Welcome to our guide on how to install and use docker ce on CentOS 8. Docker is a platform that enables developers and system administrators to build, run, and share applications with containers.
The exits two editions of docker available.
Docker CE and
- Docker CE (Community Edition) is the open-source, community supported version of Docker and is available for free.
- Docker EE (Enterprise Edition) is a commercial/premium version of Docker CE and is supported by Docker Inc.
There are different methods in which you can install Docker CE on CentOS 8;
- Installing Docker CE on CentOS 8 from Docker Repositories
- Installing Docker CE manually on CentOS 8 using the RPM binary package
- Installing Docker CE using Docker Installation Script (Beyond the scope of this tutorial).
Installing Docker CE on CentOS 8 from Docker Repositories
Run System Update
Ensure that your system package cache is up-to-date.
Uninstall Docker Versions
If any of the old docker versions are installed on your system, ensure that you remove them and their dependencies before you proceed.
dnf remove docker*
Install Docker CE Repository on CentOS 8
To ensure seamless future upgrades of Docker packages, you can install it from their official repos. For this, you need to setup the Docker repositories on CentOS 8 by executing the command below;
dnf config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
The command above installs and enable Docker CE repo on CentOS 8.
Install Docker Engine (Docker CE) on CentOS 8
Once the repos are in place, proceed to install docker-ce and other tools including
containerd.io, an open and reliable container runtime on CentOS 8.
Next, install Docker CE and Docker CE CLI utility.
dnf install docker-ce docker-ce-cli containerd.io
Installing Docker CE from an RPM package
You can as well install Docker ce on CentOS 8 using an RPM package.
Download the latest versions of the individual packages installed above from Docker Packages page.
for i in containerd.io-1.4.6-3.1.el8.x86_64.rpm docker-ce-20.10.7-3.el8.x86_64.rpm docker-ce-cli-20.10.7-3.el8.x86_64.rpm; do dnf install -y https://download.docker.com/linux/centos/8/x86_64/stable/Packages/$i; done
Replace the version/release numbers of the packages accordingly.
Starting Docker Service
To start and enable Docker and Containerd service to run on system boot;
systemctl enable --now docker containerd
If you run Docker as standard user, you may get such an error;
[[email protected] ~]$ docker ps -a
docker: Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: ... /var/run/docker.sock: connect: permission denied. See 'docker run --help'.
Therefore, if you need to run docker as non-root user, simply add the user you want to run docker as to docker group or simply, grant the user sudo rights. For example to add a user,
usermod -aG docker koromicha
koromicha : koromicha docker
Next, log out and login again as the non root user that you added to the docker group so that your group membership can be re-evaluated.
You can then run docker as a non root user.
Verifying Docker CE installation
Check the docker version;
Docker version 19.03.12, build 48a66213fe
To verify that Docker CE is running well, you can try running the
hello-world container image.
[[email protected] ~]$ docker run hello-world
Unable to find image 'hello-world:latest' locally latest: Pulling from library/hello-world 0e03bdcc26d7: Pull complete Digest: sha256:8e3114318a995a1ee497790535e7b88365222a21771ae7e53687ad76563e8e76 Status: Downloaded newer image for hello-world:latest Hello from Docker! This message shows that your installation appears to be working correctly. To generate this message, Docker took the following steps: 1. The Docker client contacted the Docker daemon. 2. The Docker daemon pulled the "hello-world" image from the Docker Hub. (amd64) 3. The Docker daemon created a new container from that image which runs the executable that produces the output you are currently reading. 4. The Docker daemon streamed that output to the Docker client, which sent it to your terminal. To try something more ambitious, you can run an Ubuntu container with: $ docker run -it ubuntu bash Share images, automate workflows, and more with a free Docker ID: https://hub.docker.com/ For more examples and ideas, visit: https://docs.docker.com/get-started/
To list running containers;
[[email protected] ~]$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 4083300e3660 hello-world "/hello" 3 minutes ago Exited (0) 5 minutes ago laughing_visvesvaraya
While verifying docker installation above, we ran the hello-world docker container image. Building and running docker containerized applications is the next step after setting up your docker environment.
So there are two things here: You can either build and run your own docker container images or pull already created and shared images from docker hub, an image repository for Docker images.
In this demo, we will learn how to use already created docker images from docker hub. With docker command, you can easily pull docker images from docker hub, as we did with the hello-world image above.
If you want to build your own images and share on docker hub, then you need to sign up to create your own namespace for storing your images, which then can be publicly available.
docker command has quite a number of command line options for running various tasks.
The command line syntax is;
docker [OPTIONS] COMMAND
You can view various command options and commands by executing;
... Options: --config string Location of client config files (default "/home/koromicha/.docker") -c, --context string Name of the context to use to connect to the daemon (overrides DOCKER_HOST env var and default context set with "docker context use") -D, --debug Enable debug mode ... Management Commands: builder Manage builds config Manage Docker configs container Manage containers ... Commands: attach Attach local standard input, output, and error streams to a running container build Build an image from a Dockerfile commit Create a new image from a container's changes cp Copy files/folders between a container and the local filesystem create Create a new container ...
To view help for a specific docker command;
docker COMMAND --help
For example, to find the usage of docker
docker run --help
You can search for the specific publicly available Docker images on Docker Hub using
docker search command. The docker search command syntax is;
docker search [OPTIONS] TERM
docker search --help to see more options.
