How to Install Docker on Linux

Docker originates from a collection of “platform-as-a-service” products and services that deliver packages known as ‘containers’ through operating system virtualization technology. All the code, libraries, data, and configurations of an application, tool or service are packaged into a container. Similarly, containers are isolated from each other (and the underlying host system) but can still exchange data via standard protocols.

Docker is an open-source containerization technology that facilitates the development, testing, and deployment of applications in the form of self-contained containers and creates and manages containers for application development.

Docker is a modern platform for rapid development and innovation that is used to automate the deployment of applications in lightweight containers so that applications can run efficiently in different contexts. The runtime of a program is enclosed in a container that contains the software and hardware components necessary for the program to function.

Docker is widely used in today’s continuous integration and deployment (CI/CD) pipelines for software development and DevOps operations.

Containers have something in common with virtual machines, except that they can be moved more easily, use less system resources, and rely on the host operating system. As a result, Docker facilitates the management and execution of programs, which makes it possible to run programs independently of resource processes. In this article, we will teach you how to install Docker on Ubuntu, Debian, and CentOS operating systems step by step.

It’s worth mentioning that Docker is open-source software, which means it’s free to use, modify, improve, hack, and create new versions. If you are interested in using Docker features on popular Linux operating systems, this article describes installing Docker on Ubuntu 20.04 LTS, Debian 11, and CentOS 7 step by step. Follow us to easily benefit from Docker on Ubuntu, Debian, and CentOS.

Introducing Docker-related fixes

Docker container: a created instance of Docker images that runs along with applications. Each container has its own unique ID and is kept entirely separate from other containers. But the core of containers is the common feature between containers.

Docker Daemon: This is the term for the hidden process of the host system that creates and manages containers. It is also known as Docker Engine.

Docker Client: The user uses Docker Client, which is a command line tool to communicate with Docker Daemon.

Docker image: A screenshot file of a container that cannot be modified. The file system and application dependencies required to run the software are stored in a Docker image.

Docker registry: a program that oversees the distribution and storage of Docker container images. The Docker registry can make information available to the public or keep it private.

Advantages of Docker

• open source
• Freedom to use any technology to complete the work process
• Providing a light and organized environment to achieve the testing goals of the programmers
• A platform for rapid application development
• Speeding up the process of writing codes and executing them in an environment
• Providing the possibility of testing, sending, and deploying codes

Installing Docker on Ubuntu: Step by Step

prerequisites

Pay attention to the following things that are important to go through the steps of installing Docker on Ubuntu Linux:

• Launch and access non-root sudo user
• Ensure internet connection
• Configuration and initial setup of Ubuntu 20.04 Linux on the system

Note: If you plan to run Docker on a Linux server, set up a firewall in addition to the above. It should be noted that creating a user account in Docker Hub is also necessary.

In the standard repositories of Ubuntu 20.04, the Docker package is available for installation, but to ensure that we have installed the latest version of Docker, it is better to search for and install the newest version of Docker in the official Docker repositories.

Step 1: Installing Docker on the Ubuntu system is not complicated. First, you activate the Docker repository for legal and valid downloads by adding and installing the new package source and installing the GPG Docker key.

Step 2: First, update a list of packages:

sudo apt update

Step 3: Install the necessary prerequisites to add a new HTTPS repository:

sudo apt install apt-transport-https ca-certificates curl gnupg-agent software-properties-common

Step 4: In this step, using the curl command, we download the GPG key of the official Docker repository and add it to our system:

curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add –

Step 5: Through the following command, we add the Ubuntu stable version Docker repository to the list of APT sources:

sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"

Once the Docker repository is enabled, any Docker version found there can be installed.

Step 6: Docker installation on Ubuntu 20.04 will start. Follow the steps below to install the latest version of Docker on your system. Before beginning the installation process, it is better to update the list of available packages in the system. If you intend to install a specific version of Docker, skip this step and go to the next step.

sudo apt update

sudo apt install docker-ce docker-ce-cli containerd.io –y

Step 7: Before installing a particular version, you need to get a complete list of Docker repository versions and update them.

sudo apt update

apt list -a docker-ce

In the second column, you will see a list of current Docker releases. We see that the official Docker repository hosts a version of Docker (5:19.03.93-0ubuntu-focal).

