ROS2 Bags (rosbag2) — Complete Guide | R2BOT
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rosbag2 records and replays ROS2 topics for offline analysis and regression testing. The black-box recorder of every modern robot.
The ros2 ecosystem concept: rosbag2 records and replays ROS2 topics for offline
rosbag2 is the ROS2 tool to record any set of topics into a single time-stamped file (a 'bag') and later replay them as if the live robot were running. It is the standard way to capture data for offline analysis, regression tests, and CI pipelines.
💡 Think of it like…
Think of it like a household object that does the same job — the underlying idea is the same, just adapted for robots.
Why it matters
Without ros2 bags (rosbag2) — complete guide | r2bot, many ros2 ecosystem systems in robotics simply couldn't work.
ROS2 Bags (rosbag2)
What is ROS2 Bags (rosbag2)?
rosbag2 is the ROS2 tool to record any set of topics into a single time-stamped file (a 'bag') and later replay them as if the live robot were running. It is the standard way to capture data for offline analysis, regression tests, and CI pipelines.
How It Works
From the command line, ros2 bag record /scan /cmd_vel /tf writes all messages on the listed topics into a MCAP or SQLite-backed bag with nanosecond timestamps. ros2 bag play reads the bag and republishes the messages with the original timing — your subscribers cannot tell whether they are reading from a live robot or a replayed bag. Bags can be sliced, filtered, and converted with ros2 bag subcommands.
Real-World Example
Every Nav2 release runs regression tests on stored bag files. Boston Dynamics customers record bag files when robots misbehave and ship them to support. Indian autonomous-vehicle teams (Swaayatt, Flux Auto) record terabytes of bag data daily for training and replay.
Why It Matters for Robotics
Without bag recordings, robotics debugging is nearly impossible. Capturing what the robot saw at the moment of failure — and replaying it offline — is the foundation of modern robotics engineering practice.
Try It Yourself
Record a bag while you drive a TurtleBot3 in Gazebo. Stop the simulator. Run ros2 bag play <bag> while RViz2 is open. The robot appears to move in RViz exactly as it did before — pure replay magic.
Quick Quiz
Quick Quiz
3 questions
1.A rosbag2 file captures:
2.The default modern storage format for rosbag2 is:
3.Bag files are essential for:
Further Reading
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Last updated · 2026-05-21
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