How to Install Docker on Ubuntu – Step-by-Step Guide ~ Prasad Chenikkala

Step 1 — Installing Docker

The Docker installation package available in the official Ubuntu repository may not be the latest version. To ensure we get the latest version, we’ll install Docker from the official Docker repository.

The command sudo apt install apt-transport-https ca-certificates curl software-properties-common is used on Debian-based Linux distributions (like Ubuntu) to install several essential packages

Add a new software repository that uses HTTPS: This command ensures apt can securely communicate with that repository and verify its identity.

Install software from a source that requires curl for setup: Many third-party instructions rely on curl for initial downloads.
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Easily manage new APT repositories: software-properties-common provides the tools to streamline the addition of external software sources.

The Purpose of GPG Keys in APT Repositories

When you install software on a Debian-based system (like Ubuntu) using apt, the package manager relies on a system of trust to ensure that the packages you download are legitimate and haven't been tampered with. This trust is established through GPG (GNU Privacy Guard) keys

curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg

Add the Docker repository to APT sources:

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

Update your existing list of packages again for the addition to be recognized:

Sudo apt Update