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1. Install

  • i. Log into your Ubuntu installation as a user with sudo privileges.
  • ii. Verify that you have wget installed.

    • Check
      $ which wget
    • If wget isn't installed, install it after updating your manager:
      $ sudo apt-get update
      $ sdo apt-get install wget
  • iii. Get the latest Docker package.

    • The system prompts you for your sudo password. Then, it downloads and installs Docker and its dependencies.
      $ wget -q0- | sh
    • Note1: If your company is behind a filtering proxy, you may find that the apt-key command fails for the Docker repo during installation. To work around this, add the key directly using the following:
      $ wget -qO- | sudo apt-key add -
    • Note2: Docker currently only supports 64bit platforms.
  • iv: Verify docker is installed correctly:

    $ docker run hello-world
      Unable to find image 'hello-world:latest' locally
    latest: Pulling from library/hello-world
    535020c3e8ad: Pull complete
    af340544ed62: Pull complete
    Digest: sha256:a68868bfe696c00866942e8f5ca39e3e31b79c1e50feaee4ce5e28df2f051d5c
    Status: Downloaded newer image for hello-world:latest
    • The following message shows that your installation appears to be working correctly.
      Hello from Docker.
    • To generate this message, Docker took the following steps:

        1. The Docker client contacted the Docker daemon.
        1. The Docker daemon pulled the "hello-world" image from the Docker Hub.
        1. The Docker daemon created a new container from that image which runs the executable that produces the output you are currently reading.
        1. The Docker daemon streamed that output to the Docker client, which sent it to your terminal.
    • To try something more ambitious, you can run an Ubuntu container with:

      $ docker run -it ubuntu bash
    • Share images, automate workflows, and more with a free Docker Hub account:
    • For more examples and ideas, visit:

2. About images & containers

  • As the last step in your installation, you ran the docker run hello-world command. With this one command, you completed the core tasks to using Docker. The command you ran had three parts.


  • A container: A container is a stripped-to-basics version of a Linux operating system.
  • An image: An image is software you load into a container.
  • When you ran the command, the Docker software:
    1. checked to see if you had the hello-word software image
    2. downloaded the image from the Docker Hub (more about the hub later)
    3. loaded the image into the container and “ran” it
  • Depending on how it was built, an image might run a simple, single command and then exit. This is what hello-world did.
  • A Docker image, though, is capable of much more. An image can start software as complex as a database, wait for you (or someone else) to add data, store the data for later use, and then wait for the next person.
  • Who built the hello-world software image though? In this case, Docker did but anyone can. Docker lets people (or companies) create and share software through Docker images. Using Docker, you don't have to worry about whether your computer can run the software in a Docker image — a Docker container can always run it.

3. About finding the whalesay image

  • People all over the world create Docker images. You can find these images by browsing the Docker Hub.
Step1: Locate the whalesay image
  • i. Open your browser and browse to the Docker Hub.
    • The Docker Hub contains images from individuals like you and official images from organizations like RedHat, IBM, Google, and a whole lot more.
  • ii. Click Browser & Search.
  • iii. Enter the word whalesay in the search bar.
  • iv. Click on the docker/whalesay image in the results.
    • Each image repository contains information about an image. It should include information such as what kind of software the image contains and how to use it. You may notice that the whalesay image is based on a Linux distribution called Ubuntu. In the next step, you run the whalesay image on your machine.
Step2: Run the Whalesay image
  • i. Call the following comand in the terminal:
    • The first time you run a software image, the docker command looks for it on your local system. If the image isn't there, then docker gets it from the hub.
      $ docker run docker/whalesay cowsay boo
  • ii. Find what images you have by calling the following command:
    • When you run an image in a container, Docker downloads the image to your computer. This local copy of the image saves you time. Docker only downloads the image again if the image's source changes on the hub. You can, of course, delete the image yourself. (You'll learn more about that later)
      $ docker images
      REPOSITORY           TAG         IMAGE ID            CREATED            VIRTUAL SIZE
      docker/whalesay      latest      fb434121fc77        3 hours ago        247 MB
      hello-world          latest      91c95931e552        5 weeks ago        910 B