For example, to search all the images containing the term hello-world;
docker search hello-world
NAME DESCRIPTION STARS OFFICIAL AUTOMATED hello-world Hello World! (an example of minimal Dockeriz… 1226 [OK] kitematic/hello-world-nginx A light-weight nginx container that demonstr… 147 tutum/hello-world Image to test docker deployments. Has Apache… 72 [OK] dockercloud/hello-world Hello World! 19 [OK] ...
Some column headings are self explanatory. Other columns include;
- STARS : Shows the number of likes the image has had.
- OFFICIAL : Specifies whether the image is built from a trusted source.
- AUTOMATED : Shows whether the image has been automatically build from source code in an external repository and automatically pushed to Docker repositories.
Usually, an image with no prefix is considered official docker hub image, stable and being maintained. It also contains [OK] on the Official column.
Once you have identified the image that you need to run, you can either pull it and store it on your local registry using the the
docker pull command or simply run it using
docker run command.
For example, to search and pull an Ubuntu system docker image;
docker search ubuntu
NAME DESCRIPTION STARS OFFICIAL AUTOMATED ubuntu Ubuntu is a Debian-based Linux operating sys… 11046 [OK] dorowu/ubuntu-desktop-lxde-vnc Docker image to provide HTML5 VNC interface … 441 [OK] rastasheep/ubuntu-sshd ...
Let us pull the official Ubuntu image.
docker pull ubuntu
This will by default pull the most recent version of Ubuntu currently available, usually the latest LTS versions.
Using default tag: latest latest: Pulling from library/ubuntu a4a2a29f9ba4: Pull complete 127c9761dcba: Pull complete d13bf203e905: Pull complete 4039240d2e0b: Pull complete Digest: sha256:35c4a2c15539c6c1e4e5fa4e554dac323ad0107d8eb5c582d6ff386b383b7dce Status: Downloaded newer image for ubuntu:latest docker.io/library/ubuntu:latest
You can specify other tags for specific types of Ubuntu though;
docker search ubuntu:20.04
You can list locally available images using
docker images command.
REPOSITORY TAG IMAGE ID CREATED SIZE ubuntu latest 74435f89ab78 11 days ago 73.9MB hello-world latest bf756fb1ae65 5 months ago 13.3kB
Once you have pulled a container from Docker hub and is available locally, you can either run it with
docker run or
docker create command.
docker run, you can create a container, start it and access it using a shell to run any command inside it. The docker run command line syntax is;
Usage: docker run [OPTIONS] IMAGE [COMMAND] [ARG…]
For example, to run our Ubuntu image we pulled from Docker hub above in an interactive manner (option -i) drop to the shell (option -t, to allocate pseudo-TTY);
docker run -it ubuntu
This drops to the shell;
You are now inside an Ubuntu container, with a container ID, 43ff7a031a0b, as root user. Anything that you run or execute under this shell happens within the filesystem of the container itself.
You can execute the commands directly without dropping to container shell;
docker run ubuntu cat /etc/os-release
NAME="Ubuntu" VERSION="20.04 LTS (Focal Fossa)" ID=ubuntu ID_LIKE=debian PRETTY_NAME="Ubuntu 20.04 LTS" VERSION_ID="20.04" HOME_URL="https://www.ubuntu.com/" SUPPORT_URL="https://help.ubuntu.com/" BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/" PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy" VERSION_CODENAME=focal UBUNTU_CODENAME=focal
If you run the container interactively and started a shell, you can run your commands inside it.
When you exit the shell, the shell attached to the container is detached and container stops. If you used the options, -i and -t when running docker container, you can exit the shell without stopping the container, use the keystrokes
Ctrl + p then
Ctrl + q.
You can as well run container in background and print container ID
docker run -dit --name ubuntudemo ubuntu
To attach it to the console;
docker attach ubuntudemo
You can list live (currently running) containers using
docker ps command.
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 1c280cf21322 ubuntu "/bin/bash" 2 minutes ago Up 2 minutes ubuntudemo
To list all containers, those running and those exited;
docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 1c280cf21322 ubuntu "/bin/bash" 3 minutes ago Up 3 minutes ubuntudemo b5453d11a544 ubuntu "/bin/bash" 10 minutes ago Exited (0) 8 minutes ago stupefied_hawking a65d1797c504 ubuntu "/bin/bash" 14 minutes ago Exited (0) 12 minutes ago zen_ramanujan c4d68a2b1b39 ubuntu "/bin/bash" 23 minutes ago Exited (137) 20 minutes ago sweet_dirac 9b7867c1daad ubuntu "cat /etc/os-release" 40 minutes ago Exited (0) 40 minutes ago great_allen
You can start exited/stopped containers using
docker start command. For example, to start container named, stupefied_hawking, with an ID of b5453d11a544, run the command;
docker start stupefied_hawking
docker start b5453d11a544
Similarly, you can stop a running docker using its name or container ID with
docker stop command.
docker stop ubuntudemo
Once you are done with your containers, you can remove them using
docker rm command.
To remove a stopped container with an ID of 9b7867c1daad, for example, in our
docker ps -a output above;
docker rm 9b7867c1daad
You cannot remove a running container unless you force the removal using using
--force option of docker rm command.
docker rm 1c280cf21322 -f
Docker images can as well be removed using
docker rmi command. For example, you can list images and get the image ID of the specific image you want to remove;
docker images -a
You can show numeric IDS using
docker images -a -q
Delete an image;
docker rmi 74435f89ab78
Or use the name repo name;
docker rmi ubuntu
--force to force the deletion.
That concludes our guide on how to install and use Docker CE on CentOS 8.