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upmon

upmon is a simple command line utility to monitor and summarise changes to certain properties of power devices (such as battery percentage, whether an AC cable is plugged in, etc). It does this by looking for messages sent over D-Bus by the UPower service. Detected changes are then written to standard output (or a specified file) in a simple, line-based format.

I wrote upmon because I wanted a very simple way for scripts to react to power-related events on my laptop (such as changes to battery level) without having to poll frequently or parse the more complex output returned by some other tools.

Installation

Because upmon works by interacting with UPower, you need to be running a Linux system with the upowerd service running. For now, the easiest way to install (assuming you have cargo installed) is to clone this repository and use cargo install:

git clone https://github.com/bunburya/upmon.git
cd upmon
cargo install --path .

upmon should then appear in your $HOME/.cargo/bin (or wherever cargo install places binaries).

Usage

upmon called with no arguments will do nothing. Typical usage is to provide one or more --path arguments, telling it which power devices to monitor. --path takes two parameters: the path to the device, and a comma-seperated list of properties to monitor.

upmon --path /org/freedesktop/UPower/devices/battery_BAT0 State,Percentage \
      --path /org/freedesktop/UPower/devices/line_power_AC Online

This will output lines to your terminal as changes to the specified properties are observed. For example, after disconnecting your AC cable, you might see something like:

/org/freedesktop/UPower/devices/battery_BAT0 State=Discharging Percentage=81
/org/freedesktop/UPower/devices/line_power_AC Online=false
/org/freedesktop/UPower/devices/battery_BAT0 Percentage=80

Currently only a handful of properties are supported. You can see a list of supported properties by passing the --list-properties argument. A full list of UPower device properties and their descriptions can be found here. If there are additional properties you would like upmon to support, feel free to open an issue or submit a pull request.

Configuring output

You can configure the separator between property name and value using the --separator argument, and the delimiter between different property-value pairs using the --delimiter argument. For example, the following command:

upmon --path /org/freedesktop/UPower/devices/battery_BAT0 UpdateTime,State,Percentage \
      --separator "::" --delimiter "||"

would produce output like the following:

/org/freedesktop/UPower/devices/battery_BAT0 UpdateTime::2024-02-11T20:42:26Z||State::Discharging

You need to be careful that any separators or delimiters do not conflict with strings used in the output itself. upmon does not provide any guarantees in that respect.

You can tell upmon to add an ISO 8601-formatted timestamp to the output with the --timestamp argument.

upmon --path /org/freedesktop/UPower/devices/battery_BAT0 State,Percentage \
      --timestamp

will output something like:

2024-02-11T20:39:49.559Z /org/freedesktop/UPower/devices/battery_BAT0 State=Charging

Finally, you can tell upmon to write to a specific file, rather than standard output, by providing the --output-file argument. This will open any file (whether or not it already exists) and append new lines to the end of the file.

Other options

upmon has some other options not discussed here. Pass the --help argument for a summary of all the available options.

Development

upmon was written in Rust. It relies on a handful of well-known dependencies to handle command line argument parsing, interaction with D-Bus and timestamp formatting. You can see these in Cargo.toml.

If you encounter any bugs or have any (reasonable) feature requests, feel free to file an issue.