Breezed is a small daemon to control the speed of the fan,
   depending on the current temperature of the computer. I have tested
   it only on a Thinkpad X61s.

 * INSTALLATION

   You can install it simply by running as root

     ./install.sh

   and de-install it with

     ./remove.sh

   You must have a configuration file in /etc/breezed.conf. Only one
   is currently provided in the archive, and it corresponds to the
   settings _I_ picked for _my_ Lenovo X61s.

   I have no idea if these settings are safe on this laptop (I guess
   so, since I have been using them for a few months now and it works
   perfectly), and I suspect they are not safe for another laptop.

 * ALGORITHM

   Breezed scans the temperatures every 5s and sets the fan speed
   according to a series of thresholds.

   Unfortunately, if the fan speed is set directly according to these
   temperature thresholds, it creates oscillations: The fan goes up,
   temperature goes down, hence fan goes down, temperature goes up,
   etc.

   To mitigate such phenomenons, the daemon waits at least 30s after
   the last change before reducing the fan speed, and the actual
   thresholds to decrease the fan speed are two degrees below the
   provided thresholds, which are used when increasing the fan
   speed. This creates a stability area of two degrees, which seems to
   be enough. Please let me know if you have problem with the
   resulting overall behavior.

 * ARGUMENTS

   The breezed executable can read a configuration file (which is
   /etc/breezed.conf by default, but that you can specify with
   --configuration-file <file>) or get the various parameters on the
   command line.

   The thermal files can be specified either with the --thermal-files
   options on the command line or the thermal_files keyword in the
   configuration file. The provided value should be a comma-separated
   list of filenames. When it want to pool the temperature, the daemon
   will read those files and compute the maximum integer value they
   contains.

   The fan file can be specified with either --fan-file or the
   fan_file keyword. The specified file will be used by the daemon to
   control the fan speed by writing "level n" into it.

   The temperature thresholds can be specified either with the
   --temperature-thresholds argument, or with the
   temperature_thresholds keyword in the configuration file. The
   provided value should be a comma separated list of integers. The
   first one is actually ignored and forced to -1. Each value states
   which temperature should trigger the given level.

   For instance, my X61s has 8 fan levels, from 0 to 7. The thresholds
   I picked are -1,52,54,56,58,60,62,64. Hence, when the temperature
   reaches 52C, the fan is set to level 1, when it reached 54C it is
   set to level 2, etc. The maximum speed level 7 is chosen for any
   temperature equal or greater than 64C. As said above, the
   temperature to decrease the speed has to be two degrees below the
   provided thresholds. Hence, the temperature of my X61s has to go
   down to 50C (52C - 2) for the fan to switch off. Also, the daemon
   waits at least 30s before reducing the speed of the fan.

 * NOTES

   I wrote this daemon for my personal usage on a X61s, and using it
   may damage your hardware.

   On Thinkpads you have to allow the module thinkpad_acpi to set the
   fan speed, which is not allowed by default in Debian. To do so, you
   have to have a file /etc/modprobe.d/thinkpad_acpi.modprobe
   containing

   ---------------------------- snip snip -------------------------------
   options thinkpad_acpi fan_control=1
   ---------------------------- snip snip -------------------------------

--
Francois Fleuret (francois@fleuret.org)
December 2008