Docker installation: Engine, Desktop, and Linux setup

This is an instruction of installation Docker on CentOS 7.

Adding the Docker repository

We should download the repository file https://download.docker.com/linux/centos/docker-ce.repo and put it into /etc/yum.repos.d/.

Also, we can do it in a more automatic way using yum-config-manager.

Install the yum-utils package (which provides the yum-config-manager utility) and set up the repository.

sudo yum install -y yum-utils

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

Installing Docker

The Docker Engine package is called docker-ce.

sudo yum install docker-ce

Package docker-ce-cli will be installed as a dependency.

sudo systemctl start docker

sudo systemctl enable docker

Also, we can install Docker Compose:

sudo yum install docker-compose-plugin

Check installation

sudo docker version

It shows a version of a client and server. Also, it shows a version of Go’s language, that was used during compilation.

Example:

Client: Docker Engine - Community
 Version:           20.10.17
 API version:       1.41
 Go version:        go1.17.11
 Git commit:        100c701
 Built:             Mon Jun  6 23:05:12 2022
 OS/Arch:           linux/amd64
 Context:           default
 Experimental:      true

Server: Docker Engine - Community
 Engine:
  Version:          20.10.17
  API version:      1.41 (minimum version 1.12)
  Go version:       go1.17.11
  Git commit:       a89b842
  Built:            Mon Jun  6 23:03:33 2022
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.6.6
  GitCommit:        10c12954828e7c7c9b6e0ea9b0c02b01407d3ae1
 runc:
  Version:          1.1.2
  GitCommit:        v1.1.2-0-ga916309
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

Another way to check installation is to run some container:

sudo docker container run hello-world

Manage Docker without sudo

The Docker daemon binds to a Unix socket instead of a TCP port. By default, that Unix socket is owned by the user root and other users can only access it using sudo.

If you don’t want to preface the docker command with sudo, add users to the group docker. When the Docker daemon starts, it creates a Unix socket accessible by members of the docker group.

sudo usermod -aG docker andrew

Restart Docker:

sudo systemctl restart docker

Log out and log back in so that your group membership is re-evaluated.

Verify that everything works without sudo:

docker run hello-world

Starting the Docker daemon

The Docker daemon (dockerd) creates, runs, and monitors containers and stores images. On most Linux systems systemd starts it for you:

sudo systemctl start docker

Enable it at boot:

sudo systemctl enable docker

You can also run docker daemon directly, but systemd is the usual approach.

Changing the storage driver

Restart the daemon with a different storage driver if the kernel supports it:

docker daemon -s overlay

Use --graph or -g to set Docker’s root directory — sometimes required so storage sits on the right filesystem (for example docker daemon -s btrfs -g /mnt/btrfs_partition).

To make the change permanent, edit the service unit or defaults file for your distro (on older Ubuntu, DOCKER_OPTS in /etc/default/docker).

See Storage drivers for driver trade-offs.

SELinux on Red Hat systems

On RHEL, CentOS, or Fedora, SELinux may block Docker with opaque Permission denied errors.

Check the mode:

sestatus

If Current mode is enforcing, switch to permissive mode (logs violations but does not block):

sudo setenforce 0

For production, configure SELinux policies for Docker instead of leaving enforcing disabled permanently.