Temperature Monitoring on Linux

Temperature Monitoring on Linux

PhotoStructure monitors hardware temperatures on Linux and will automatically pause the sync process when any sensor exceeds the maxTempCelsius threshold (default: 80°C / 176°F). This prevents hardware damage from sustained high temperatures during CPU-intensive operations like image hashing and video transcoding.

PhotoStructure reads temperatures from three sources, and merges the results:

  1. lm-sensors — the standard Linux sensor monitoring package
  2. hwmon sysfs — direct kernel sensor readings from /sys/class/hwmon/
  3. thermal zones — ACPI and platform thermal data from /sys/class/thermal/

No root access is required for any of these methods.

lm-sensors

lm-sensors is the most full-featured option. It provides calibrated readings, human-readable sensor labels, and supports a wide range of hardware.

Installation

On Debian/Ubuntu:

sudo apt install lm-sensors
sudo sensors-detect

On Fedora/RHEL:

sudo dnf install lm_sensors
sudo sensors-detect

On Arch Linux:

sudo pacman -S lm_sensors
sudo sensors-detect

The sensors-detect command scans your hardware and configures the appropriate kernel modules. Answer “yes” to its prompts to load the detected modules.

After setup, verify it’s working:

sensors

You should see output listing your CPU, motherboard, and other sensor temperatures.

References

hwmon sysfs

The Linux kernel exposes hardware sensor data directly through the hwmon sysfs interface at /sys/class/hwmon/. PhotoStructure reads these files directly, so temperature monitoring works even without lm-sensors installed.

This is especially useful in Docker containers and minimal Linux installs where installing additional packages may not be desirable.

Each sensor chip gets a directory like /sys/class/hwmon/hwmon0/ containing:

  • name — the kernel driver name (e.g., k10temp, nct6798, nvme)
  • temp1_input, temp2_input, … — temperatures in millidegrees Celsius

PhotoStructure automatically reads all available hwmon sensors. If lm-sensors is also installed, PhotoStructure deduplicates results so you don’t see the same sensor twice.

Docker

For Docker containers, you may need to bind-mount the hwmon sysfs directory:

volumes:
  - /sys/class/hwmon:/sys/class/hwmon:ro

NVMe drives

NVMe SSDs typically expose their temperatures through hwmon automatically via the kernel’s NVMe driver, with no additional configuration needed.

References

Thermal zones

The Linux kernel’s thermal framework exposes temperature data at /sys/class/thermal/thermal_zone*/. This interface is commonly used by:

  • ACPI thermal zones on x86 systems (type: acpitz)
  • Realtek SoCs in some Synology NAS models
  • ARM platforms like Raspberry Pi

Each thermal zone directory contains:

  • type — a label like acpitz, x86_pkg_temp, or cpu-thermal
  • temp — the current temperature in millidegrees Celsius

PhotoStructure reads all available thermal zones automatically.

Docker

For Docker containers, bind-mount the thermal sysfs directory:

volumes:
  - /sys/class/thermal:/sys/class/thermal:ro

References

SATA/SAS drive temperatures

SATA and SAS hard drives report their temperatures through S.M.A.R.T. monitoring. On Linux, the drivetemp kernel module exposes these temperatures through the hwmon sysfs interface, making them readable without root access.

Enabling drivetemp

Load the module:

sudo modprobe drivetemp

To load it automatically on boot, create a module configuration file (see modules-load.d(5)):

echo drivetemp | sudo tee /etc/modules-load.d/drivetemp.conf

Verify it’s working:

# Look for drivetemp entries in hwmon
for h in /sys/class/hwmon/hwmon*; do
  name=$(cat "$h/name" 2>/dev/null)
  if [ "$name" = "drivetemp" ]; then
    temp=$(cat "$h/temp1_input" 2>/dev/null)
    echo "$h: ${temp%???}.${temp: -3}°C"
  fi
done

Why not smartctl?

The traditional tool for reading drive temperatures is smartctl, but it requires root access to query SATA/SCSI devices. The drivetemp kernel module provides the same temperature data through hwmon sysfs files that are readable by any user.

Docker

For Docker containers, the drivetemp module must be loaded on the host (not inside the container), and /sys/class/hwmon must be bind-mounted as described above.

Synology NAS

Synology DSM may already expose drive temperatures through hwmon. If not, you can load the module via SSH:

sudo modprobe drivetemp

Note that Synology DSM may reset loaded modules after a reboot or DSM update. You may need to use a scheduled task to re-load the module on boot.

References

PhotoStructure settings

maxTempCelsius

The temperature threshold at which PhotoStructure pauses sync. Default: 80°C (176°F). Set to 0 to disable temperature monitoring.

excludedSensorNames

A list of glob patterns for sensor names to ignore. Default: ["*calibration*", "*fan*"]. Useful for filtering out sensors that report incorrect or irrelevant readings.

See advanced settings for how to configure these values.