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 looks like this:
    ``.shell
    docker [option] [command] [arguments]

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

    The complete list will look like this:
    ``.shell
    Commands:
    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

    ~~~.shell
    [email protected]:~# docker info  
    Client:  
     Debug Mode: false
    
    Server:  
     Containers: 0
      Running: 0
      Paused: 0
      Stopped: 0
     Images: 0
     Server Version: 19.03.8
     Storage Driver: overlay2
      Backing Filesystem <unknown>
      Supports d_type: true
      Native Overlay Diff: true
     Logging Driver: json-file
     Cgroup Driver: cgroupfs
     Plugins:
      Volume: local
      Network: bridge host ipvlan macvlan null overlay
      Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
     Swarm: inactive
     Runtimes: runc
     Default Runtime: runc
     Init Binary: docker-init
     containerd version: 7ad184331fa3e55e52b890ea95e65ba581ae3429
     runc version: dc9208a3303feef5b3839f4323d9beb36df0a9dd
     init version: fec3683
     Security Options:
      seccomp
       Profile: default
     Kernel Version: 4.9.0-11-amd64
     Operating System: Debian GNU/Linux 9 (stretch)
     OSType: linux
     Architecture: x86_64
     CPUs: 1
     Total Memory: 996.5MiB
     Name: kvmde67-19464.fornex.org
     ID: HSOZ:FUYF:W3OM:FR4R:LDBZ:LPC2:GPF2:VD54:RRSU:PC34:XFRM:URDD
     Docker Root Dir: /var/lib/docker
     Debug Mode: false
     Registry: https://index.docker.io/v1/
     Labels:
     Experimental: false
     Insecure Registries:
      127.0.0.0/8
     Live Restore Enabled: false
    ~~~
    
    **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 debian  
    

    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 debian
    NAME DESCRIPTION STARS OFFICIAL AUTOMATED
    ubuntu Ubuntu is a Debian-based Linux operating sys... 10866 [OK]
    debian Debian is a Linux distribution that's compos... 3473 [OK]
    arm32v7/debian Debian is a Linux distribution that's compos... 64
    itcaro/debian-ssh debian:jessie 28 [OK]
    samueldebruyn/debian-git a minimal docker container with debian and g... 22 [OK]
    arm64v8/debian Debian is a Linux distribution that's compos... 22
    multiarch/debian-debootstrap multiarch ports of debian-debootstrap 11
    i386/debian Debian is a Linux distribution that's compos... 10
    eboraas/debian Debian base images, for all currently-availa... 8 [OK]
    vergissberlin/debian-development Docker debian image to use for development, ... 6 [OK]
    smartentry/debian debian with smartentry 4 [OK]
    amd64/debian Debian is a Linux distribution that's compos ... 4
    ppc64le/debian Debian is a Linux distribution that's compos... 4
    vicamo/debian Debian docker images for all versions/archit... 3
    arm32v5/debian Debian is a Linux distribution that's compos... 2
    s390x/debian Debian is a Linux distribution that's compos... 2
    vpgrp/debian Docker images of Debian. 2
    spritsail/debian-builder A Docker image based on debian:slim ideal fo... 1 [OK]
    dockershelf/debian Repository for docker images of Debian. Test... 1 [OK]
    holgerimbery/debian debian multarch docker base image 1
    fleshgrinder/debian Debian base images for production and multis... 0 [OK]
    casept/debian-amd64 A debian image built from scratch. Mostly fo... 0
    jdub/debian-sources-resource Concourse CI resource to check for updated D... 0 [OK]
    1and1internet/debian-9-nginx-php-7.2-wordpress-4 debian-9-nginx-php-7.2-wordpress-4 0 [OK]
    konstruktoid/debian debian base image 0 [OK]

    
    In the **OFFICIAL** column, the line **OK** shows that the image was built and is supported by the company who developed it. Once the right image has been selected, you can download it to your computer using the **pull** subcommand.  
    
    For example, to download the official ubuntu image to your computer:  
    ``.shell
    docker pull debian  
    

    You will see a similar result:
    ``.shell
    [email protected]:~# docker pull debian
    Using default tag: latest
    latest: Pulling from library/debian
    90fe46dd8199: Pull complete
    Digest: sha256:2857989334428416b1ef369d6e029e912a7fe3ee7e57adc20b494cc940198258
    Status: Downloaded newer image for debian:latest
    docker.io/library/debian: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 13 days ago 73.9MB
    debian latest 3de0e2c97e5c 2 weeks ago 114MB
    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 debian  
    

    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
    e4a123443895 debian "bash" 3 minutes ago Exited (0) About a minute ago
    ac717eb882db hello-world "/hello" About an hour ago Exited (0) About an hour ago bold_lovelace

    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
    e4a123443895 debian "bash" 5 minutes ago Exited (0) 2 minutes ago

    To start a stopped container, use the command **docker start** and give the container id or its name  
    ``.shell
    docker start e4a123443895  
    

    You can now use docker ps to see its status:
    ``.shell
    [email protected]:~# docker ps
    CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
    e4a123443895 debian "bash" 6 minutes ago Up 12 seconds tender_hugle

    To stop a running container, use the command **docker stop** and specify the container id or its name  
    ``.shell
    docker stop tender_hugle  
    

    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 tender_hugle

    **Saving changes to the container in a Docker image**
    
    When you run the container from a Docker image, you can create, modify, and delete files, just like in 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" e4a123443895 test/debian-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 it was based on:  
    ``.shell
    docker images  
    

    You will see a similar result:
    ``.shell
    [email protected]:~# docker images
    REPOSITORY TAG IMAGE ID CREATED SIZE
    test/debian-nodejs latest ef3923c87c69 30 seconds ago 203MB
    root/ubuntu-nodejs latest 412fa0b7f003 2 minutes ago 203MB
    ubuntu latest 1d622ef86b13 13 days ago 73.9MB
    debian latest 3de0e2c97e5c 2 weeks ago 114MB
    hello-world latest bf756fb1ae65 4 months ago 13.3kB
    ```
    In this example debian-nodejs is a new image based on an existing debian image from the Docker Hub.</unknown>