ROS Master (roscore)

The central process in ROS 1 that registers nodes and helps them find each other.

The ROS Master is the central coordinating process in ROS 1 (the first generation of the Robot Operating System), typically started with the roscore command, which also brings up the Parameter Server and the logging node rosout alongside it. When a node — a process that does one job — starts up, it registers with the Master which topics (data channels) it publishes or subscribes to, and which services it offers. The Master's only job is to tell publishers and subscribers each other's addresses; after that, data flows directly between nodes, peer to peer, without passing through the Master. Its weakness is being a single point of failure: if the Master dies, no new node can join, and communicating across machines requires setting ROS_MASTER_URI on each one. ROS 2 removed the Master entirely, letting the underlying DDS layer discover nodes automatically instead.

ExampleTo run a robot in ROS 1: open one terminal and run roscore, then use rosrun to start the camera driver and mapping node; a second computer must point ROS_MASTER_URI at this machine to see its topics.

Also called

roscore, rosmaster

Related

Robot Operating System · Node (ROS) · Topic (ROS) · ROS Parameter Server · Robot Operating System 2 · Data Distribution Service

Sources

ROS Wiki: Master
ROS Wiki: roscore