Output

docker-ce/focal 5:19.03.9~3-0~ubuntu-focal amd64

To install a particular version of Docker, add =<VERSION> after the package name in the command:

sudo apt install docker-ce=<VERSION> docker-ce-cli=<VERSION> containerd.io

The Docker service starts immediately after the installation is completed to begin the activation process at boot. To ensure its execution, enter the following command:

sudo systemctl status docker

After entering the above command, you will get the following result, which indicates that the service is activated and running:

Output:

• docker.service - Docker Application Container Engine
  
  Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
  
  Active: active (running) since Thu 2020-05-21 14:47:34 UTC; 42s ago
  
  TriggeredBy: ● docker.socket
  
  Docs: https://docs.docker.com
  
  Main PID: 24321 (dockerd)
  
  Tasks: 8
  
  Memory: 46.4M
  
  CGroup: /system.slice/docker.service
  
  └─24321 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

If for any reason, you did not receive the Active message in the above command, that means your Docker is not running and use the following command to run it:

sudo systemctl start docker

You can set Docker to run automatically at system startup via the following command:

sudo systemctl enable docker

Also, use the following command to restart Docker:

sudo systemctl restart docker

Step 8: Once a new version of Docker is available, you can upgrade packages via the following standard method:

sudo apt update

 sudo apt upgrade

If you don’t want to update Docker packages, mark it as disabled:

sudo apt-mark hold docker-ce

The Docker command line application, commonly known as the Docker Client, is now included in standard Docker installation alongside the Docker service (daemon). In this guide, we will also mention Docker commands.

Run Docker commands as a non-root user

By default, Docker commands can be run by the root user with sudo privileges or by a user who is in the Docker group.

If you try to run Docker commands as a user that is not in the Docker group or without the sudo invocation, you will get the following results:

Output

docker: Cannot connect to the Docker daemon. Is the docker daemon running on this host?.

See 'docker run --help'.

So if you want to run Docker on Ubuntu without the need for sudo command and use a user other than root to run Docker commands, you need to add the user to the docker group. This group is automatically created when Docker CE is installed. To do this, follow the instructions below:

sudo usermod -aG docker ${USER}

$USER is the environment variable where your username is placed.

To update and refresh membership in the group, log out and log in again or enter the following command:

su - ${USER}

Now you can run docker commands as a non-root user without problems. If you do not go through the above steps, you must have sudo privileges to run docker commands and type sudo before each docker command.

Installation confirmation

To ensure the Docker installation is successful, we run a test container.

To test Docker, you can use the docker command without the need for the sudo prefix:

docker container run hello-world

A test image is received through this command, created by a container that displays the events related to the execution of this command by presenting the message “Hello world.”

Of course, at first, a local search is performed, and if the test image is not already on the local machine, a search is made in Docker Hub to find the image, and then it runs it in a container, outputs “Hello from Docker,” and terminates. The result is as follows:

Because there is no long-running process, the container stops after printing the message.

As you know, Docker containers are created based on Docker images. Docker automatically downloads images from Docker Hub. This cloud-based registry service can store Docker images in public or private repositories.

To check the local Docker images already available on the system, enter the following command:

docker images

To search for Docker images in Docker Hub, use the Search command. For example, if you want to search for Ubuntu images, type the following command:

docker search Ubuntu

Therefore, this command finds the list of images related to Ubuntu by searching in Docker Hub scripts.

Checking the installation status

You can also track the status of the Docker installation through the Sudo command, in which case you must enter the following command:

sudo docker version

As a result, you can get the Docker version you installed from the version field in the output you received.

Uninstalling Docker on Ubuntu

Before uninstalling Docker, it is better to delete images, networks, containers, and volumes.

If you want to stop a specific container that was created:

1. First, access a list of running containers via the following command:

docker container ls –a

2. Then in the NAMES column, find the desired container name.
3. Finally, delete the desired container using its name.

docker rm container_name

To stop all active containers and remove all docker objects, enter the following commands:

docker container stop $(docker container ls -aq)

docker system prune -a –volumes

Now you can uninstall docker with the apt command:

sudo apt purge docker-ce

sudo apt autoremove

Installing Docker on Debian 11 by following 14 steps

Prerequisites

• Having Sudo user privileges
• Having a 64-bit system
• Stable and secure connection to the network
• Configure Debian 11 on the system

Starting the Docker installation process on Debian 11

Step 1: Install Docker Dependencies

The first step to start the process of installing Docker on Debian 11 is to update the system. To do this, open a terminal using CTRL+ALT+T and enter the following command:

sudo apt-get update

Next, we use the following command to add the necessary Docker dependencies to the Debian platform:

sudo apt –y install apt-transport-https ca-certificates curl gnupg2 software-properties-common

Note that the Docker dependencies have been successfully installed so that the application will run without any problems.

