Docker is an open-source tool that automates the deployment of applications inside software containers by providing an additional layer of abstraction of operating system level virtualization on Linux. Docker makes it easier to create, deploy and run applications by using containers. Containers allow a developer to package up an application with all of the libraries and dependencies, and ship it all out as one package. Docker is same as virtual machine, rather than creating a whole virtual operating system. Docker allows applications to use the same Linux kernel as the system that they are running on. This gives a significant performance boost and reduces the size of the application.
Docker is preferred by many system admins and developers to maximize their creativity in an App production environment. For system admins, Docker gives flexibility and reduces the number of systems needed because of its small footprint and lower overhead.
In this tutorial, We’ll learn how to install Docker on CentOS-7.
##Requirements
CentOS-7 64-bit configured with static IP address. Kernel version must be 3.10 at minimum.
##Installing Docker
It is recommended to update your system before installing docker.
To update the system, Run:
sudo yum -y update
Docker package is not available in CentOS-7 repository. So you need to create repo for docker.
You can create docker repo by creating docker.repo file inside /etc/yum.repos.d/ directory.
sudo nano /etc/yum.repos.d/docker.repo
Add the following line:
[dockerrepo]
name=Docker Repository
baseurl=https://yum.dockerproject.org/repo/main/centos/7
enabled=1
gpgcheck=1
gpgkey=https://yum.dockerproject.org/gpg
After creating docker repo, run the following command to install docker.
sudo yum install docker-engine
Once docker has been installed, it is recommended to start docker service and set docker service to start at boot.
You can do this by running the following command:
sudo systemctl start docker.service sudo systemctl enable docker.service
You can check the status of Docker by running the following command:
sudo systemctl status docker.service
Finally, you can verify that the latest version of docker is installed with the following command
sudo docker version
You can see the output some thing like this:
Client:
Version: 1.10.0
API version: 1.22
Go version: go1.5.3
Git commit: 590d5108
Built: Thu Feb 4 18:36:33 2016
OS/Arch: linux/amd64Server:
Version: 1.10.0
API version: 1.22
Go version: go1.5.3
Git commit: 590d5108
Built: Thu Feb 4 18:36:33 2016
OS/Arch: linux/amd64
##Working With Docker
###Downloading a Docker Container
Let’s start using docker. You will need to have an image present on your host machine where the containers will exist. You can download the CentOS docker image by running the following command.
sudo docker pull centos
You can see the output some thing like this:
Using default tag: latest
latest: Pulling from library/centosa3ed95caeb02: Pull complete
196355c4b639: Pull complete
Digest: sha256:381f21e4c7b3724c6f420b2bcfa6e13e47ed155192869a2a04fa10f944c78476
Status: Downloaded newer image for centos:latest
###Running a Docker Container
Now, You just run one command to setup a basic CentOS container with a bash shell.
To run a command in new container, Run:
sudo docker run -i -t centos /bin/bash
Note: -i flag attaches stdin and stdout and -t flag allocates a tty.
That’s it. Now you’re using a bash shell inside of a centos docker container.
There are many containers already available on docker website. You can found any container through a search. For example to search centos container, Run:
sudo docker search centos
You can see the output some thing like this:
NAME DESCRIPTION STARS OFFICIAL AUTOMATED
centos The official build of CentOS. 2079 [OK]
jdeathe/centos-ssh CentOS-6 6.7 x86_64 / CentOS-7 7.2.1511 x8... 19 [OK]
jdeathe/centos-ssh-apache-php CentOS-6 6.7 x86_64 / Apache / PHP / PHP M... 14 [OK]
million12/centos-supervisor Base CentOS-7 with supervisord launcher, h... 10 [OK]
blalor/centos Bare-bones base CentOS 6.5 image 8 [OK]
nimmis/java-centos This is docker images of CentOS 7 with dif... 8 [OK]
torusware/speedus-centos Always updated official CentOS docker imag... 7 [OK]
centos/mariadb55-centos7 3 [OK]
nickistre/centos-lamp LAMP on centos setup 3 [OK]
nathonfowlie/centos-jre Latest CentOS image with the JRE pre-insta... 3 [OK]
consol/sakuli-centos-xfce Sakuli end-2-end testing and monitoring co... 2 [OK]
timhughes/centos Centos with systemd installed and running 1 [OK]
darksheer/centos Base Centos Image -- Updated hourly 1 [OK]
softvisio/centos Centos 1 [OK]
lighthopper/orientdb-centos A Dockerfile for creating an OrientDB imag... 1 [OK]
yajo/centos-epel CentOS with EPEL and fully updated 1 [OK]
grayzone/centos auto build for centos. 0 [OK]
ustclug/centos USTC centos 0 [OK]
januswel/centos yum update-ed CentOS image 0 [OK]
dmglab/centos CentOS with some extras - This is for the ... 0 [OK]
jsmigel/centos-epel Docker base image of CentOS w/ EPEL installed 0 [OK]
grossws/centos CentOS 6 and 7 base images with gosu and l... 0 [OK]
labengine/centos Centos image base 0 [OK]
lighthopper/openjdk-centos A Dockerfile for creating an OpenJDK image... 0 [OK]
blacklabelops/centos CentOS Base Image! Built and Updates Daily! 0 [OK]
You can also list all available images on your system using the following command:
sudo docker images
You can see the output some thing like this:
REPOSITORY TAG IMAGE ID CREATED SIZE
firefox-instance latest 8e61bff07fa0 3 weeks ago 354.6 MB
centos latest d0e7f81ca65c 4 weeks ago 196.6 MB
debian latest f50f9524513f 4 weeks ago 125.1 MB
apache/ubuntu latest 196655130bc9 4 weeks ago 224.1 MB
apache-instance latest 7da78270c5f7 4 weeks ago 224.1 MB
apache-instance ubuntu 7da78270c5f7 4 weeks ago 224.1 MB
hitjethva/apache-instance ubuntu 7da78270c5f7 4 weeks ago 224.1 MB
##Docker basic command lines
Let’s start with seeing all available commands docker have.
