Docker is an open-source project that allows you to easily and quickly build, test, and deploy applications. Docker organizes software into containers that contain everything the software requires to run, such as libraries, system tools, code, and runtime. Docker allows you to quickly deploy and scale applications in any environment. Developers can use the development environments on Windows, Linux, or macOS.
In this tutorial, we learn how to install Docker CE on AlmaLinux 8. The steps are also applicable to Rocky Linux 8, CentOS 8, and REHL.
Step 1: Add Repository for Docker
You can add the official Docker CE repository to your AlamLinux 8 so that we can install it without having to manually download its packages. The repository can be installed with a single command.
$ sudo dnf config-manager --add-repo=https://download.docker.com/linux/centos/docker-ce.repo
Step 2: Run AlmaLinux/Rocky system Update
For the system to recognize the recently added Docker repository and the packages available in it, you must first run the system update, which will rebuild the AlmaLinux system repo cache.
$ sudo dnf update
You can look through the repository list to see if the newly added repo is there.
$ sudo dnf repolist -v
Step 3: Install Docker CE Engine on AlmaLinux 8 or Rocky Linux 8
Now that we've added the Docker repository to our system, we can install Docker-CE, as well as its command-line tool and containerd.io, to manage the container lifecycle of its host system using
$ sudo dnf install docker-ce docker-ce-cli containerd.io
Step 4: Start Docker
After the installation is complete, you may start the Docker service and set it to start automatically when the system boots up.
$ sudo systemctl start docker $ sudo systemctl enable docker
To check the docker service status, type:
$ systemctl status docker
Press q to exit back to command prompt.
Step 5: Execute Docker Commands without Sudo
By default, the docker command can only be run as the root user. To avoid requiring root access to run docker commands, you can add your current system user to the Docker group, allowing you to quickly run
docker command without prefixing it with sudo.
$ sudo usermod -aG docker $USER
Where $USER is the environment variable that contains your username.
Now, you can check if your user is in docker group or not.
You can change $USER in the above command with the specific system's user if you wish to give another user the privileges to manage Docker than the present one.
You can logout and log back in to get the group membership session updated.
Step 6: Verify Docker Installation
To verify the installation we can run a test container that will access and download an image from the Docker hub.
To verify docker installation, type:
$ docker container run hello-world
Docker initially checks locally for the hello-world image, if not found download the image from Docker Hub. Once the image is downloaded, the docker daemon created a new container from that image, and the application in the container is executed, to print the message.
Using Docker Commands
Let's check few basic commands of Docker. Run
docker info command to get information such as docker version installed, OS version, CPU, Kernel information, and more.
$ sudo docker info
To search images available on Docker Hub, use docker search followed by image name. For example to search ubuntu image, type:
$ docker search ubuntu
NAME DESCRIPTION STARS OFFICIAL AUTOMATED ubuntu Ubuntu is a Debian-based Linux operating sys… 12724 [OK] dorowu/ubuntu-desktop-lxde-vnc Docker image to provide HTML5 VNC interface … 563 [OK] websphere-liberty WebSphere Liberty multi-architecture images … 280 [OK] rastasheep/ubuntu-sshd Dockerized SSH service, built on top of offi… 255 [OK] consol/ubuntu-xfce-vnc Ubuntu container with "headless" VNC session… 241 [OK] ubuntu-upstart DEPRECATED, as is Upstart (find other proces… 113 [OK] 1and1internet/ubuntu-16-nginx-php-phpmyadmin-mysql-5 ubuntu-16-nginx-php-phpmyadmin-mysql-5 50 [OK] open-liberty Open Liberty multi-architecture images based… 48 [OK] ubuntu-debootstrap DEPRECATED; use "ubuntu" instead 44 [OK] i386/ubuntu Ubuntu is a Debian-based Linux operating sys… 25
Official column with
OK shows that image the original image supported by the company behind that project.
To download the official ubuntu image, type:
$ docker pull ubuntu
To display the downloaded images, type:
$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE ubuntu latest fb52e22af1b0 6 days ago 72.8MB hello-world latest d1165f221234 6 months ago 13.3kB
To run the ubuntu container, type:
$ docker run -it ubuntu
In this tutorial, we learned how to successfully install Docker in AlmaLinux 8. The steps mentioned for installing Docker are also applicable to Rocky Linux 8, CentOS 8, and RHEL.