Quiet the runaway fan on an Apple iMac running Linux — a "Macs Fan Control" replacement, with an optional Omarchy bar widget.
Status: v0.1.0, early. Working and in daily use on one machine (
iMac12,2). Other models should work but are untested — see Compatibility.
The 2010–2011 iMacs have three fans: ODD, HDD, CPU. When the original
Apple hard drive is replaced with a third-party SSD, the SMC loses that drive's
temperature signal and pins the HDD fan at its maximum RPM — permanently,
no matter how cool the machine is. macOS users reach for Macs Fan Control.
On Linux there was no tidy answer; this is one.
imac-fan is a small root daemon that takes only that one fan onto a quiet,
temperature-aware curve (regulating on the hotter of CPU package and GPU
diode). The CPU and ODD fans stay under the firmware's control. A CLI and
an Omarchy bar widget switch modes without root.
quiet hold at the fan's minimum
auto follow the curve (default) — silent when cool, ramps if the machine heats up
max full speed
off hand the fan back to the firmware
git clone https://github.com/mudiam/imac-fan
cd imac-fan
sudo daemon/install.sh
imac-fan statusNeeds Python 3 (stdlib only), systemd, and the applesmc module (loaded
automatically on Apple hardware). No other dependencies.
omarchy plugin add https://github.com/mudiam/imac-fan --enable
sudo ~/.config/omarchy/plugins/imac-fan/daemon/install.shomarchy plugin add clones the repo to ~/.config/omarchy/plugins/imac-fan/
and drops the widget on the bar; the second line installs the daemon it talks
to.
The widget shows the fan RPM; left cycles quiet/auto/max, right forces full speed, middle sends a status notification. It turns to a fan-alert glyph if the fan is pinned near max with no daemon running.
imac-fan status # RPM, mode, regulating temperature
imac-fan quiet|auto|max|off
imac-fan set 1600 # fixed custom RPM
imac-fan cycle # quiet -> auto -> max -> quiet
/etc/imac-fan/config, then sudo systemctl restart imac-fan:
| key | default | meaning |
|---|---|---|
FAN |
2 |
applesmc fan to control (2 = HDD on the 27" 2011) |
QUIET_RPM |
1100 |
RPM for quiet mode (this fan's firmware minimum) |
CURVE |
55:1100 68:1900 78:3200 85:4800 |
degC:RPM points for auto, linearly interpolated |
CRITICAL_TEMP |
92 |
force max RPM at/above this, in any mode |
RESTORE_ON_EXIT |
1 |
hand the fan back to firmware when the daemon stops |
DEFAULT_MODE |
auto |
mode before the CLI/widget has set one |
Which fan is yours? sensors | grep -i fan or
for f in /sys/devices/platform/applesmc.*/fan?_label; do echo "$f $(cat $f)"; done.
Pick the one that is stuck near its max; set FAN to its number.
Only the daemon writes to /sys (that needs root); systemd starts it at boot.
The CLI and widget write one keyword to /var/lib/imac-fan/mode, which the
daemon polls and sanitises — it reduces any content to
quiet|auto|max|off|fixed:<int> and clamps the RPM to the fan's own limits, so
a bogus or hostile value can do nothing worse than select the auto curve.
That file is root:wheel, group-writable, so switching modes needs no
password. If wheel doesn't exist the daemon falls back to world-writable.
Tested on a mid-2011 27" iMac (iMac12,2, Intel HD 3000 + Radeon HD 6970M).
Should work on any Mac the applesmc driver supports; FAN and CURVE are
the only model-specific settings. Not for Apple Silicon.
Running it on another model? Please open an
issue with your Mac model and
the output of sensors and
for f in /sys/devices/platform/applesmc.*/fan?_label; do echo "$f $(cat $f)"; done
— it helps build a known-good FAN/CURVE table.
mbpfan and
macfanctld are general Apple fan daemons.
imac-fan is narrower on purpose: it fixes the one SSD-swap failure mode,
leaves the firmware in charge of everything else, and integrates with the
Omarchy bar.
sudo daemon/uninstall.sh
omarchy plugin remove imac-fan # if the widget was installedMIT