You can list all available docker command by running the following command:
sudo docker
You should see the following output:
Commands:
``` language-bash
attach Attach 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
diff Inspect changes on a container's filesystem
events Get real time events from the server
exec Run a command in a running container
export Export a container's filesystem as a tar archive
history Show the history of an image
images List images
import Import the contents from a tarball to create a filesystem image
info Display system-wide information
inspect Return low-level information on a container or image
kill Kill a running container
load Load an image from a tar archive or STDIN
login Register or log in to a Docker registry
logout Log out from a Docker registry
logs Fetch the logs of a container
network Manage Docker networks
pause Pause all processes within a container
port List port mappings or a specific mapping for the CONTAINER
ps List containers
pull Pull an image or a repository from a registry
push Push an image or a repository to a registry
rename Rename a container
restart Restart a container
rm Remove one or more containers
rmi Remove one or more images
run Run a command in a new container
save Save an image(s) to a tar archive
search Search the Docker Hub for images
start Start one or more stopped containers
stats Display a live stream of container(s) resource usage statistics
stop Stop a running container
tag Tag an image into a repository
top Display the running processes of a container
unpause Unpause all processes within a container
update Update resources of one or more containers
version Show the Docker version information
volume Manage Docker volumes
wait Block until a container stops, then print its exit code
Run ‘docker COMMAND –help’ for more information on a command.
To check system-wide information on docker, run:`sudo docker info`
You should see the following output:
Containers: 6 Running: 0 Paused: 0 Stopped: 6 Images: 22 Server Version: 1.10.0 Storage Driver: aufs Root Dir: /var/lib/docker/aufs Backing Filesystem: extfs Dirs: 35 Dirperm1 Supported: false Execution Driver: native-0.2 Logging Driver: json-file Plugins: Volume: local Network: bridge null host Kernel Version: 3.13.0-32-generic Operating System: Zorin OS 9 OSType: linux Architecture: x86_64 CPUs: 4 Total Memory: 3.746 GiB Name: Vyom-PC ID: G2NZ:3DDJ:KJFV:HC2E:HR3Y:J4JH:TX2D:EX57:K26Y:3AFH:FGKB:XEIF Username: hitjethva Registry: https://index.docker.io/v1/ WARNING: No swap limit support
You can use the following command to list all running containers:`sudo docker ps`
You can see the running container in following image:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 534544f2e924 centos “/bin/bash” 30 seconds ago Up 29 seconds boring_hamilton “`
You can also list both running and non-running containers by running the following command:
sudo docker ps -a
Sometimes container stops due to its process ending or you stopping it explicitly. In this situation you can run container again with container ID.
sudo docker run "container ID"
You can also stop a running container by running the following command:
sudo docker stop "container ID"
Note: You can find container ID using sudo docker ps command.
If you would like to save the changes you have made with a container, use commit command to save to save it as an image.
sudo docker commit "container ID" image_name
This command turns your container to an image. You can roll back when your container you need.
If you want to attach into a running container, Docker allows you to interaction with running containers using the attach command.
You can use attach command with the container ID..
sudo docker attach "container ID"
##Stop and Delete all Containers and Images
To stop all running containers, Run:
sudo docker stop $(docker ps -a -q)
To delete all existing containers, Run:
sudo docker rm $(docker ps -a -q)
To delete all existing images, Run:
sudo docker rmi $(docker images -q -a)
##Conclusion
Congratulations! You now have a centos server with a Docker platform for your application development environment.
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