pwmX), play around with various fan speed settings while watching the CPU temperature and the fan speed:
- Run "watch sensors" in a terminal to get an updated display of the current fan speeds, temperature readings, etc.
- change into /sys/bus/i2c/devices/<your device>
- echo 1 >pwmX_enable
  (X being the fan control port)
- echo 255 >pwmX
  (the fan should speed up now, running at max RPM)
- now it's time to match temperature readings with fan speeds and load. A good way to start would be to take an idle system and reduce the fan speed until the temperature goes up. Idle systems should not run at more than 40-50°C CPU temperature, preferrably less if this can be achieved with a reasonably low fan speed. Reducing the fan speed can be done as follows (as root):
```
echo 180 >pwm1 (assuming "1" is your fan)
```
  If the temperature goes up beyond 60°C, quickly type "echo 255 >pwm1" to prevent damage. Or pull the plug ;)
- It's also a good idea to test whether the fan will actually start to run with the desired idle speed when it's currently stopped. In order to do this, set the fan speed to 0, wait until sensors reports 0 RPM, then set the fan speed back to the idle speed determined above. If it doesn't start, increase the speed until it does and use this value for the minumum speed at idle temperature.
- Once the best idle fan speed has been determined, interpolate the temperature and fan speed at idle to, say, 60°C at full load. In other words, make sure that the fan runs at full speed when reaching 60°C
- Determine steps (e.g. by setting fan speeds manually to find out where resonance frequencies are cousing trouble) and distribute those steps evenly across the minimum and maximum fan speed; 5-10°C per step would be a good starting point.
when done, construct the command line for fan-ctrl like in this example:
```
    fan-ctrl -p /sys/bus/i2c/devices/9191-0228 -f pwm1 -t temp2_input \
	     -s 0:142,40:176,50:196,55:226,60:255 -h 5
    
```
- base path is /sys/bus/i2c/devices/9191-0228
- fan to be controlled is pwm1
- temperature input is read from temp2_input
- fan speeds are set as follows:
```
	 0 - 39°C  ->  142
	40 - 49°C  ->  176
	50 - 54°C  ->  196
	55 - 59°C  ->  224
	60°C+      ->  255 (max)
      
```
- hysteresis is 5°C, i.e. fan won't slow down until temperature dropped 5°C below threshold

run fan-ctrl as described above and keep an eye on the temperatures and fan speeds in the terminal running "watch sensors". If anything fails, kill fan-ctrl and it will restore maximum RPM for all controlled fans. If this fails, pull the plug.
- adding the flag "-d" will prevent fan-ctrl from becoming a daemon and will print temperature readings and fan speed settings to stdout; furthermore, you can simply hit Ctrl+C to stop fan-ctrl and restore full fan speeds.
- once everything works as desired, you can start fan-ctrl automatically during system startup (see below).

Startup

On a Debian system, after editing /etc/default/fan-ctrl and enabling it, use "/etc/init.d/fan-ctrl start" to run fan-ctrl.

Command line options

-d	Print debugging messages to stdout; fan-ctrl will not deamonize and run in the foreground
-n <interval>	Update interval. This defines the interval used by fan-ctrl to update the fan speed. Default is 10s
-p <base_path>	Base path for fan control output and temperature input contol files. Can be set multiple times and affects only the following -f and -t options. Default is an empty string.
-f <pwm_out>	The PWM (Pulse Width Modulation) control file used to set the fan speed. This option defines a new fan to be controlled. In other words, multiple "-f" options allow defining multiple fans to be controlled.
-f <temp_in>	The temperature input file to be used for controlling the fan specified with "-f"
-s <temp:speed,...>	An array of temperature/speed values to be used by fan-ctrl. Temperature and speed are separated by a colon (:), pairs are seperated by commas (,)
-h <hysteresis>	The hysteresis to be used when temperatures are falling. In other words, don't reduce the fan speed until the temperature has dropped "-h" degrees below the threshold for the fan speed. This prevents fan speeds from jumping up and down until the temperature and fan speed finally stabilize.

Example:

  fan-ctrl -p /sys/bus/i2c/devices/9191-0228 -f pwm1 -t temp2_input \
           -s 0:142,40:176,50:196,55:226,60:255 -h 5

Stopping fan-ctrl

Use "killall fan-ctrl" to stop fan-ctrl. On a Debian system, use

/etc/init.d/fan-ctrl stop

Suspend and Hibernate

It's a good idea to stop fan-ctrl when suspending or hibernating (add a 1s sleep to the suspend/hibernate script to give fan-ctrl a chance to ramp up the fans) and re-enabling fan-ctrl once the system resumes. This way, the fan speed will be set to maximum before going into suspend/hibernate and fan-ctrl will only resume its work after the resume operation has completed successfully.

If anything fails during those operations, the fans will be either at maximum speed or BIOS-controlled.