Automatic CPU Fan Control

EDIT: Designed and tested on ArchLinuxARM, reported as working on Ubuntu.

You need to be superuser to access gpio pins, sudo will not work.
sudo su
The Geekbox fan (fan power plug) is controlled by GPIO3_B3 (gpio107). You can control this pin from a terminal by enabling it for output.
echo 107 > /sys/class/gpio/export
echo out > /sys/class/gpio/gpio107/direction
Turn the fan on with:echo 1 > /sys/class/gpio/gpio107/value
Turn the fan off with:echo 0 > /sys/class/gpio/gpio107/value


Let's make a bash script that checks the CPU temperature and turns the fan on or off automatically.

CPU temp can be found bycat /sys/rockchip_thermal/tempThe reply is not a simple numeric value so we have to manipulate it in our code.

Enter this script with your favorite editor and save it as /usr/bin/fancontrold
#!/bin/bash

FAN_ON_TEMP="50"    # Desired operating temp range
FAN_OFF_TEMP="45"   # Off is always less than on

if [ ! -d /sys/class/gpio/gpio107 ];
   then
   echo 107 > /sys/class/gpio/export;
   echo out > /sys/class/gpio/gpio107/direction;
fi

echo 1 > /sys/class/gpio/gpio107/value;

while [ 1 ]; do
 read CPUTEMP < /sys/rockchip_thermal/temp
 IFS=':' read -r -a temp <<< "$CPUTEMP"
 if [ "${temp[1]}" -gt "$FAN_ON_TEMP" ]; then echo 1 > /sys/class/gpio/gpio107/value; fi
 if [ "${temp[1]}" -lt "$FAN_OFF_TEMP" ]; then echo 0 > /sys/class/gpio/gpio107/value; fi
 sleep 15
done

The temperature settings I have here are conservative. The fan should cycle when the CPUs have a light load, and remain on under heavier loads. A small hysteresis prevents the fan from rapidly cycling.

Set permissions on this file with
chown root:root /usr/bin/fancontrold
chmod 755 /usr/bin/fancontrold
You can execute this script from the commandline, or better yet, let's create a systemd service to execute the script automatically on boot.

With an editor, create this file and save as /lib/systemd/system/cpufan.service
[Unit]
Description=CPU Cooling Fan Service
Requires=basic.target

[Service]
Type=simple
User=root
ExecStart=/usr/bin/fancontrold
ExecStop=/usr/bin/pkill -u root fancontrold
Restart=on-error

[Install]
WantedBy=multi-user.target

Set permissionschown root:root /lib/systemd/system/cpufan.service
chmod 644 /lib/systemd/system/cpufan.service
Tell systemd you want this service to run on boot withsystemctl enable cpufan.service
If you don't want to wait, you can start it now withsystemctl start cpufan.service

Tried and tested on ArchlinuxARM.