Install Docker on CentOS 7/RHEL7
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 admin & coders to develop their application in a container and can further scale up to 1000 of nodes.

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.

One of the limitation of Docker is that it can be used only on 64bit hosts OS.

Installation of Docker on CentOS 7

Docker package is included in the default CentOS-Extras repository. So to install docker , simply run below yum command :

[root@localhost ~]# yum install docker

Start the Docker Service

Once the Installation is finished , start docker service and enable it at boot using below commands

[root@localhost ~]# service docker start
[root@localhost ~]# chkconfig docker on

Download the official Centos images Locally

[root@localhost ~]# docker pull centos
Pulling repository centos
192178b11d36: Download complete 
70441cac1ed5: Download complete 
ae0c2d0bdc10: Download complete 
511136ea3c5a: Download complete 
5b12ef8fd570: Download complete

 Verify CentOS images that have been fetched :

[root@localhost ~]# docker images centos
REPOSITORY          TAG                 IMAGE ID            CREATED             VIRTUAL SIZE
centos                         centos5             192178b11d36        2 weeks ago         466.9 MB
centos                         centos6             70441cac1ed5        2 weeks ago         215.8 MB
centos                         centos7             ae0c2d0bdc10        2 weeks ago         224 MB
centos                          latest              ae0c2d0bdc10        2 weeks ago         224 MB

Run a Docker Container :

[root@localhost ~]# docker run -i -t centos /bin/bash

[root@dbf66395436d /]#

As we can see centos container has been started and we got the bash shell. In docker command we have used options like ‘-i attaches stdin and stdout’ and ‘-t allocates a terminal or console’ . To disconnect from container type exit .

[root@cd05639b3f5c /]# cat /etc/redhat-release 
CentOS Linux release 7.0.1406 (Core) 

We can also search Containers based on fedora & ubuntu OS.

[root@localhost ~]# docker search ubuntu
[root@localhost ~]# docker search fedora

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