Table of Contents
Confirming Docker Is Ready to Use
After installing Docker, you should verify that it is correctly installed and that the Docker Engine is running. This gives you confidence that you can proceed with the rest of the course without unexpected setup problems.
Checking the Docker Version
The first and simplest test is to ask Docker which version is installed. Open your terminal or command prompt and run the version command. If the installation was successful, Docker will print out information about the client and often the server.
On systems where the Docker command is docker, use that directly. On some older Windows setups you might see docker.exe, but in practice you still type docker.
If the version command prints version numbers and build information instead of an error, Docker is at least installed and the CLI is working.
If you see an error like "command not found" or "docker: command not found", your system does not recognize the Docker command. This usually means Docker is not installed, the installation failed, or the executable is not on your system PATH.
Ensuring the Docker Daemon Is Running
Having the Docker command available is not enough. Docker relies on a background service, often called the Docker daemon or Docker Engine, that must be running.
On graphical environments such as Docker Desktop, you can usually see an icon in the system tray or menu bar that indicates whether Docker is starting, running, or stopped. Wait until it shows that Docker is running before trying to use containers.
From the command line, you can indirectly test the daemon by running any command that talks to it. The version command with a specific flag that asks for server information is a common choice. If the daemon is running, you will see both client and server details. If the daemon is not running, you may see errors that say Docker cannot connect to the daemon or that permission is denied.
Errors like "Cannot connect to the Docker daemon" or "Is the docker daemon running?" mean that the background service is not active or you do not have permission to talk to it. Start Docker or adjust your user permissions, then try again.
Running the `hello-world` Test Image
The most common way to verify that Docker can pull and run containers is to start a tiny test container called hello-world. This image is specifically designed as a sanity check.
When you run the hello world container for the first time, Docker will:
- Connect to the default registry.
- Download the
hello-worldimage. - Create a container from it.
- Run the container, which prints a short message.
- Stop the container after it prints the message.
If this completes successfully, you will see a friendly message explaining that your installation appears to be working. This verifies several important things at once: the Docker CLI works, the daemon is running, networking to the registry is working, images can be pulled to your machine, and containers can be created and executed.
If the hello world test fails because the image cannot be pulled, you may have network issues or a problem accessing the default registry. If it fails with a daemon error, the Docker Engine may not be running or may require elevated privileges.
Confirming Basic Commands Work
Beyond the hello world test, it is useful to confirm that you can list images and containers without errors. Listing images shows whether the hello-world image has been downloaded to your system. Listing containers shows that the container that ran is recorded in Docker’s history.
You do not need to understand every detail of these outputs at this stage. The key point is to confirm that the commands return sensible information and do not report connection errors or permission problems.
If you see the hello-world image when listing images, and you see at least one container entry associated with it, your installation is functioning well enough to continue to the next part of the course.
Verifying Permissions and Access
On some systems, especially Linux, you might need special privileges to talk to the Docker daemon. If you find that Docker commands only work when you run them with elevated privileges, but not with your regular user, then your installation is partially working, but your user account is not configured to access Docker directly.
This is not strictly an installation failure, but it affects your day to day usage. It is a good idea to resolve this early so you do not have to rely on elevated privileges for every command. You will typically need to add your user to a specific group and then log out and back in, or follow your platform’s recommended procedure.
If Docker works only with elevated privileges, remember that running development tools with more permissions than necessary can introduce security risks. Aim to configure your user account so regular Docker commands work without extra privileges.
What Successful Verification Looks Like
By the end of this verification step, you should be able to:
See Docker’s version information without connection errors.
Run the hello world test container and read its success message.
List images and containers and observe entries corresponding to the test run.
Use Docker commands as your normal user account, or at least understand the permission setup on your system.
If you achieve all of these, your Docker environment is ready for practical work, and you can proceed with confidence to running and managing real containers.