I am going to show you how to install docker in Linux platform, the operating system I am using here is CentOS 7 64 bit architecture. In my previous tutorial I had shown how to install docker on Windows 7 operating system.
Docker is a container, more like a virtual machine, portable, resource friendly and dependent on the host operating system. Using docker makes an application simple and easy to run in a container.
Why do you need docker?
It allows developers to create a portable application that could be run on every machine. Instead of delivering jar, war, ear or other type of artifacts for your applications, you deliver an image and someone else who wants to deploy your application, basically deploys the image on a machine with pre-installed docker. With docker installed you don’t have dependency of setting up the environments.
CentOS 7 64 bit droplet, Non-root user with sudo privilege
before you install docker on your system, make sure you get the latest docker package from the official docker repository, because the available docker package in your CentOS droplet may not be the latest version. To get the latest version execute the following commands. The first command will update your package database and the second command will download the latest version from docker official repository and install it.
$ sudo yum check-update $ curl -fsSL https://get.docker.com/ | sh
-fsSL has the following meaning:
- f: Fail silently (no output at all) on server errors.
- s: Silent or quiet mode. Don’t show progress meter or error messages.
- S: When used with
-sit makes curl show an error message if it fails.
- L: (HTTP/HTTPS) If the server reports that the requested page has moved to a different location (indicated with a Location: header and a 3XX response code), this option will make curl redo the request on the new place.
| sh with
curl command starts
sh at the same time, connecting the output of
curl to the input of
curl will carry out with the download as fast as
sh can run the script.
Once the installation has been completed, you will see similar screen as shown in the following image:
Installation complete, now you can start the docker using the following command:
$ sudo systemctl start docker
Now you can check the status of the docker whether it is running or not:
$ sudo systemctl status docker
The output should be similar to the below image:
Finally, make sure it starts on every server reboot by following command:
$ sudo systemctl enable docker
You can view all available sub-commands using the command
$ docker. It will list the following commands:
attach Attach local standard input, output, and error streams 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 deploy Deploy a new stack or update an existing stack diff Inspect changes to files or directories 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 Docker objects kill Kill one or more running containers load Load an image from a tar archive or STDIN login Log in to a Docker registry logout Log out from a Docker registry logs Fetch the logs of a container pause Pause all processes within one or more containers 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 one or more containers rm Remove one or more containers rmi Remove one or more images run Run a command in a new container save Save one or more images to a tar archive (streamed to STDOUT by default) 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 one or more running containers tag Create a tag TARGET_IMAGE that refers to SOURCE_IMAGE top Display the running processes of a container unpause Unpause all processes within one or more containers update Update configuration of one or more containers version Show the Docker version information wait Block until one or more containers stop, then print their exit codes Run 'docker COMMAND --help' for more information on a command.
You may also view system wide information using the command
$ docker info.
At this point you might get permission denied or access denied error if you have not added the user into docker group after the installation.
Perform the following steps in order to add the user.
- Execute command
$ sudo usermod -aG docker <user name>
- Reflect the change using command
$ newgrp docker
- Restart docker
$ sudo systemctl restart docker
Now you can re-execute the command
$ docker info to view system wide information.
Docker containers run from docker images and these images are pulled from docker hub, a registry managed by docker. Anyone can build and host docker images into docker hub. Most of the applications that you need to run docker containers have docker images in docker hub.
You can check whether docker hub is accessible or not by using the following command:
$ docker run hello-world
The following output shows docker is working properly:
To list docker images on your system you can use the following command:
$ docker images
In the following image you can see that the only image I had puleed from docker hub in the previous step:
You can also check which docker containers are currently running by executing the command
$ docker ps.
That’s all about installing docker in CentsOS 7 operating system.