Docker is a software for automating the deployment and management of applications in an operating system-level virtualization environment. It allows you to package an application with all its environment and dependencies into a container that can be ported to any Linux system with kernel cgroups support and provides a container management environment

    file

    You can learn how to install Docker in this manual

    Using the Docker command

    The docker command allows you to use various options, commands with arguments. The syntax is as follows:
    ``.shell
    docker [option] [command] [arguments]

    To see all available subcommands, type:  
    ``.shell
    docker  
    

    The complete list will look like this:
    ``.shell
    attach Attach local standard input, output, and error streams to a running container
    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
    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 Pull an image or a repository from a registry
    push Push Push an image or a repository to a registry
    rename Rename Rename a container
    restart Restart one or more containers
    rm Remove one or more containers
    rmi Remove one or more images
    run Run Run a command in a new container
    save Save Save one or more images to a tar archive (streamed to STDOUT by default)
    search Search the Docker Hub for images
    start Start Start one or more stopped containers
    stats Display a live stream of container(s) resource usage statistics
    stop 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 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 see the options to use a certain command, type  
    ``.shell
    docker docker-subcommand --help  
    

    To view all the information about Docker, you can use the command:
    ``.shell
    docker info

    **Working with Docker images**
    
    By default, Docker gets images from the [Docker Hub](https://hub.docker.com/), which is a registry of images maintained by Docker  
    
    To check if you can access and download images from Docker Hub, type the following command:  
    ``.shell
    docker run hello-world  
    

    The correct result of this command, which means that Docker is working correctly, is shown below:
    ``.shell
    [email protected]:~# docker run hello-world
    Unable to find image 'hello-world:latest' locally
    latest: Pulling from library/hello-world
    0e03bdcc26d7: Pull complete
    Digest: sha256:8e3114318a995a1ee497790535e7b88365222a21771ae7e53687ad76563e8e76
    Status: Downloaded newer image for hello-world:latest

    Hello from Docker!
    This message shows that your installation appears to be working correctly.

    
    Initially, Docker couldn't find the hello-world image locally, so it downloaded the image from the Docker Hub, which is the default repository. After downloading the image, Docker created a container from the image and ran the application in the container, displaying a message.  
    
    The images available in Docker Hub can be searched using the docker command and the search subcommand.  
    ``.shell
    docker search ubuntu  
    

    The script looks through the Docker Hub and returns a list of all images whose names match the given search
    ``.shell
    [email protected]:~# docker search ubuntu
    NAME DESCRIPTION STARS OFFICIAL AUTOMATED
    ubuntu Ubuntu is a Debian-based Linux operating sys... 10856 [OK]
    dorowu/ubuntu-desktop-lxde-vnc Docker image to provide HTML5 VNC interface ... 420 [OK]
    rastasheep/ubuntu-sshd Dockerized SSH service, built on top of offi... 244 [OK]
    consol/ubuntu-xfce-vnc Ubuntu container with "headless" VNC session... 216 [OK]
    ubuntu-upstart Upstart is an event-based replacement for th... 107 [OK]
    ansible/ubuntu14.04-ansible Ubuntu 14.04 LTS with ansible 98 [OK]
    1and1internet/ubuntu-16-nginx-php-phpmyadmin-mysql-5 ubuntu-16-nginx-php-phpmyadmin-mysql-5 50 [OK]
    ubuntu-debootstrap debootstrap --variant=minbase --components=m... 44 [OK]
    nuagebec/ubuntu Simple always updated Ubuntu docker images w... 24 [OK]
    i386/ubuntu Ubuntu is a Debian-based Linux operating sys... 19
    1and1internet/ubuntu-16-apache-php-5.6 ubuntu-16-apache-php-5.6 14 [OK]
    1and1internet/ubuntu-16-apache-php-7.0 ubuntu-16-apache-php-7.0 13 [OK]
    eclipse/ubuntu_jdk8 Ubuntu, JDK8, Maven 3, git, curl, nmap, mc, ... 12 [OK]
    1and1internet/ubuntu-16-nginx-php-phpmyadmin-mariadb-10 ubuntu-16-nginx-php-phpmyadmin-mariadb-10 11 [OK]
    1and1internet/ubuntu-16-nginx-php-5.6 ubuntu-16-nginx-php-5.6 8 [OK]
    1and1internet/ubuntu-16-nginx-php-5.6-wordpress-4 ubuntu-16-nginx-php-5.6-wordpress-4 7 [OK]
    1and1internet/ubuntu-16-apache-php-7.1 ubuntu-16-apache-php-7.1 6 [OK]
    darksheer/ubuntu Base Ubuntu Image -- Updated hourly 5 [OK]
    pivotaldata/ubuntu A quick freshening-up of the base Ubuntu doc... 4
    1and1internet/ubuntu-16-nginx-php-7.0 ubuntu-16-nginx-php-7.0 4 [OK]
    ubuntu16.04-build Ubuntu 16.04 image for GPDB compilation 2
    smartentry/ubuntu ubuntu with smartentry 1 [OK]
    1and1internet/ubuntu-16-sshd ubuntu-16-sshd 1 [OK]
    1and1internet/ubuntu-16-php-7.1 ubuntu-16-php-7.1 1 1 [OK]
    pivotaldata/ubuntu-gpdb-dev Ubuntu images for GPDB development 1

    
    In the **OFFICIAL** column, the line **OK** shows that the image is built and supported by the company that is developing this project. When the desired image is selected, you can download it to your computer using the **pull** subcommand.  
    
