Network UPS Tools (NUT)

Network UPS Tools (NUT) is a layered collection of programs designed to monitor and administer UPS (Uninterruptible Power Supply), PDU (Power Distribution Unit), and SCD hardware.

Its architecture consists of three main layers:

1. Drivers: Communicate directly with specific hardware models, translating device-specific protocols into a common compatibility layer.
2. Server (upsd): Caches information from the drivers and serves it over the network to authorized clients.
3. Clients: Monitor status and perform actions (like clean shutdowns) based on data received from upsd.

This layered approach allows multiple systems to monitor a single large UPS and enables centralized management of power devices.

The scripts/installer/ directory contains scripts and data for NUT packaging (formerly known as Eaton IPSS Unix, IPP for Unix, or UPP). It provides an interactive text-mode installer for target deployments, covering:

• Package (re-)installation
• Initial device discovery
• Password setup
• Shutdown handling via helper scripts
• Status overview via helper scripts

The installer relies on the nutconf tool, which is part of the NUT source tree.

NUT provides several libraries to facilitate interfacing with 3rd party programs and internal components:

• libupsclient: Used to interact with the NUT server (upsd).
• libnutclient: Provides a high-level interface to interact with the NUT server.
• libnutscan: Used to discover NUT-supported devices.

Note on Installation: Runtime libraries are installed by default. To install development files (headers, static/shared libraries, and compilation helpers), you must provide the --with-dev flag to the configure script during the build process.

NUT provides mechanisms to manage drivers as systemd service instances using the nut-driver-enumerator.sh script and the upsdrvsvcctl tool. There are two ways to deploy these services:

1. Daemon Mode (nut-driver-enumerator-daemon* units): Runs the enumerator as a continuous daemon to regularly inspect and apply NUT configurations to OS service units. This is intended for monitoring systems with dynamic power devices or where filesystem event monitoring is unreliable.
2. One-shot Mode (nut-driver-enumerator.* units): Runs the script once per trigger (typically during system boot or when configuration changes are detected by systemd).

NUT has deprecated the Master/Slave terminology in favor of Primary/Secondary modes for upsmon clients.

• Configuration: Keywords in upsd.users and upsmon.conf for Master/Slave are supported for backwards compatibility, but they are no longer documented.
• Protocol Behavior: upsmon now attempts to elevate privileges with a PRIMARY <ups> request first, falling back to MASTER <ups> for compatibility with older upsd servers.
• Implementation: The protocol now returns OK PRIMARY-GRANTED for new clients and OK MASTER-GRANTED for legacy clients.

To use the NUT access via FUSE proof-of-concept, you must first install FUSE development libraries and build the execfuse daemon.

Prerequisites:

• Debian-like systems: apt install libfuse-dev
• MacOS (via Homebrew): brew install --cask macfuse@dev

Build steps:

1. Clone the execfuse repository.
2. Build using make to produce the execfuse binary.

apt install libfuse-dev  # For Debian-like systems

# Build execfuse
git clone https://github.com/vi/execfuse
cd execfuse
make && ls -la execfuse

NUT supports integrating non-native protocols as live-stream input for the dummy-ups driver. An example implementation is provided in scripts/external_apis. To enable this capability during build, use the following configure flag:

configure --enable-extapi-enphase

After installing or modifying udev rules, you can trigger the rules to become active immediately without a system reboot by refreshing the device subsystem using udevadm trigger.

udevadm trigger --subsystem-match=usb_device