SenseThing: Easy sensor monitoring for Linux

sensething is a CLI tool for discovering, reading, and logging Linux system sensor data. Its goals are as follows:

Make as many hardware sensors as possible visible from within a single tool,
Provide a human-friendly way of querying specific sensors,
Produce output in formats that are easy to parse (for humans and computers).

Rationale: why use SenseThing instead of lm-sensors?
How SenseThing works
Tutorial
Installation
Discovering your system's sensors
A simple way to read sensor data
Logging sensor data continuously
Monitoring sensor data remotely

Rationale: why use SenseThing instead of lm-sensors?

SenseThing shows all the same data as lm-sensors, plus some additional things:

SenseThing can report CPU and GPU clock frequency data, which is not reported by lm-sensors.
SenseThing supports Nvidia GPUs, and can report many of the same metrics reported by nvidia-smi.

SenseThing fits some use cases that aren't covered by lm-sensors. Here are a couple examples:

Periodically logging sensor data to a CSV file during benchmark testing.
Monitoring remote servers through a simple web UI.

How SenseThing works

SenseThing works by traversing Linux's sysfs. It is aware of the interfaces exposed by the hwmon, drm, and cpufreq kernel modules. Nvidia sensor data is acquired via nvidia-smi.

Installation

For apt-based Linux distros, SenseThing can be installed using one of the deb files available in the GitHub Releases.

On other distros, unfortunately you'll have to install SenseThing manually. Run the following commands to check out this repo and install:

git clone git@github.com:ryukoposting/sensething.git
cd sensething
bundle install
rake install
sensething --version

Discovering your system's sensors

First, you'll want to grab a list of the available sensors on your system:

# these are synonyms, use whichever one you prefer
sensething ls
sensething list-sensors

The ls (a.k.a. "list-sensors") command prints a list of sensors. Here's a truncated example from my 10th gen ThinkPad X1:

acpitz/temperature_1          Temperature Sensor (hwmon1/temp1)
BAT0/voltage_0                Voltage Sensor (hwmon2/in0)
nvme/Composite                Temperature Sensor (hwmon3/temp1)
**snip**
thinkpad/fan_1                Fan (hwmon6/fan1)
thinkpad/pwm_1                PWM (hwmon6/pwm1)
thinkpad/CPU                  Temperature Sensor (hwmon6/temp1)
thinkpad/fan_2                Fan (hwmon6/fan2)
thinkpad/GPU                  Temperature Sensor (hwmon6/temp2)
thinkpad/temperature_3        Temperature Sensor (hwmon6/temp3)
thinkpad/temperature_4        Temperature Sensor (hwmon6/temp4)
**snip**
coretemp/Package id 0         Temperature Sensor (hwmon7/temp1)
coretemp/Core 0               Temperature Sensor (hwmon7/temp2)
coretemp/Core 4               Temperature Sensor (hwmon7/temp3)
coretemp/Core 8               Temperature Sensor (hwmon7/temp4)
coretemp/Core 12              Temperature Sensor (hwmon7/temp5)
coretemp/Core 16              Temperature Sensor (hwmon7/temp6)
**snip**
cpu0/frequency                CPU Frequency (cpufreq/policy0)
cpu1/frequency                CPU Frequency (cpufreq/policy1)
cpu2/frequency                CPU Frequency (cpufreq/policy2)
cpu3/frequency                CPU Frequency (cpufreq/policy3)
cpu4/frequency                CPU Frequency (cpufreq/policy4)
**snip**
card0/frequency               Graphics Frequency (drm/card0)

Skimming through that list, you'll see myriad temperature sensors, a couple fans, a PWM output, battery voltage, and CPU/GPU clock frequencies.

Some of the sensors have pretty self-evident names, like BAT0/voltage_0 and coretemp/Core 0. SenseThing always tries to give descriptive, human-friendly names to all sensors it discovers.

A simple way to read sensor data

Let's grab a value from one of those sensors:

# 'r' is a synonym for 'read'
sensething r -s BAT0/voltage_0
sensething read -s BAT0/voltage_0

To read a sensor, use the r (a.k.a. "read") command to fetch sensor values in a human-friendly format. Here's what I got when I ran that command:

BAT0/voltage_0                16490.0 mV

SenseThing happily prints the sensor's name, followed by its value, with its units. Let's try adding some more sensors to our query:

sensething r -s BAT0/voltage_0 -s thinkpad/CPU -s card0/frequency

You can add as many sensors as you want, and SenseThing will dutifully print out their values for you:

BAT0/voltage_0                16487.0 mV
thinkpad/CPU                  47.0 °C
card0/frequency               300.0 MHz

Logging sensor data continuously

Let's say you're running some benchmarks, and you want to keep an eye on CPU and GPU temperatures during the test. SenseThing's l (a.k.a. "log") command is made for that purpose:

# 'l' is a synonym for 'log'
sensething l -s thinkpad/CPU -s thinkpad/GPU
sensething log -s thinkpad/CPU -s thinkpad/GPU

SenseThing will start printing out a CSV file containing the measurements. Every 5 seconds, a new line of data will be printed.

thinkpad/CPU,thinkpad/GPU
43.0,43.0
43.0,42.0
43.0,45.0

Units of measurement

To include units of measurement in the header row, add the -u (a.k.a "--units") flag:

sensething l -u -s thinkpad/CPU -s thinkpad/GPU

The sample output above would look like this when the -u flag is added:

thinkpad/CPU [°C],thinkpad/GPU [°C]
43.0,43.0
43.0,42.0
43.0,45.0

Changing the sampling rate

To make SenseThing record data every 2 seconds instead of 5, use the -i (a.k.a. "--interval") flag:

sensething l -i 2

-i accepts decimal numbers like 4.2 or 0.5, as well.

Nvidia users: Please note that, while you can still set a faster interval, data from nvidia-smi won't actually change faster than once per second.

Timestamps

Depending on your use case, it may also be useful to include timestamps with your data. The -t flag (a.k.a. "--timestamp") facilitates this:

sensething l -t  # same thing as "-t seconds"
sensething l -t seconds
sensething l -t millis

With -t seconds and -t millis, SenseThing's timestamps will show the time elapsed since the program started. This is usually the most useful form when recording data during benchmarking.

When an absolute wall-clock time is desired, timestamps can also be formatted in standard ISO 8601 standard forms:

sensething l -t iso8601           # yyyy-mm-ddThh:mm:ss+ZZZZ
sensething l -t iso8601-millis    # yyyy-mm-ddThh:mm:ss.sss+ZZZZ

Output formats: JSON and CSV

SenseThing's logging feature defaults to CSV. However, it also supports JSON output, thanks to the -f (a.k.a. "--format") flag:

sensething l -f json
sensething l -f csv   # this is the default

Monitoring sensor data remotely

If you want to monitor a system's sensors remotely, you could simply pipe sensething l -f json ... into netcat, but this approach has its fair share of flaws. SenseThing's s command (a.k.a "serve") exposes an HTTP server that provides more refined access to the system's sensors.

# These are synonyms, use whichever one you prefer
sensething s
sensething serve

Run sensething s, open your browser, and navigate to localhost:4567. You'll see a page that looks something like this:

Pretty? Not really. Informative? Absolutely!

Adding Accept: text/json to your request will cause SenseThing to respond with JSON instead of HTML.

The server's configuration can be altered using the -a and -p options, which set the server's address and port respectively. For example,

sensething s -a 0.0.0.0 -p 80

ryukoposting/sensething