How to Install Docker on CentOS 7 Linux systems
In this article, I’ll show you how to install Docker in CentOS 7 Linux system. This is your first step to get started with Docker engine on CentOS 7. I’ll use a minimal installation of CentOS 7 64bit to install Docker on it, of course the following installation steps are valid for all CentOS 7 installation types “Server without Gui, Server with Gui, minimal, etc..”.
On this machine we will install Docker engine, allowing you to run a docker image (container) within docker engine.
Introduction to Docker.
Docker is an open-source tool that makes creating & managing Linux containers(LXC) easy. Containers are like lightweight VMs which can be started & stopped in milliseconds. Dockers help the system administrators & coders to develop their application in a container and can further scale up to 1000 of nodes. Working with Docker containers adds many benefits for developers: better separation of application and the server configuration.
The main difference between container and VM(Virtual machine) is that dockers provide process based isolation , whereas VM provides full isolation of resources. Virtual machine takes a minute to start where as container can be started in a second or less than a second. Container uses the Kernel of host OS , whereas VM uses the separate Kernel. Container uses less disk space and memory than VM.
Docker requires a 64-bit OS and version 3.10 or higher of the Linux kernel. So, we need to check these two requirements against our CentOS 7 server.
To check your current kernel version and OS architecture, run the following command:
# uname -r 3.18.44-20.el7.x86_64
Perfect, our server is has the prerequisites for installing Docker. Let’s start our steps for installing Docker.
As you see, Docker Repository exists.
Hints: 1. If you want normal user to use docker, you need to add this normal user to the docker group. 2. By adding a user to the docker group, you'll have a full privileges on different docker commands, See the following optional step.
Step 5: Running Docker with Normal User Privileges “Optional”
You need to add your normal user to the docker group created by default when we installed the Docker packages. Here’s I’ll add user “msemari” to docker group:
# usermod -aG docker msemari
Now, logout and login again using this user “your normal user” and enjoy playing with Docker.
Extra Step: Removing Docker from your System
- List the installed Docker packages.
# yum list installed | grep docker docker-engine.x86_64 1.12.3-1.el7.centos @dockerrepo docker-engine-selinux.noarch 1.12.3-1.el7.centos @dockerrepo
- Remove the package.
# yum -y remove docker-engine.x86_64 # yum -y remove docker-engine-selinux.noarch
This command does not remove images, containers, volumes, or user-created configuration files on your host.
- To delete all images, containers, and volumes, run the following command:
# rm -rf /var/lib/docker
- Locate and delete any user-created configuration files.
I think, Docker if the future replacement of the VMs as it’s a lightweight server, it do not need a dedicated memory or disk or CPU power. Your server can run number of containers higher than the number of VMs with same server’s hardware. Personally, I’m moving from using VMs to use Docker containers to save my machines resources. Finally, with help of this article you could install Docker engine and enable, start it. I also included how to completely remove Docker packages.
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