Running a Docker Container

First, let’s check your Docker version to make sure everything is set up correctly:

docker version

You should see information about the client and server, like this:

Client:
 Version: 28.4.0
 OS/Arch: windows/amd64

Server:
 Version: 28.4.0
 OS/Arch: linux/amd64

This shows that Docker is installed and ready.

Now, let’s try running a simple container. Type this command in your terminal:

docker container run alpine echo "Hello World"

The first time you run it, you might see something like this:

Unable to find image 'alpine:latest' locally
latest: Pulling from library/alpine
Digest: sha256:4b7ce07002c69e8f3d704a9c5d6fd3053be500b7f1c69fc0d80990c2ad8dd412
Status: Downloaded newer image for alpine:latest
Hello World

Unable to find image means Docker doesn’t have this image on your computer yet.
Docker will download it from the internet (Docker Hub) automatically.
Finally, it runs the echo "Hello World" command inside the container.

If you run the same command again you will only see:

docker container run alpine echo "Hello World"

Hello World

This is because Docker now uses the image stored locally, so no download is needed.

Understanding the Command

The command we typed has several parts:

docker          container       run          alpine       echo "Hello World"
 |                 |             |             |                 |
Docker CLI       context       action        image        command inside container

docker – the Docker program we are using.
container – tells Docker we want to work with containers.
run – the action we want: start a new container.
alpine – the container image we want to use.
echo “Hello World” – the command that runs inside the container.

Let’s use a different image, like ubuntu, and run a small task:

docker container run ubuntu uname -a

Output might look like this:

Unable to find image 'ubuntu:latest' locally
latest: Pulling from library/ubuntu
Digest: sha256:c35e29c9450151419d9448b0fd75374fec4fff364a27f176fb458d472dfc9e54
Status: Downloaded newer image for ubuntu:latest
Linux 19b1c02e6d4e 6.6.87.2-microsoft-standard-WSL2 #1 SMP PREEMPT_DYNAMIC Thu Jun  5 18:30:46 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux

Here:

ubuntu is the image.
uname -a runs a command inside the container that shows system information.

Key Points About Images and Tags

Each container image has a version, called a tag.
If you don’t specify a tag, Docker uses latest by default.
The first time you use an image, Docker downloads it. Later runs are faster because the image is stored locally.

Sometimes you want a container to run without showing output in the terminal. Use:

docker container run -d --name my_ubuntu ubuntu sleep 60

-d: run in the background (detached mode).
--name: give the container a specific name (my_ubuntu).

Check the container status:

docker container ls -l   # shows last container status
docker rm -f my_ubuntu   # stops and removes the container

This setup lets you experiment with different images and commands easily, and is the basis for learning Docker containers.