From LinuxSwords Wiki

control you fan via cmdline

for thinkpad-users

If you run

cat /proc/acpi/ibm/fan

you get the following output:

status:         enabled
speed:          3676
level:          auto
commands:       level <level> (<level> is 0-7, auto, disengaged)
commands:       enable, disable
commands:       watchdog <timeout> (<timeout> is 0 (off), 1-120 (seconds))

If your familiar with such ibm-specific command you know that you can run as root

echo "level 0" > /proc/acpi/ibm/fan

to turn your fan off (don't do it, unless you know what your doing). Also you can bust your fan to full power with:

echo "level 7" > /proc/acpi/ibm/fan

To reset to normal run:

echo "level auto" > /proc/acpi/ibm/fan