# Tutorial 1: ROS 2 Basics

:::{admonition} Learning Objectives
:class: learning-objs
- How to use common `ros2` CLI commands
- Running ROS 2 nodes with `ros2 run`
- Launching ROS2 nodes with `ros2 launch`
- Observing ROS2 system with `ros2 <topic|node>`
- Observing ROS2 system with RQT
  :::

## Connecting to the Container
---
:::{warning} The container `ros2-demo` must be running!
See, [Using The ROS2 Demo Container](../../setup/using_container.md).
:::

Open the tutorial_1 directory in VSCodium by directing your browser to:
:::{div} url-callout
<https://localhost:8087/?folder=/home/robot/ros2-vsc-demo/tutorials/tutorial1>
:::

Or going to `File->Open Folder` in VSC and selecting `/home/robot/ros2-vsc-demo/tutorials/tutorial1`.

```{figure} /_static/images/getting_started_vsc_task.png
:alt: placeholder
:width: 60%
:align: center
VSCodium task to launch container's openvscode-server.
```

## Running ROS 2 Nodes
Build workspace:

::::{div} grouped-block
```console
~/ros2-vsc-demo/tutorials/tutorial1/tutorial_1_ws$ colcon build
```
```console
Starting >>> mypkg1 
...
Finished <<< mypkg1 [0.73s]          

Summary: 1 package finished [0.78s]
```
::::


Source workspace:

::::{div} grouped-block
```console
~/ros2-vsc-demo/tutorials/tutorial1/tutorial_1_ws$ colcon build
```
```console
Starting >>> mypkg1 
...
Finished <<< mypkg1 [0.73s]          

Summary: 1 package finished [0.78s]
```
::::


Open two shells and run the following:

::::{div} grouped-block
```console
$ ~/ros2-vsc-demo/tutorials/tutorial1/tutorial_1_ws$ ros2 run mypkg1 talker 
```
```console
[INFO] [1779739548.456968934] [talker_node]: Publishing: "Hello World: 0"
[INFO] [1779739548.937330081] [talker_node]: Publishing: "Hello World: 1"
...
```
::::

::::{div} grouped-block
```console
$ ~/ros2-vsc-demo/tutorials/tutorial1/tutorial_1_ws$ ros2 run mypkg1 listener 
```
```console
[INFO] [1779739598.667475455] [talker_node]: Publishing: "Hello World: 0"
[INFO] [1779739599.157543411] [talker_node]: Publishing: "Hello World: 1"
...
```
::::

:::{caution}
Each shell must have the workspace sourced for commands like `ros2 run` to know
 where to find the packages and nodes!.
:::



## Launch ROS 2 Nodes
Before we observe a ROS 2 system we need to have one! We will use a **launch
file**

To do this, open a shell<sup>[[?]](tutorial_01.md#accessing-a-shell)</sup> in
the container. 

In the directory `/home/robot/ros2-vsc-demo/tutorials/tutorial1` there will be a directory `tutorial_1_ws`. 

`cd` into that directory by running:
```console
$ cd tutorial_1_ws
```

Then, run:
::::{div} grouped-block
```console
~/ros2-vsc-demo/tutorials/tutorial1/tutorial_1_ws$ colcon build
```
```console
Starting >>> mypkg1 
...
Finished <<< mypkg1 [0.73s]          

Summary: 1 package finished [0.78s]
```
::::


Then source the built workspace:
```console
~/ros2-vsc-demo/tutorials/tutorial1/tutorial_1_ws$ source install/setup.bash
```

And run the launch file:
::::{div} grouped-block
```console
~/ros2-vsc-demo/tutorials/tutorial1/tutorial_1_ws$ ros2 launch mypkg1 demo.launch.py 
```
```console
[INFO] [launch]: All log files can be found below /home/robot/.ros/log/2026-05-25-19-59-51-613584-06d685a94a45-34527
[INFO] [launch]: Default logging verbosity is set to INFO
[INFO] [talker-1]: process started with pid [34530]
[INFO] [listener-2]: process started with pid [34531]
[talker-1] [INFO] [1779739192.331062106] [talker_node]: Publishing: "Hello World: 0"
[listener-2] [INFO] [1779739192.331352416] [listener_node]: I heard: "Hello World: 0"
[talker-1] [INFO] [1779739192.826401701] [talker_node]: Publishing: "Hello World: 1"
[listener-2] [INFO] [1779739192.827032251] [listener_node]: I heard: "Hello World: 1"
...
```
::::