    For example, downloading the official ubuntu image to your computer:  
    ``.shell
    docker pull ubuntu  
    

    You will see a similar result:
    ``.shell
    [email protected]:~# docker pull ubuntu
    Using default tag: latest
    latest: Pulling from library/ubuntu
    d51af753c3d3: Pull complete
    fc878cd0a91c: Pull complete
    6154df8ff988: Pull complete
    fee5db0ff82f: Pull complete
    Digest: sha256:747d2dbbaaee995098c9792d99bd333c6783ce56150d1b11e333bbceed5c54d7
    Status: Downloaded newer image for ubuntu:latest
    docker.io/library/ubuntu:latest

    After downloading the image, you can start the container with the downloaded image using the **run** subcommand  
    
    To view the downloaded images, type:  
    ``.shell
    docker images  
    

    You will see a result like this:
    ``.shell
    [email protected]:~# docker images
    REPOSITORY TAG IMAGE ID CREATED SIZE
    ubuntu latest 1d622ef86b13 10 days ago 73.9MB
    hello-world latest bf756fb1ae65 4 months ago 13.3kB

    
    **Starting the Docker container**
    
    The hello-world container is an example of a container that starts and finishes after a test message is output. Containers are similar to virtual machines, but are less demanding on resources.  
    
    The combination of the parameters **-i** and **-t** gives interactive access to the container's command processor:  
    ``.shell
    docker run -it ubuntu  
    

    The command line will show that we are working in the container:
    ``.shell
    [email protected]:/#

    Next, we can run commands inside the container  
    ``.shell
    apt update  
    

    Install Node.js:
    ``.shell
    apt install nodejs

    This command installs Node.js in a container from the official Ubuntu repository  
    
    Check that Node.js is installed:  
    ``.shell
    node -v  
    

    ``.shell
    [email protected]:/# node -v
    v10.19.0

    Changes that are executed inside a container only apply to that container.  
    
    To exit the container, type **exit**.  
    
    **Manage Docker Containers**
    
    Once you start using Docker, you'll have many active and inactive containers on your machine  
    To view active containers, type the command:  
    ``.shell
    docker ps  
    

    ``.shell
    [email protected]:~# docker ps
    CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES

    To see the active and inactive containers, run docker ps with parameter **-a**:  
    ``.shell
    docker ps -a  
    

    ``.shell
    [email protected]:~# docker ps -a
    CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
    bb5be2ace9f4 ubuntu "/bin/bash" 22 minutes ago Exited (0) 4 minutes ago
    6d0063c3eb57 hello-world "/hello" 40 minutes ago Exited (0) 40 minutes ago flamboyant_hellman
    9c961614171d hello-world "/hello" 3 hours ago Exited (0) 3 hours ago gifted_bose

    To see the last of the created containers, specify parameter **-l**:  
    ``.shell
    docker ps -l  
    

    ``.shell
    [email protected]:~# docker ps -l
    CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
    bb5be2ace9f4 ubuntu "/bin/bash" 25 minutes ago Exited (0) 6 minutes ago

    To start a stopped container, use the command **docker start** and specify the container ID or name  
    ``.shell
    docker start bb5be2ace9f4  
    

    You can now use docker ps to see its status:
    ``.shell
    [email protected]:~# docker ps
    CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
    bb5be2ace9f4 ubuntu "/bin/bash" 29 minutes ago Up 25 seconds

    To stop a running container, use the command **docker stop** and specify the container ID or name  
    ``.shell
    docker stop adoring_williams  
    

    If you don't need the container anymore, delete it with the command docker rm specifying the container ID or name. To find the container ID or name, use the command docker ps -a. The container can then be deleted.
    ``.shell
    docker rm adoring_williams

    
    **Saving changes in the container to a Docker image**
    
    When you run the container from a Docker image, you can create, modify and delete files, just as you would on a virtual machine.  
    
    After installing Node.js in an Ubuntu container, you will have a container running from the image, but it will be different from the image used to create it. However, you may need such a Node.js container as the basis for future images.  
    
    Then confirm the changes in the new Docker image with the following command  
    ``.shell
    docker commit -m "What you did to the image" -a "Author Name" container_id repository/new_image_name  
    

    Parameter -m allows you to specify a confirmation message, parameter -a allows you to specify an author. The container_id identifier is the identifier that was used before. If you have not created additional repositories in Docker Hub, the repository name is usually your user name in Docker Hub.

    For example, for user test and container ID bb5be2ace9f4, the command would look like this:
    ``.shell
    docker commit -m "added Node.js" -a "test" bb5be2ace9f4 test/ubuntu-nodejs

    After the image has been committed, the new image is saved locally on your computer  
    
    If you browse the list of Docker images, you will find both the new image and the original image on which it was based:  
    ``.shell
    docker images  
    

    You will see a similar result:
    ``.shell
    [email protected]:~# docker images
    REPOSITORY TAG IMAGE ID CREATED SIZE
    test/ubuntu-nodejs latest 008c1c057944 51 seconds ago 162MB
    ubuntu latest 1d622ef86b13 10 days ago 73.9MB
    hello-world latest bf756fb1ae65 4 months ago 13.3kB
    ```
    In this example, ubuntu-nodejs is a new image created from an existing ubuntu image from the Docker Hub.