12/12/2021

Linux Docker Version

78

Jun 29, 2020 Docker is a tool that is used to run software in a container. It’s a great way for developers and users to worry less about compatibility with an operating system and dependencies because the contained software should run identically on any system. Docker takes away repetitive, mundane configuration tasks and is used throughout the development lifecycle for fast, easy and portable application development - desktop and cloud. Docker’s comprehensive end to end platform includes UIs, CLIs, APIs and security that are engineered to work together across the entire application delivery lifecycle. $ docker -v the output is: Docker version 18.06.1-ce, build e68fc7a What version they mean when the write. If you use Docker 1.13 or higher, use -cpus instead. Asking because the difference between 18 and 1 is too big to me. Can the docu be so old? Or do the docker versions increase so fast?

What is a Docker Image

Docker images are a read-only template which is a base foundation to create a container from. We need an image to start the container. Ther are a lot of pre-built images out there on the docker hub. You can also have your own custom image built with the help of Dockerfile and the command “docker build”.

Searching a Docker Image

Linux docker version 9

To search an image on a Docker registry, run the following command.

Linux docker version 10

The search term can be anything like centos, if you want to search for a image having centos OS. For Example :

Here,
NAME : Is the name of the docker image.
DESCRIPTION : A short description on what the image is about.
STARS : How many people have liked the image.
OFFICIAL : Specifies whether the image is built from a trusted source.
AUTOMATED : Tells whether the images is built automatically with a push in GitHub or Bitbucket repositories.

You can combine more options here like number of minimum stars the image has and/or is the images has the AUTOMATED flag set to [OK]. For Example:

Check Docker Version Linux

Linux

To find more options and functionalities with “docker search” command, use the help option.

Pulling a Docker Image

To pull an image from the Docker registry, run the following command:

Linux

here,
NAME – The main group of images with similar role. For Example centos.
TAG – Image with a specific tag such as centos7.

For Example, to pull centos 6 image :

By default, if you do not specify the optional tag field in the above command, the image with the latest tag gets pulled. You can also pull all the images from a specific tag. For Example :

Listing Docker Images

Run the below command to list all the images available locally on the system:

Docker gains popularity in recent years as it solves many software development issues by containerizing the application. It allows us to ship the application together with all the dependencies that it needs in the machine in one container resolving the issue that it only works on certain machines. This guide will help you to install Docker on CentOS or in any RHEL based Linux machine. You can also follow our guide here on how to install CentOS 8 in a VirtualBox.

Linux Docker Version

Check the Prerequisites

First, check if centos-extras repo is enabled in your machine. Run the command below and you should see centos-extras in your repo list.

If you have an older version of Docker, uninstall it first. Otherwise, you can skip this step. To uninstall old docker, run the command below.

Add the Docker repository in your CentOS machine. To add, install the yum-utils first and then add the repo.

Install Docker on CentOS

Now that we have our prerequisites installed, we are now ready to setup Docker. First, we update the repository.

In case that you are getting an error that containerd.io conflicts with runc, or similar below,

Then, please try this command. This will remove conflicting podman and buildah:

Next, install Docker by running the command:

If you have successfully installed Docker, then you can skip this step and proceed to configure Docker section. Otherwise, if it fails that the docker-ce requires containerd.io version to be higher than a specific version, then you can fix this by installing the containerd.io manually. This happens when that specific version of containerd.io is not yet added to the CentOS repository. You might be seeing something like this:

To fix this, visit https://download.docker.com/linux/centos/7/x86_64/stable/Packages/ and check for the latest version of containerd.io. Get the link for containerd.io rpm file and install it using yum install. For example:

Then, install Docker again but this time, without containerd.io since we already installed it manually.

Configuring Docker

Docker is now installed but we still need to do some configurations. First, we need to add our user to the docker group. To check who is included in the docker group, run the below command:

If your user is not included, then we can add it using sudo usermod -a -G docker <username>. For example, using javapointers as username:

Then, let’s verify again if our user was now added in docker group.

Next, we will add the docker as a service to automatically starts at boot. We can add them using:

Restart your VM and finally, test it by running hello-world image. Open a terminal again and type:

And if you see something similar below, then you have successfully installed Docker on your CentOS or RHEL based machine.

Current Docker Version Linux

That’s it! Please let us know in the comments if this guide helps you or if there are issues you’ve encountered while following this guide.

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