Step 2: Add the GPG key of the official Docker repository

Before you set up the repository to receive and install Docker packages, you need to include the Docker GPG key in Keyrings. The main function of this key is to ensure the validity of downloaded Docker packages. Accomplish Docker’s GPG key target by running the following command:

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

Step 3: Adding the trusted repository

To get the most up-to-date docker packages, you should now add the stable repository with the following command. As a result, we will launch the repository.

Echo “deb [arch=amd64 signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/debian $(lsb_release –cs) stable” | sudo tee /etc/apt/sources.list.d/docker.list

Step 4: Update Package Cache

After adding a repository, you need to update the package cache with the latest information from the newly added repository. To do this, you must run the following apt command:

apt-get update

Step 5: Install Docker Engine

Then run the following command to get and install the latest Docker container and engine:

apt-get install docker-ce docker-ce-cli containerd.io

Step 6: Checking the Docker version

After you have installed the latest versions of the Docker engine and container, enter the following command to check the Docker version:

docker-version

Step 7: Check the Docker service status

After a successful installation, you should now check the status of the Docker run. To achieve our goal, we use the “systemctl” command. A system’s services can be managed with this command. Through the “status” option of the “systemctl” command, we check whether the Docker service is running on our Debian server or not:

sudo systemctl status docker

After executing the above command, if Docker runs, the word Active (Running) will be displayed in green.

After installation, the Docker service will start automatically. To ensure that the Docker service is running, you can use the systemctl status docker command that we explained earlier. If needed, the systemctl start docker and systemctl restart docker commands can be used to start and reactivate the docker service, respectively.

Step 8: Docker test

So far, we have successfully installed Docker on the Debian system and checked the status of the Docker service. We need to run the “Hello-World” global Docker container test sample to check Docker performance.

Run the Hello World image

You can build your first container using the docker engine and hello-world image. You can do this by issuing the hello-world command, as shown below:

docker run hello-world

Step 9: List Docker images

Type “docker images” at a command prompt to see a complete list of available images. The docker images and docker image commands may look similar, but they perform separate tasks. You can use the docker image <command> syntax if you want to manage your own Docker images. But here we are going to access a list of images. So run the following command:

docker images

Step 10: Run the Ubuntu container

At this point, you can start an Ubuntu Container with the docker run-it ubuntu bash command. If you do not specify a label for the image, the latest image for Ubuntu is used by default. If the image is not already available on your local system, the container will be created from an image downloaded from the Ubuntu library. For this purpose, run the following command:

docker run -it ubuntu bash

 

Step 11: List the docker container

Use the following command to list all containers of this software regardless of their current state:

docker ps-a

Step 12: Managing Docker containers

To initialize a container, the following command should be used:

docker start <container_id>

For example, if you wanted to launch a container with ID 5aa62402b888 for the Ubuntu Bash you created, you would run the following command:

docker start 5aa62402b888

And use the ps command to check the status of the container:

docker ps

Also, to stop running a specific container, use the following command:

docker stop <container_id>

For example, if you want to stop a container with the ID 5aa62402b888, you should put the real ID of the active container in the <container_id> field of the above command:

docker stop 5aa62402b888

Then, as we explained before, rerun the ps command to check the status:

docker ps

Also, run the following command to delete the image:

rm <container_id>

After removing the image, use the docker images command to check the list of images and ensure that the container with the specified ID is removed:

docker images

Step 13: Push the images to the Docker Hub repository

To use and save images in Docker Hub repositories, you must create a user account and enter the repository with the user account’s credentials. To create a Docker Hub account, visit the Docker Hub site and then type this command to access your account:

docker login

 

After executing the command, it is necessary to enter the username and password and press Enter.

After you have successfully logged in, push your images through the following command:

docker push <Image_name>

Note: The image may need to be tagged before being pushed to the Docker Hub repository.

Step 14: Uninstall Docker

If you want to remove the Docker engine, we must uninstall Docker Engine, CLI, and Containerd packers with the help of the following command:

apt-get remove docker-ce docker-ce-cli containerd.io

Note: Images, containers, volumes, and specialized configuration files on your host will not be removed without your intervention. Therefore, to manually delete all images, containers, and volumes, the following commands should be used:

sudo rm -rf /var/lib/docker

To remove containers, use the following command:

sudo rm -rf /var/lib/containerd

Steps to install Docker on CentOS

This tutorial will present the process of installing Docker on CentOS7. First, pay attention to the prerequisites:

prerequisites

• Having a user account with Sudo permission
• Using a supported version of CentOS, as Docker does not support or test older distributions.
• Activation of the CentOS Extras repository (usually, this repository is enabled by default in CentOS, if it is disabled, you must re-enable it.)
• Accessing the terminal by right-clicking on the desktop and selecting the Open in Terminal option
• Installing the yum software package manager

Start the Docker installation process on CentOS7 using Yum

To install Docker from Docker repositories on CentOS, using the Yum command is the easiest way.

