fanctl — simple web UI for nct6775/nct6797 fan control

A minimal Flask app that reads and writes the Linux nct6775 hwmon sysfs files, so you get a browser dashboard with live RPM readings and per-channel Auto/Manual + duty-cycle sliders — built for the MSI B450 (NCT6797D) setup you were testing over SSH, but it'll work for any board using this driver family.

Before you start

The nct6775 kernel module has to be loaded on the TrueNAS host before this container can read/write anything under /sys/class/hwmon. The container does not load the module itself — it only reads/writes the sysfs files that already exist once the host has the module loaded.

Confirm the module is loaded and note which hwmonN path is yours:

sudo /sbin/modprobe nct6775
for d in /sys/class/hwmon/hwmon*; do echo "$d: $(cat $d/name)"; done

Update HWMON_PATH in docker-compose.yml if your number isn't hwmon2 (it can shift between reboots).

Run it

docker compose up -d --build

Then open http://<your-truenas-ip>:5000.

Permissions

Writing to sysfs from inside a container usually needs elevated privileges. The compose file starts with cap_add: SYS_RAWIO, which is enough on most systems. If you still get "Permission denied" errors when moving a slider, uncomment privileged: true in docker-compose.yml instead (broader access, but guaranteed to work).

Persisting across TrueNAS reboots/upgrades

TrueNAS resets anything installed by hand on the base OS. Two things need to survive a reboot:

1. The kernel module — add this to System Settings → Advanced → Init/Shutdown Scripts as a Post Init script (When: Post Init, Type: Command):

   /sbin/modprobe nct6775

2. The container — if you deploy this via docker compose directly on the host (outside the TrueNAS Apps system), make sure restart: unless-stopped is set (already in the compose file) and that Docker itself is set to start on boot. If you instead import this as a TrueNAS custom App, the Apps system handles restart-on-boot for you — just make sure the Init/Shutdown Script above still runs before the app starts, since the container depends on the module already being loaded.

Notes on safety

• Switching a channel to Manual disables the BIOS/EC's own thermal curve for that header until you switch it back to Auto (or reboot).
• If a fan's RPM reads 0 shortly after you lower its duty cycle, it's likely stalled — raise the value. 3-pin (non-PWM) fans typically need a noticeably higher floor than 4-pin PWM fans before they stall.
• This app applies your changes directly and immediately — it does not currently implement its own temperature-based auto-curve. If you want that added (e.g. auto-adjust pwm2 based on CPUTIN), that's a straightforward addition — just say the word.