Installing Docker Engine.

You first need to set up a repository for first-time usage. You can subsequently install and update Docker from the repository

Setting up a repository

Update apt package index.
```
sudo apt-get update
```

Install packages to allow apt to use a repository over HTTPS.

sudo apt-get install \
 ca-certificates \
 curl \
 gnupg \
 lsb-release

Add Docker’s official GPG key:

sudo mkdir -p /etc/apt/keyrings

then:

curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg

Setup the repository

echo \
"deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu \
$(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

Install Docker Engine

Update apt package index:
```
sudo apt-get update
```

Install the latest version of Docker:

sudo apt-get install docker-ce docker-ce-cli containerd.io docker-compose-plugin

Make sure the engine is running: sudo docker run hello-world.

Note: This command downloads a test image and runs it in a container. When the container runs, it prints a message and exits as shown below.

Welldone, Docker Engine is installed and running.

Running as a rootless user

Requirements

Rootless mode allows running the Docker daemon and containers as a non-root user to mitigate potential vulnerabilities in the daemon and the container runtime.

Open a terminal ( CTRL + ALT + T )
Install dbus-user-session

(Simple Interprocess Messaging system) used for sending messages between applications.

sudo apt-get install -y dbus-user-session

Run:
```
dockerd-rootless-setuptool.sh install
```
This sets up the daemon. Make sure the system-wide docker daemon is not running. If so, kill the process using:
```
sudo systemctl disable --now docker.service docker.socket
```
Your output should be similar to the one in the image below.

If you get an error, if dockerd-rootless-setuptool.sh is not present, you may need to install the docker-ce-rootless-extras package manually

sudo apt-get install -y docker-ce-rootless-extras

Set up the environmental variables

export PATH=/usr/bin:$PATH
export DOCKER_HOST=unix:///run/user/1000/docker.sock

Setting up the client

Note. Use systemctl --user to manage the lifecycle of the daemon:
systemctl --user start docker
Alternatives

You must specify either the socket path or the CLI context explicitly. a. To specify the socket path using $DOCKER_HOST:
```
export DOCKER_HOST=unix://$XDG_RUNTIME_DIR/docker.sock
```
b. To specify the CLI context using docker context:
```
docker context use rootless
```

Run a Nginx open-source in a Docker container:

docker run -d -p 8080:80 --name nginx_server nginx

The -d option specifies that the container runs in detached mode: the container continues to run until stopped but does not respond to commands run on the command line.
The -p (alternative--publish) flag exposes the port outside of Docker, to make the port available outside of Docker. See Networking in containers
You can assign memorable names to your docker containers when you run them, using the --name flag. Here we choose nginx_server The first port number is associated with the host running the container. In the nginx example, 8080 is exposed on the host; in our case, that would be localhost:8080.
Now our Nginx is up and running. Verify Either on in your browser or in the terminal using the command below:
- Terminal:
```
curl http://localhost:8080
```

In a Browser. Open a new tab and navigate to:
```
http://localhost:8080
```

Shutting down a container. We aliased our container with the name nginx_server. Shutdown the container using:
```
docker stop nginx_server
```
Removing the container:
```
docker rm -f nginx_server
```
Shutdown all docker containers:
```
systemctl stop docker
```

Useful reference

Learn more at Docker docs
Using port mappings

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