4. About building an image

Step1: Write a Dockerfile
  • i. Make a new directory:

    $ mkdir mydocker build
  • ii. Create a text file called Dockerfile in te new directory:

    • A Dockerfile describes the software that is “baked” into an image. It isn't just ingredients tho, it can tell the software what environment to use or what commands to run. Your recipe is going to be very short.
      $ cd mkdocker
      $ vim Dockerfile
  • iii. Add a line to the text file:
    • The FROM keyword tells Docker which image your image is based on. Whalesay is cute and has the cowsay program already, so we'll start there.
      FROM docker/whalesay:latest
  • iv. Add the fortunes programe to the image:
    • The fortunes program has a command that prints out wise sayings for our whale to say. So, the first step is to install it. This line installs the software into the image.
      RUN apt-get -y update && apt-get install -y fortunes
  • v. Once the image has the software it needs, you instruct the software to run when the image is loaded:
    • This line tells the fortune program to pass a nifty quote to the cowsay program.
      CMD /usr/games/fortune -a | cowsay
  • vi. Save and close the text file.
  • At this point, you have all your software ingredients and behaviors described in a Dockerfile. You are ready to build a new image
Step2: Build an image from your Dockerfile
  • Now, build your new image by typing the docker build -t docker-whale . command in your terminal (don't forget the . period). (This proccess will take several seconds to run and reports its outcomd)

    Sending build context to Docker daemon 158.8 MB
    Removing intermediate container a8e6faa88df3
    Successfully built 7d9495d03763
Step3: Learn about the build process
  • The docker build -t docker-whale . command takes the Dockerfile in the current directory, and builds an image called docker-whale on your local machine. The command takes about a minute and its output looks really long and complex. In this section, you learn what each message means.
  • First Docker checks to make sure it has everything it needs to build.

    Sending build context to Docker daemon 158.8 MB
  • Then, Docker loads with the whalesay image. It already has this image locally as your might recall from the last page. So, Docker doesn't need to download it.

    Step 0 : FROM docker/whalesay:latest
    ---> fb434121fc77
  • Docker moves onto the next step which is to update the apt-get package manager. This takes a lot of lines, no need to list them all again here.

    Step 1 : RUN apt-get -y update && apt-get install -y fortunes
    ---> Running in 27d224dfa5b2
    Ign trusty InRelease
    Ign trusty-updates InRelease
    Ign trusty-security InRelease
    Hit trusty Release.gpg
    Get:15 trusty-security/restricted amd64 Packages [14.8 kB]
    Get:16 trusty-security/universe amd64 Packages [134 kB]
    Reading package lists...
    ---> eb06e47a01d2
  • Then, Docker installs the new fortunes software.

    Removing intermediate container e2a84b5f390f
    Step 2 : RUN apt-get install -y fortunes
    ---> Running in 23aa52c1897c
    Reading package lists...
    Building dependency tree...
    Reading state information...
    The following extra packages will be installed:
    fortune-mod fortunes-min librecode0
    Suggested packages:
    x11-utils bsdmainutils
    The following NEW packages will be installed:
    fortune-mod fortunes fortunes-min librecode0
    0 upgraded, 4 newly installed, 0 to remove and 3 not upgraded.
    Need to get 1961 kB of archives.
    After this operation, 4817 kB of additional disk space will be used.
    Get:1 trusty/main librecode0 amd64 3.6-21 [771 kB]
    Setting up fortunes (1:1.99.1-7) ...
    Processing triggers for libc-bin (2.19-0ubuntu6.6) ...
    ---> c81071adeeb5
    Removing intermediate container 23aa52c1897c
  • Finally, Docker finishes the build and reports its outcome

