Waybar Fan Speed: Easier Monitoring

Have you ever found yourself staring at your Waybar, wishing you could easily display your computer's fan speed? It’s a common desire for many users who want a quick glance at their system's performance and thermal health. Currently, to get your fan speed showing up on Waybar, you often need to dive into the world of bash scripting. This can be a bit daunting if you're not already comfortable with shell scripting. You might be wondering, "Why is it so hard to just get a fan speed format?" This article aims to explore that very question, looking at the current situation with Waybar and fan speed monitoring, and discussing why a more integrated solution would be incredibly beneficial.

We understand the need for this functionality. Many users, including yourself, have pointed out that Waybar is quite capable of running external exec commands, which is fantastic for pulling in data from various sources. However, the frustration arises when you can't simply use an internal command or a readily available format specifier for something as common as fan speed, much like how tools like Conky manage to do it seamlessly. Conky, for instance, can directly execute commands like sensors and then parse the output using grep and cut without requiring you to write and maintain a separate bash script. This makes it feel like a missed opportunity when Waybar, a highly customizable bar, doesn't offer a similar built-in convenience for fan speed. The current workaround of creating a custom bash script for each fan speed metric can lead to clutter and makes configuration management more complex than it needs to be. Imagine trying to monitor multiple fans – each would potentially need its own script, or a very complex single script, which isn't ideal for a clean and efficient setup.

Let's delve a little deeper into why this might be the case and what the current methods involve. When you look at system monitoring, temperature sensors are often handled through specific kernel interfaces, commonly exposed via /sys/class/hwmon/. As you've correctly identified, paths like /sys/class/hwmon/hwmon2/temp_input work beautifully because Waybar (or the underlying system it interacts with) has a pre-defined format specifier, like {temperatureC}°C {icon}, to interpret and display this data. This means Waybar knows how to read that specific file, understand its value represents temperature in Celsius, and apply a visual representation. The ease with which you can display temperature is a testament to good design when such formats are available. However, when it comes to fan speed, the situation is a bit different. The relevant files, such as /sys/class/hwmon/hwmon5/fan1_input or /sys/devices/platform/nct6775.656/hwmon/hwmon5/fan1_input, contain the raw fan speed data, typically in revolutions per minute (RPM). The challenge is that Waybar, by default, doesn't have a specific internal format specifier like {RPM} or {Speed} that directly understands and processes these fan*_input files. Therefore, to display this raw number meaningfully, you're currently pushed towards using the exec module, which requires you to write and execute an external command or script.

This reliance on external scripts for fan speed is precisely the point of friction. While exec is powerful, it adds a layer of complexity. You need to ensure the script is executable, that it correctly targets the right hwmon path (which can vary between systems and hardware), and that it outputs the data in a format Waybar can understand. For example, if you were to use cat /sys/class/hwmon/hwmon5/fan1_input, Waybar would simply display the raw number outputted by cat. To make it more user-friendly, like showing "647 RPM", you'd need a script that not only reads the file but also appends the " RPM" string. The same applies if you want to monitor multiple fans. The command cat /sys/class/hwmon/hwmon5/fan[1-7]_input is a neat trick for a shell to read multiple files, but Waybar's exec module typically processes the output of a single command. So, to display multiple fan speeds, you'd likely need a more sophisticated script that iterates through the fan inputs and formats the output accordingly, perhaps separated by spaces or newlines, which then needs to be parsed by Waybar's exec module, or displayed as a single block of text.

The comparison to Conky's ${execi 1 sensors nct6798-isa-0290 | grep fan1 | cut -c 26-30} is spot on. Conky has a robust system for executing and parsing commands internally. The execi 1 part tells Conky to execute the command every 1 second. The command itself (sensors nct6798-isa-0290 | grep fan1 | cut -c 26-30) runs the sensors utility, filters for fan1 using grep, and then extracts the relevant digits using cut. Conky then directly uses this output in its configuration. This is the kind of integrated, script-free experience many users desire for Waybar. The desire is not to reinvent the wheel but to have a similar level of convenience for fan speed monitoring as is already available for temperature or other common metrics. It simplifies the user experience significantly, reduces the potential for errors in scripting, and makes Waybar configurations cleaner and easier to maintain. The core issue boils down to Waybar's module design and the availability of specific formatters for hardware sensor data beyond just temperature.

Understanding the hwmon Interface

To truly appreciate why fan speed isn't as straightforward as temperature in Waybar, it's helpful to understand the Linux hwmon (hardware monitoring) subsystem. This is the kernel's interface for exposing hardware sensor data, including temperatures, voltages, fan speeds, and fan control capabilities, to userspace. Different hardware monitoring chips on motherboards and graphics cards are detected by the kernel, and each is assigned an hwmon device, typically found under /sys/class/hwmon/hwmonX/ (where X is a number). Within each hwmon directory, you'll find various files representing specific sensor readings and controls.

For temperature, you commonly find files like tempX_input (where X is a number, e.g., temp1_input), which provides the current temperature reading in millidegrees Celsius. Waybar's {temperatureC} format specifier directly interprets this, converting it to degrees Celsius for display. This is a standardized and well-supported format. However, fan speed is reported differently. You'll typically find files named fanX_input (e.g., fan1_input), which reports the fan speed in RPM (Revolutions Per Minute). Crucially, there isn't a universal kernel standard that Waybar can directly hook into for formatting these fanX_input values into a user-friendly string like "{RPM}" or "{Speed}" out-of-the-box.

