Ubuntu Linux for Robotics · Lesson 51 of 96

Lifecycle nodes

Managing node states with ros2 lifecycle and start-up order on a robot.

Estimated time · 45–75 min

Learning goals

What you will understand

Explain lifecycle nodes in your own words
Use it in a small workstation example
Verify the result instead of assuming it worked

Understand the idea first

The mental model

A lifecycle node has states: unconfigured, inactive, active and finalized. Transitions (configure, activate, deactivate, cleanup) are triggered by a manager or by you from the terminal, which lets a robot bring up hardware in a controlled order.

On Ubuntu use ros2 lifecycle nodes to list managed nodes, ros2 lifecycle get /node for the state and ros2 lifecycle set /node configure|activate|deactivate|cleanup to change it. Nav2 uses a lifecycle manager to start its servers this way.

Guided lesson

Work through these steps

1.
Open a terminal and record the current state before changing anything.
2.
Read the lifecycle nodes commands and predict what each one does.
3.
Run the commands one at a time and compare each output with your prediction.
4.
Write the commands that worked in a setup note you can repeat later.

Worked example

Read it before you run it

ros2 lifecycle nodes
# List nodes that support lifecycle management.
ros2 lifecycle get /driver
# Read the current state (unconfigured).
ros2 lifecycle set /driver configure
# Move to inactive: resources allocated.
ros2 lifecycle set /driver activate
# Move to active: the node starts working.
ros2 lifecycle set /driver deactivate
# Pause it without destroying it.

What the example is doing

1.Lines without sudo only inspect or change files you own; sudo authorizes a system-wide change.
2.Read command output before moving to the next line. Stop if names, versions, disks, or paths differ from the lesson.
3.Comments beginning with # explain safety checks and are not executed by the shell.

Watch it run · Messages between nodes

See what this code does

The terminal types this lesson's practice solution and runs it. The scene shows the kind of robot behaviour that code drives. It plays by itself and loops.

Practice code

Now type it yourself

Open a terminal, run the starter line by line (or save it as practice.sh and run bash practice.sh), and replace every TODO with your own command.

ros2 lifecycle set /driver configure
# TODO: activate /driver and print its state with ros2 lifecycle get

Expected output

primary state: active

Stuck? Show the full solution (try it yourself first)

ros2 lifecycle set /driver configure
ros2 lifecycle set /driver activate
ros2 lifecycle get /driver

Expected result

How you know it worked

Each command completes without an unexplained error.
Your notes contain the command, the important output, and what it proves.

Practical exercise

Apply the lesson

Run a lifecycle node, walk it through configure, activate, deactivate and cleanup from the terminal, and check with ros2 topic echo that messages flow only while it is active.

Before you continue

You recorded the starting state
Every command and output is understood
The change can be repeated from your notes

If something goes wrong

A command says permission denied.

Check ownership and permissions first. Do not add sudo unless the command changes a documented system location.

A command or package is not found.

Check spelling, Ubuntu version, enabled repositories, and whether the previous installation command succeeded.