dfan

A lightweight CPU fan controller daemon for Linux. Reads temperature from the k10temp kernel module and drives fan PWM channels through the nct6687 chip, with a configurable curve, live tuning, and clean systemd integration.

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Features

• Five curve shapes — linear, quadratic, cubic, sqrt, sigmoid (smoothstep)
• Live tuning — adjust temperature thresholds and curve shape at runtime, no restart needed
• Fan modes — force fans off, full speed, or back to auto from the command line
• Hysteresis — 2 °C dead-band prevents fan flutter at threshold boundaries
• Clean shutdown — restores hardware AUTO mode on exit
• Minimal logging — one line per fan speed change, heartbeat every 60 s

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Requirements

Component	Details
CPU sensor	k10temp kernel module (AMD Ryzen / EPYC)
Fan controller	nct6687 chip via nct6687d kernel module
Init system	systemd
Shell	bash 4.0+

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Installation

git clone https://github.com/webtemp/dfan.git dfan
cd dfan
sudo ./install.sh

The installer will:

1. Symlink src/dfan and src/dfanctl into /usr/local/sbin/
2. Install and enable the systemd service
3. Create /run/dfan/ (world-writable tmpfs dir) via tmpfiles.d
4. Install a polkit rule so dfanctl works without sudo

Uninstallation

sudo ./uninstall.sh

Stops the service, removes all installed files, and returns fans to hardware AUTO mode.

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Project Structure

dfan/
├── src/
│   ├── dfan            # daemon script
│   ├── dfanctl         # control tool
│   └── dfan-tray       # system tray icon (PyQt6)
├── systemd/
│   ├── dfan.service        # system daemon unit
│   └── dfan-tray.service   # user-level tray unit
├── polkit/
│   └── dfan.rules      # polkit rule (dfanctl without sudo)
├── tmpfiles/
│   └── dfan.conf       # /run/dfan runtime dir
├── install.sh
├── uninstall.sh
└── README.md

Usage

dfanctl --help

Adjust temperature thresholds

dfanctl low 50     # fans start ramping at 50 °C
dfanctl hi  75     # fans hit full speed at 75 °C

Takes effect immediately via signal — no cycle delay.

Change fan curve

dfanctl curve sigmoid
dfanctl curve sqrt
dfanctl curve linear

Takes effect within 5 seconds (next daemon cycle).

Fan modes

dfanctl off        # force all fans OFF (0 PWM)
dfanctl full       # force all fans to 100%
dfanctl auto       # return to temperature-driven curve

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Fan Curves

All curves share the same endpoints (FAN_T_LO → 0%, FAN_T_HI → 100%). They differ in how aggressively fans ramp through the middle range.

Temp (°C)	linear	quadratic	cubic	sqrt	sigmoid
50	0%	0%	0%	0%	0%
55	20%	4%	1%	45%	16%
60	40%	16%	6%	63%	50%
65	60%	36%	22%	77%	68%
70	80%	64%	51%	89%	97%
75	100%	100%	100%	100%	100%

100% ┤                                         ╭─── linear
     │                                    ╭────╯
 75% ┤                          ╭─────────╯         sqrt
     │                    ╭─────╯
 50% ┤              ╭─────╯                       sigmoid
     │         ╭────╯
 25% ┤    ╭────╯                               quadratic
     │╭───╯
  0% ┼─────────────────────────────────────────────────▶
    50°C  55°C  60°C  65°C  70°C  75°C

• sqrt — spins up quickly, good for reactive cooling
• sigmoid — smooth S-curve, gentle at both ends, natural feeling (default)
• quadratic / cubic — whisper-quiet until the upper range, then aggressive

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Monitoring

# Live log output
journalctl -fu dfan

# Current service status
systemctl status dfan

Example log output:

14:03:12  CPU 55°C → setting fans to 45%
14:04:12  CPU 55°C — fans steady at 45%
14:05:33  curve → sigmoid
14:07:41  SIGUSR1 — FAN_T_LO → 45°C (ramp now 45–75°C)
14:08:00  mode → full — fans forced to 100%
14:08:10  mode → auto

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Configuration

Default values live at the top of src/dfan. The most commonly tuned parameters:

Variable	Default	Description
FAN_T_LO	50	°C where ramp begins
FAN_T_HI	75	°C where fans hit full speed
FAN_CURVE	sqrt	Curve shape
FAN_PWM_MAX	230	PWM cap (~90% — hardware protection)
FAN_HYST	2	°C dead-band to prevent flutter
INTERVAL	5	Seconds between cycles

These can also be changed at runtime with dfanctl without editing the file.

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How It Works

1. On start, the daemon locates k10temp and nct6687 dynamically via /sys/class/hwmon/hwmon*/name — no hardcoded paths
2. Every 5 seconds it reads the CPU temperature and maps it through the configured curve to a PWM value
3. It only writes to sysfs when the target PWM actually changes (hysteresis prevents thrashing)
4. SIGUSR1 / SIGUSR2 update FAN_T_LO / FAN_T_HI live; curve and mode changes are picked up by polling /run/dfan/
5. On exit (shutdown, SIGTERM, Ctrl-C), all fan channels are restored to hardware AUTO mode

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System tray (optional)

A PyQt6 tray icon is installed alongside the daemon. It shows current fan % inside a colour-coded ring (green/yellow/orange/red by CPU temp, blue when forced off, red when forced full) and a tooltip with full stats. Right-click menu lets you switch mode or curve without opening a terminal.

sudo pacman -S python-pyqt6                       # or your distro's equivalent
systemctl --user start dfan-tray                  # run now
systemctl --user enable dfan-tray                 # auto-start on login (default)
systemctl --user status dfan-tray                 # check it
journalctl --user -u dfan-tray -f                 # tail logs

The tray runs as a user systemd service, not system-wide — logs are per-user and it starts when your graphical session does.

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License

MIT © webtemp