    Step 3 : CMD /usr/games/fortune -a | cowsay
    ---> Running in a8e6faa88df3
    ---> 7d9495d03763
    Removing intermediate container a8e6faa88df3
    Successfully built 7d9495d03763
Step 4: Run your new docker-whale
  • i. Check the new image you created:

    $ docker images
    REPOSITORY           TAG          IMAGE ID          CREATED             VIRTUAL SIZE
    docker-whale         latest       7d9495d03763      4 minutes ago       273.7 MB
    docker/whalesay      latest       fb434121fc77      4 hours ago         247 MB
    hello-world          latest       91c95931e552      5 weeks ago         910 B
  • ii. Run your new image by typing docker run docker-whale:

    $ docker run docker-whale

5. About creating a repository

Step 1: Sign up an acount on Docker Hub
Step 2: Verify your email and add a repository

6. Tag, push and pull images

Step 1: Tag and push the image
  • i. List the images you currently have:

    $ docker images
    REPOSITORY           TAG          IMAGE ID            CREATED             VIRTUAL SIZE
    docker-whale         latest       7d9495d03763        38 minutes ago      273.7 MB
    <none>               <none>       5dac217f722c        45 minutes ago      273.7 MB
    docker/whalesay      latest       fb434121fc77        4 hours ago         247 MB
    hello-world          latest       91c95931e552        5 weeks ago         910 B
  • ii. Find the IMAGE ID for your docker-whale image.

    • In this case, the id is 7d9495d03763.
    • You'll notice that currently, the REPOSITORY shows the repository but not the namespace for docker-whale. You need to include the namespace for Docker Hub to associate it with your account. The namespace is the same as your account name.
  • iii. Use IMAGE ID and the docker tag command to tag your docker-whale image.

  • iii. Type the docker images command again to see your newly tagged image.

    $ docker images
    REPOSITORY                  TAG       IMAGE ID        CREATED          VIRTUAL SIZE
    maryatdocker/docker-whale   latest    7d9495d03763    5 minutes ago    273.7 MB
    docker-whale                latest    7d9495d03763    2 hours ago      273.7 MB
    <none>                      <none>    5dac217f722c    5 hours ago      273.7 MB
    docker/whalesay             latest    fb434121fc77    5 hours ago      247 MB
    hello-world                 latest    91c95931e552    5 weeks ago      910 B
  • iv. Use the docker login command to log into the Docker Hub from the command line.

    docker login --username=yourhubusername --password=yourpassword
  • v. Type the docker push command to push your image to your new repository.

    $ docker push maryatdocker/docker-whale
    The push refers to a repository [maryatdocker/docker-whale] (len: 1)
    7d9495d03763: Image already exists
    c81071adeeb5: Image successfully pushed
    eb06e47a01d2: Image successfully pushed
    fb434121fc77: Image successfully pushed
    5d5bd9951e26: Image successfully pushed
    99da72cfe067: Image successfully pushed
    1722f41ddcb5: Image successfully pushed
    5b74edbcaa5b: Image successfully pushed
    676c4a1897e6: Image successfully pushed
    07f8e8c5e660: Image successfully pushed
    37bea4ee0c81: Image successfully pushed
    a82efea989f9: Image successfully pushed
    e9e06b06e14c: Image successfully pushed
    Digest: sha256:ad89e88beb7dc73bf55d456e2c600e0a39dd6c9500d7cd8d1025626c4b985011
Step 2: Pull a new image
  • In this last section, you'll pull the image you just pushed to hub. Before you do that though, you'll need to remove the original image from your local machine. If you left the original image on your machine. Docker would not pull from the hub — why would it? The two images are identical.
  • i. Use the docker rmi to remove the maryatdocker/docker-whale and docker-whale images.

    • You can use an ID or the name to remove an image.
      $ docker rmi -f 7d9495d03763
      $ docker rmi -f docker-whale
  • ii. Pull a new image from your repository using the docker pull command.

    • The command you type should include your username from Docker Hub.
      $ docker pull yourusername/docker-whale
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