Step 1: Update the Docker package database by running the following command:

Sudo yum check-update

You may have to wait a few minutes for the operation to complete.

Step 2: Install Dependencies

At this stage, install the necessary prerequisites for installing Docker on CentOS by typing the following command:

sudo yum install -y yum-utils device-mapper-persistent-data lvm2

The -y option in the Yum installer is to accept all defaults, which continues the installation process regardless of opening a window for confirmation, and this option also results in the addition of the yum-utils yum-config-manager switch. Docker requires the Device-Mapper-Persistent-Data and lvm2 packages to function correctly, as it depends on the Device Mapper storage driver.

Step 3: Adding Docker repository to CentOS

Adding a stable Docker CE repository to a CentOS system is a prerequisite for installing Docker edge or testing versions. For this purpose, enter the following command:

sudo yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo

The stable version includes fewer changes, and more time and precision are spent on testing it. It also has a slow update cycle. While Edge versions are updated more often, stability tests are not performed on them.

Note: It should be noted that activation of additional repositories is not required for stable versions because when installing Docker if the desired version is not specified, the latest version of Docker will be selected by default. Enabling the stable repository prevents accidental updates from the stable version to the edge version.

Step 4: Using Yum to install Docker on CentOS

After going through the previous steps, you can now install Docker on CentOS7 with the help of the following command:

sudo yum install Docker

The installation process will start automatically. Upon completion, a message will appear informing you that Docker has been successfully installed and what version of Docker is currently running on your system.

Depending on your operating system, you may be prompted to accept the GPG key. Doing this works like a digital fingerprint.

The following format should be used for fingerprints:

060A 61C5 1B55 8A7F 742B 77AA C52F EB6B 621E 9F35

Step 5: Managing the Docker service

We will not see the CentOS service running by installing Docker on CentOS. To run the service, we need to set it so that when the system starts, the Docker service is also started automatically. Therefore, it is necessary to execute the following instructions in order.

Start Docker:

sudo systemctl start docker

Enable Docker:

sudo systemctl enable docker

Check service status:

sudo systemctl status docker

Seeing the word Active (Running) in green indicates that Docker is active.

Installing a specific version of Docker on CentOS

If you wish to set up a certain Docker version. First of all, you should make a list of the available versions. So run the following command:

yum list docker-ce --showduplicates | sort-r

The above command will result in a list of versions in the repositories activated in the previous steps. To install a specific version of Docker, enter the following command:

sudo yum install docker-ce-<VERSION STRING>

To find the <VERSION STRING> field, pay attention to the middle column, the first part of the alphanumeric code, before the hyphen.

Other docker commands that we explained about Ubuntu and Debian, such as the docker “Hello World” command to check docker performance and docker images to check all the images in the system, docker search [search] to search for images in the docker repository, docker pull [image_name] for To download the desired image, docker run -t -i [image_id or image_name] to call the image using its ID or name (the –i option to make the image interactive and the –t option to access the terminal), etc., are also applicable for CentOS.

FAQ

Conclusion

Docker is one of the most popular and modern open-source platforms for developing, testing, and rapidly producing applications among programmers. Docker has become an essential tool for developers with its ability to simplify the creation, distribution, and testing of code and its important role in bringing together the components necessary to run an application on any platform.

In this article, we have explained how to install Docker in Ubuntu, Debian, and CentOS comprehensively and in simple language, and you were able to benefit from the features of Docker on Debian, Ubuntu, and CentOS systems. (Docker’s official documentation can guide you further) Installing Docker on popular Linux operating systems allows you to take steps toward your career success using a few commands.

Also, running Docker on a Linux virtual server offers special benefits such as more control over server resources, better performance, and easier management. So don’t neglect running Docker on a Linux VPS because it’s a smart choice. If you plan to run Docker on a Linux virtual server, you must first purchase the Desired Linux VPS from a reputable company; choosing the ideal Linux VPS is effective in improving the security and performance of containers, and then configure and run your desired operating system on the server by following the initial setup instructions. Fortunately, the steps to install Docker on the server are the same as those we taught in this article, so don’t worry about installing Docker on a Linux VPS with Ubuntu, Debian, and CentOS operating systems. We hope this article is useful for you; If you have any questions or need help with installing Docker on Linux operating systems, let us know in the comments section.