Fancontrol Parser

A Python utility to automatically update hwmon device numbers in the fancontrol configuration file when they change after system reboot.

Background

On Linux systems using lm-sensors and fancontrol, the hwmon device numbers (e.g., hwmon0, hwmon1) can change between reboots. This causes the fancontrol service to fail since it relies on these device numbers in its configuration. This script automatically detects and updates these numbers, ensuring your fan control settings persist across reboots.

Features

• Handles any number of hwmon entries in /etc/fancontrol (not just coretemp + one fan chip)
• Matches each entry to a live hwmon by DEVPATH (the stable ATA/PCI path), with driver-name fallback when the path alone isn't enough. This is what lets it correctly track devices like drivetemp, which can otherwise end up bound to the wrong disk
• Two-pass placeholder rewrite so hwmon swaps (e.g. hwmon3 <-> hwmon4) don't cascade into wrong values
• Updates the fancontrol configuration file with the new device numbers
• Restarts the fancontrol service automatically
• Dry run mode to preview changes
• Quiet mode for silent operation

Prerequisites

• Python 3
• lm-sensors and fancontrol packages installed
• Root privileges (for modifying /etc/fancontrol)

Installation

1. Clone this repository:

git clone https://github.com/thiswillbeyourgithub/fancontrol-parser.git

Usage

sudo python3 fancontrol_parser.py [--quiet] [--apply]

Options:

• --quiet, -q: Suppress output messages
• --apply, -a: Apply changes (without this flag, runs in dry-run mode)

Example

sudo python3 fancontrol_parser.py --apply

This will:

1. Parse every DEVPATH= / DEVNAME= entry in /etc/fancontrol
2. Match each entry to a live hwmon (by DEVPATH first, driver name as fallback)
3. Rewrite the configuration if any hwmon numbers have changed
4. Restart the fancontrol service

Note: the parser no longer skips when fancontrol.service is already running. fancontrol can be active but still bound to the wrong sensor (common with drivetemp after a hwmon reshuffle), so the check runs unconditionally.

Helper Scripts

generate_hwmon_mappings.sh

A diagnostic script that creates a CSV table mapping hwmon device numbers to their corresponding hardware models and names. This is useful for identifying which hwmon device corresponds to which hardware component when configuring fancontrol.

Usage:

# Generate mapping and save to default location (/etc/fancontrol_mappings)
sudo ./generate_hwmon_mappings.sh
# Save to custom location
sudo ./generate_hwmon_mappings.sh --output-path /path/to/mappings.csv
# Check if mappings have changed without modifying the file
sudo ./generate_hwmon_mappings.sh --check
# Include battery-related devices (by default they are filtered out)
sudo ./generate_hwmon_mappings.sh --no-ignore-battery

Options:

• --output-path PATH: Specify custom output path (default: /etc/fancontrol_mappings)
• --check: Compare current mappings with existing file without modifying it
• --no-ignore-battery: Include battery-related hwmon devices (by default battery devices are filtered out as they can be problematic for some setups)

The script generates a CSV with three columns:

• hwmon: The hwmon device name (e.g., hwmon0, hwmon1)
• device_model: The hardware model if available
• name: The device name (e.g., coretemp, it8792)

This helps you understand which hwmon numbers to use in your fancontrol configuration before running the parser.

Automatic Execution

You can add this script to your system's startup sequence to ensure fan control works correctly after every reboot. One way to do this is by creating a systemd service that runs before the fancontrol service:

# Create a systemd service file
sudo nano /etc/systemd/system/fancontrol-parser.service

Add the following content:

[Unit]
Description=Update hwmon device numbers in fancontrol config
Before=fancontrol.service
After=multi-user.target
[Service]
Type=oneshot
ExecStart=/usr/bin/python3 /path/to/fancontrol_parser.py --apply
[Install]
WantedBy=multi-user.target

Then enable the service:

sudo systemctl enable fancontrol-parser.service

License

AGPLv3

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.