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


    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:
    docker [option] [command] [arguments]

    To see all available subcommands, type:  

    The complete list will look like this:

    [email protected]:~# docker  
    Usage: docker [OPTIONS] COMMAND  
    A self-sufficient runtime for containers  
          --config string Location of client config files (default "/root/.docker")
      -c, -context string Name of the context to use to connect to the daemon
                               (overrides DOCKER_HOST env var and default context set with
                               "docker context use")
      -D, --debug Enable debug mode
      -H, -host list Daemon socket(s) to connect to
      -l, --log-level string Set the logging level ("debug"|"info"|"warn"|"error"|"fatal")
                               (default "info")
          --tls Use TLS; implied by --tlsverify
          --tlscacert string Trust certs signed only by this CA (default
          --tlscert string Path to TLS certificate file (default "/root/.docker/cert.pem")
          --tlskey string Path to TLS key file (default "/root/.docker/key.pem")
          --tlsverify Use TLS and verify the remote
      -v, --version Print version information and quit
    Management Commands:  
      builder Manage builds
      configage Manage Docker configs
      container Manage containers
      context Manage contexts
      engine Manage the docker engine
      image Manage images
      network Manage networks
      node Manage swarm nodes
      plugin Manage plugins
      secret Manage Docker secrets
      service Manage services
      stack Manage Docker stacks
      swarm Manage Swarm
      system Manage Docker
      trust Manage trust on Docker images
      volume Manage volumes
      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
    Run 'docker COMMAND --help' for more information on a command.

    To see the options for using a particular command, type:
    docker docker-subcommand --help

    To view all the information about Docker, you can use the command:  
    docker info  
    [email protected]:~# docker info  
     Debug Mode: false
     Containers: 0
      Running: 0
      Paused: 0
      Stopped: 0
     Images: 0
     Server Version: 19.03.11
     Storage Driver: overlay2
      Backing Filesystem: extfs
      Supports d_type: true
      Native Overlay Diff: true
     Logging Driver: json-file
     Cgroup Driver: cgroupfs
      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:
       Profile: default
     Kernel Version: 5.4.0-37-generic
     Operating System: Ubuntu 20.04 LTS
     OSType: linux
     Architecture: x86_64
     CPUs: 1
     Total Memory: 981.3MiB
     Docker Root Dir: /var/lib/docker
     Debug Mode: false
     Experimental: false
     Insecure Registries:
     Live Restore Enabled: false

    Working with Docker images

    By default, Docker gets images from the Docker Hub, 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:
    docker run hello-world

    The correct result of this command, which means that Docker is working correctly, is shown below:  
    [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:d58e752213a51785838f9eed2b7a498ffa1cb3aa7f946dda11af39286c3db9a9  
    Status: Downloaded newer image for hello-world:latest  
    Hello from Docker!  
    This message shows that your installation appears to be working correctly.  
    To generate this message, Docker took the following steps:  
     1. The Docker client contacted the Docker daemon.
     2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
     3. The Docker daemon created a new container from that image which runs the
        executable that produces the output you are currently reading.
     4. 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 ID:
    For more examples and ideas, visit:

    Initially, Docker could not 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.
    docker search debian

    The script looks through the Docker Hub and returns a list of all images whose names match the given search
    [email protected]:~# docker search debian  
    ubuntu Ubuntu is a Debian-based Linux operating sys... 11031 [OK]  
    debian Debian is a Linux distribution that's compos... 3521 [OK]  
    arm32v7/debian Debian is a Linux distribution that's compos... 66  
    itscaro/debian-ssh debian:jessie 28 [OK]  
    arm64v8/debian Debian is a Linux distribution that's compos... 23  
    samueldebruyn/debian-git a minimal docker container with debian and g... 22 [OK]  
    multiarch/debian-debootstrap multiarch ports of debian-debootstrap 12  
    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]  
    ppc64le/debian Debian is a Linux distribution that's compos... 4  
    amd64/debian Debian is a Linux distribution that's compos... 4  
    smartentry/debian debian with smartentry 4 [OK]  
    vicamo/debian Debian docker images for all versions/archit... 3  
    s390x/debian Debian is a Linux distribution that's compos... 2  
    vpgrp/debian Docker images of Debian.                        2  
    arm32v5/debian Debian is a Linux distribution that's compos... 2  
    spritsail/debian-builder A Docker image based on debian:slim ideal fo... 1 [OK]  
    holgerimbery/debian debian multarch docker base image 1  
    dockershelf/debian Repository for docker images of Debian. Test... 1 [OK]  
    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 **OK** line shows that the image was built and is supported by the company who built it. 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:  
    docker pull debian  

    You will see a similar result:

    [email protected]:~# docker pull debian  
    Using default tag: latest  
    latest: Pulling from library/debian  
    e9afc4f90ab0: Pull complete  
    Digest: sha256:46d659005ca1151087efa997f1039ae45a7bf7a2cbbe2d17d3dcbda632a3ee9a  
    Status: Downloaded newer image for debian:latest

    After downloading the image you can start the container with the downloaded image with the run subcommand

    To view the downloaded images, type:
    docker images

    You will see a result like this:  
    [email protected]:~# docker images  
    ubuntu latest 74435f89ab78 6 days ago 73.9MB  
    debian latest 1b686a95ddbf 2 weeks ago 114MB  
    hello-world latest bf756fb1ae65 5 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:
    docker run -it ubuntu

    The command line will show that we are working in the container:  
    [email protected]:~# docker run -it ubuntu  
    [email protected]:/#  

    Next you can run commands inside the container
    apt update

    Install Node.js:  
    apt install nodejs  

    This command installs Node.js in a container from the official Ubuntu repository

    Check that Node.js is installed:
    node -v

    [email protected]:/# node -v  

    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:
    docker ps

    [email protected]:~# docker ps  

    To see the active and inactive containers, run docker ps with option -a:
    docker ps -a

    [email protected]:~# docker ps  

    [email protected]:~# docker ps -a
    2d3ef7e60d67 debian "bash" 23 seconds ago Exited (0) 14 seconds ago crazy_davinci
    e83d97af5a32 ubuntu "/bin/bash" 7 minutes ago Exited (0) 3 minutes ago amazing_wilson
    56aac1efc3f6 hello-world "/hello" 20 minutes ago Exited (0) 20 minutes ago vigorous_allen

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

    [email protected]:~# docker ps -l
    2d3ef7e60d67 debian "bash" 53 seconds ago Exited (0) 43 seconds ago crazy_davinci

    To start a stopped container, use the command **docker start** and give the container id or its name  
    docker start 2d3ef7e60d67  

    You can now use docker ps to view its status:
    [email protected]:~# docker ps
    2d3ef7e60d67 debian "bash" 2 minutes ago Up 31 seconds crazy_davinci

    To stop a running container, use the command **docker stop** and specify the container id or its name  
    docker stop crazy_davinci  

    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.
    docker rm crazy_davinci

    **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 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  
    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 the user test and the container ID 2d3ef7e60d67, the command would look like this:
    docker commit -m "added Node.js" -a "test" 2d3ef7e60d67 test/ubuntu-nodejs

    After confirming (commit) the image, 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:  
    docker images  

    You will see a similar result:
    [email protected]:~# docker images
    test/ubuntu-nodejs latest 79fbfd36b4b3 12 seconds ago 114MB
    ubuntu latest 74435f89ab78 6 days ago 73.9MB
    debian latest 1b686a95ddbf 2 weeks ago 114MB
    hello-world latest bf756fb1ae65 5 months ago 13.3kB
    In this example, ubuntu-nodejs is a new image created from an existing ubuntu image from the Docker Hub.