ROS2:Basic

lastmod 2026-10-27created 2026-03-099 edits

Notes on the basics of Robot Operating System 2.

Communication model architecture

TOPIC - many-to-many · async · no reply
SERVICE - 1-to-1 · sync · request/reply
ACTION - 1-to-1 · long-running · goal + feedback + result
PARAMETER - per-node KV store · changeable at runtime
BAG (rosbag2) - record/replay of topic streams — the source of ML training sets from sensor data

URDF

URDF · robot description — geometry + inertia + joints + collision.

URDF (Unified Robot Description Format) is an XML format that represents a robot as a graph of links (link) + joints (joint). rviz2, Gazebo, MoveIt2, and ros2_control all run on the same description. Xacro is a template language that adds macros, variables, and include to URDF; in practice, Xacro is almost always used.

Cheat sheet

Purpose	Command
List nodes	`ros2 node list`
Node details	`ros2 node info /your_node`
Topic list / types / QoS	`ros2 topic list -v · ros2 topic info -v /scan`
Topic contents	`ros2 topic echo /scan`
Topic rate/bandwidth/delay	`ros2 topic hz /scan · bw · delay`
Call a service	`ros2 service call /set_mode my_pkg/srv/SetMode "{mode: 'idle'}"`
Call an action	`ros2 action send_goal /scan my_pkg/action/Scan "{num_samples: 100}"`
Parameters	`ros2 param list · get · set · dump · load`
Show interface definition	`ros2 interface show sensor_msgs/msg/PointCloud2`
Dump TF tree to PDF	`ros2 run tf2_tools view_frames`
One-off check of a specific transform	`ros2 run tf2_ros tf2_echo base_link tool0`
Environment diagnostics	`ros2 doctor --report`
Package path	`ros2 pkg prefix my_pkg`
Log level	`--ros-args --log-level my_node:=debug`

ROS2:Basic

Categories

Communication model architecture

URDF

Cheat sheet

See also