Links and Nodes (LN)

Links and Nodes (LN) is an open-source middleware for building distributed real-time robotic systems. It combines process management with fast publish/subscribe messaging and request/response services, allowing complex multi-process systems to be configured and reproduced from a single text configuration file (.lnc).

Developed at the German Aerospace Center (DLR) since 2010, LN supports robotics applications that require deterministic behavior, low-latency communication, and coordinated process control across multiple hosts and programming languages (C, C++, Python).

Key Features

• Process management -- Spawn, monitor, and control processes with dependency ordering, priorities, and real-time introspection.
• Publish/subscribe topics -- Low-latency messaging via shared memory (local), UDP, or TCP.
• Services (request/response) -- Reliable RPC via Unix domain sockets (local) or TCP (network).
• Multi-language APIs -- C, C++, and Python client libraries with a shared message-definition format.
• Single configuration -- Define processes, topics, services, and dependencies in one .lnc file.
• Manager GUI & CLI -- ln_manager for interactive system monitoring and control (web UI included).

Platform Support

Native install is officially supported on Linux (Ubuntu 22.04+, Debian 12+, ...) only. For macOS and Windows, use the Docker-based installation.

Getting Started

Documentation

• User Guide & Tutorials -- Getting started, configuration, API reference
• Source API: libln/include/ln/ln.h (C), libln/include/ln/cppwrapper.h (C++), python/links_and_nodes/ (Python)

Docker Images

If you prefer to run LN from a container, see docker/README.md for complete Docker usage documentation.

License

The core library (libln) is released under LGPLv3 so it can be dynamically linked into non-GPL projects. All other components (ln_daemon, ln_manager, Python bindings) are released under GPLv3.

How To Contribute

If you want to contribute, please read CONTRIBUTING.md guide first.

DLR-RMC Instructions

For DLR-RMC systems, see README.RMC.md.