Archive for the ‘Docker’ Category

Installing Docker on Ubuntu 18.04

Posted: 10 August 2018 in Docker

In this post i will put down the steps to install docker on Ubuntu 18.04.


  • Installed os version is Ubuntu 18.04
  • Configured firewall
  • non-root sudo user available

Step 1 — Installing Docker

The Docker installation package available in the official Ubuntu repository may not be the latest version. To ensure we get the latest version, we’ll install Docker from the official Docker repository. To do that, we’ll add a new package source, add the GPG key from Docker to ensure the downloads are valid, and then install the package.

First, update your existing list of packages:

$ sudo apt update

Next, install a few prerequisite packages which let apt use packages over HTTPS:

$ sudo apt install apt-transport-https ca-certificates curl software-properties-common

Then add the GPG key for the official Docker repository to your system:

$ curl -fsSL | sudo apt-key add -

Add the Docker repository to APT sources:

$ sudo add-apt-repository "deb [arch=amd64] bionic stable"

Next, update the package database with the Docker packages from the newly added repo:

$ sudo apt update

Finally, install Docker:

$ sudo apt install docker-ce

Docker should now be installed, the daemon started, and the process enabled to start on boot. Check that it’s running:

$ sudo systemctl status docker

The output should be similar to the following, showing that the service is active and running:

● docker.service - Docker Application Container Engine
   Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
   Active: active (running) since Thu 2018-07-05 15:08:39 UTC; 2min 55s ago
 Main PID: 10096 (dockerd)
    Tasks: 16
   CGroup: /system.slice/docker.service
           ├─10096 /usr/bin/dockerd -H fd://
           └─10113 docker-containerd --config /var/run/docker/containerd/containerd.toml

Installing Docker now gives you not just the Docker service (daemon) but also the docker command line utility, or the Docker client. We’ll explore how to use the docker command later in this tutorial.

Step 2 — Executing the Docker Command Without Sudo (Optional)

By default, the docker command can only be run the root user or by a user in the docker group, which is automatically created during Docker’s installation process. If you attempt to run the docker command without prefixing it with sudo or without being in the docker group, you’ll get an output like this:

docker: Cannot connect to the Docker daemon. Is the docker daemon running on this host?.
See 'docker run --help'.

If you want to avoid typing sudo whenever you run the docker command, add your username to the docker group:

$ sudo usermod -aG docker ${USER}


To apply the new group membership, log out of the server and back in, or type the following:

$ su - ${USER}


You will be prompted to enter your user’s password to continue.

Confirm that your user is now added to the docker group by typing:

$ id -nG


The output should now state that you are in the docker group. If you need to add a user to the docker group that you’re not logged in as, declare that username explicitly using:

$ sudo usermod -aG docker username


The rest of this article assumes you are running the docker command as a user in the docker group. If you choose not to, please add sudo in front of the commands.

Let’s explore the docker command next.

Step 3 — Using the Docker Command

Using docker consists of passing it a chain of options and commands followed by arguments. The syntax takes this form:

$ docker [option] [command] [arguments]


To view all available subcommands, type:

$ docker


As of Docker 18, the complete list of available subcommands includes:


  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
  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


To view the options available to a specific command, type:

$ docker docker-subcommand --help


To view system-wide information about Docker, use:

$ docker info


I will explore some of these commands in another blog post. We’ll start by working with images.


To connect to a running docker container and change files residing within the container you need to start an interactive session. First list all the running containers with the following command:

docker ps
CONTAINER ID        IMAGE                       COMMAND                  CREATED             STATUS         
08a9a1701107        rabbitmq:3.7.3-management   "docker-entrypoint.s…"   3 hours ago         Up About an hour

Docker will list all your running container as seen above. The column CONTAINER ID is important and we will be using this ID to connect to the interactive session of that container. To connect to the container enter the following command:

docker exec -it 08a9a1701107 su -

alternative for the CONTAINER ID is the container name if you happen to know this. In my case this would be:

docker exec -it rabbitmq-docker su -

What is docker!?

Posted: 8 August 2018 in Docker

Docker is a computer program that performs operating-system-level virtualization also known as containerization.[6] It was first released in 2013 and is developed by Docker, Inc.[7]

Docker is used to run software packages called “containers”. In a typical example use case, one container runs a web server and web application, while a second container runs a database server that is used by the web application. Containers are isolated from each other and bundle their own tools, libraries and configuration files; they can communicate with each other through well-defined channels. All containers are run by a single operating system kernel and are thus more lightweight than virtual machines. Containers are created from “images” that specify their precise contents. Images are often created by combining and modifying standard images downloaded from repositories.