The reason for this difference in implementation for fan speed versus temperature often stems from how these values are physically measured and the level of interpretation required. Temperatures are usually direct readings from sensors, and the millidegree Celsius format is fairly consistent. Fan speeds, while also direct readings from tachometer signals, might require additional context or scaling that isn't standardized across all hwmon drivers or hardware. For instance, some systems might report fan speed as a raw count, others might have associated fanX_label files indicating the fan's purpose (e.g., "CPU Fan", "System Fan"), and there might even be related files for fan control (pwmX, fanX_enable).

This lack of a universally defined display format for fan speed within the hwmon interface is the primary bottleneck. Waybar developers would need to decide on a consistent way to interpret and present these fanX_input values. Should it automatically append "RPM"? Should it assume the value is always in RPM? What if a user wants to display other fan-related information? The complexity of covering all potential hardware variations and user needs without a clear standard makes it a challenging feature to implement as a simple, internal format specifier.

The exec Module: A Powerful Workaround

Given the current limitations, the exec module in Waybar remains the most versatile way to incorporate fan speed data. It's designed precisely for situations where Waybar needs to display information that isn't directly handled by its built-in modules or formatters. By using exec, you're essentially telling Waybar: "Go run this command, get its output, and display that output in this module." This is why it works for temperature when you might use a command like cat /sys/class/hwmon/hwmon2/temp1_input and then pipe it through awk '{printf "%.1f°C", $1/1000}' to format it correctly before Waybar displays it. The key is that the exec module captures whatever text string your command outputs.

Let's break down how you'd typically use exec for fan speed, building on your examples. Suppose you want to display the speed of fan1 found at /sys/devices/platform/nct6775.656/hwmon/hwmon5/fan1_input. Your exec configuration in Waybar might look something like this:

{
    "name": "Fan Speed",
    "module": "custom/script",
    "format": "{}",
    "exec": "echo $(cat /sys/devices/platform/nct6775.656/hwmon/hwmon5/fan1_input) RPM"
}

In this example:

• "name": "Fan Speed" gives your module a descriptive name.
• "module": "custom/script" indicates you're using a custom script or command.
• "format": "{}" tells Waybar to use the output of the exec command as the content for this module. The {} placeholder will be replaced by the output.
• "exec": "echo $(cat /sys/devices/platform/nct6775.656/hwmon/hwmon5/fan1_input) RPM" is the command that Waybar will run. It first uses cat to read the value from the fan1_input file. The $(...) syntax is a shell command substitution, which executes the cat command and inserts its output. Then, echo prints that value followed by the string " RPM". So, if cat outputs 647, the final output to Waybar will be 647 RPM.

This approach provides a flexible solution. You can modify the exec command to perform more complex operations. For instance, if you want to monitor multiple fans and display them in a single module, you could create a small bash script that reads all relevant fan*_input files, formats them nicely (perhaps with labels), and then have the exec module simply call that script. Your command might become something like exec: "~/scripts/monitor_fans.sh" where monitor_fans.sh contains logic like:

#!/bin/bash

# Example script to monitor multiple fans

read -r fan1_speed < /sys/devices/platform/nct6775.656/hwmon/hwmon5/fan1_input
read -r fan2_speed < /sys/devices/platform/nct6775.656/hwmon/hwmon5/fan2_input

echo "Fan1: ${fan1_speed} RPM, Fan2: ${fan2_speed} RPM"

This exec module approach, while requiring a bit of setup, is powerful because it leverages the shell's capabilities to fetch, process, and format virtually any data that can be accessed from your system. It ensures that you can get your fan speed displayed, even if it’s not a direct, built-in format specifier.

The Case for Native Support

While the exec module is a functional solution, the persistent desire for a native format specifier for fan speed in Waybar highlights a broader goal: simplifying user configuration and enhancing usability. Imagine a scenario where you're setting up Waybar for the first time, or perhaps on a new machine. You want to add your fan speed. With a native format like {fanRPM} or {fanSpeed}, the configuration would be as simple as:

{
    "name": "Fan Speed",
    "module": "hwmon",
    "format": "{fan1RPM} RPM",
    "hwmon-path": "/sys/class/hwmon/hwmon5/fan1_input"
}

This would be incredibly intuitive. The hwmon module would know exactly how to read the fan1_input file, interpret it as RPM, and display it. The user wouldn't need to worry about cat, echo, shell substitutions, or potential path variations across different systems. This ease of use is what makes native support so appealing and contributes to a better user experience.

Moreover, native support often implies better integration and potentially more features. If Waybar were to implement native fan speed support, it could potentially offer:

• Automatic RPM detection: The module could intelligently determine if the value is in RPM.
• Handling of multiple fans: A single hwmon module might be able to monitor and display multiple fans with different configurations (e.g., format: "CPU: {fan1RPM} | SYS: {fan2RPM}").
• Error handling: Native modules can be designed to gracefully handle cases where a fan*_input file is missing or inaccessible, perhaps displaying a placeholder like -- RPM or an error message, rather than the module simply disappearing or showing raw error output.
• Performance optimization: While exec is generally efficient, native code can sometimes be more optimized for specific tasks, though the difference might be negligible for simple sensor readings.

The argument isn't that the exec module is broken; it's that a dedicated format specifier would elevate the configuration experience from