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.

    To search for the desired image, use the following command format:  
    ``.shell
    docker search <имя>  
    

    For example, to search for an nginx image, use the following command:
    ``.shell
    docker search nginx

    This will bring up a list of available images:  
    ``.shell
    [[email protected] ~]# docker search nginx
    NAME DESCRIPTION STARS OFFICIAL AUTOMATED  
    nginx Official build of Nginx.                        13117 [OK]  
    jwilder/nginx-proxy Automated Nginx reverse proxy for docker con... 1791 [OK]  
    richarvey/nginx-php-fpm Container running Nginx + PHP-FPM capable of... 771 [OK]  
    linuxserver/nginx An Nginx container, brought to you by LinuxS... 108  
    bitnami/nginx Bitnami nginx Docker Image 83 [OK]  
    tiangolo/nginx-rtmp Docker image with Nginx using the nginx-rtmp... 70 [OK]  
    alfg/nginx-rtmp NGINX, nginx-rtmp-module and FFmpeg from sou... 58 [OK]  
    jc21/nginx-proxy-manager Docker container for managing Nginx proxy ho... 56  
    nginxdemos/hello NGINX webserver that serves a simple page co... 48 [OK]  
    jlesage/nginx-proxy-manager Docker container for Nginx Proxy Manager 40 [OK]  
    nginx/unit NGINX Unit is a dynamic web and application ... 37  
    nginx/nginx-ingress NGINX Ingress Controller for Kubernetes 30  
    privatebin/nginx-fpm-alpine PrivateBin running on an Nginx, php-fpm &amp; Al... 24 [OK]  
    schmunk42/nginx-redirect A very simple container to redirect HTTP tra... 18 [OK]  
    nginxinc/nginx-unprivileged Unprivileged NGINX Dockerfiles 14  
    centos/nginx-18-centos7 Platform for running nginx 1.8 or building n... 13  
    centos/nginx-112-centos7 Platform for running nginx 1.12 or building ... 13  
    raulr/nginx-wordpress Nginx front-end for the official wordpress:f... 12 [OK]  
    nginx/nginx-prometheus-exporter NGINX Prometheus Exporter 12  
    sophos/nginx-vts-exporter Simple server that scrapes Nginx vts stats a... 7 [OK]  
    mailu/nginx mailu nginx frontend 6 [OK]  
    bitnami/nginx-ingress-controller Bitnami Docker Image for NGINX Ingress Contr... 5 [OK]  
    ansibleplaybookbundle/nginx-apb An APB to deploy NGINX 1 [OK]  
    wodby/nginx Generic nginx 1 [OK]  
    centos/nginx-110-centos7 Platform for running nginx 1.10 or building ... 0  
    
    

    In the OFFICIAL column, the line OK shows that the image is built and supported by the company developing this project. When the desired 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 nginx

    You will see a similar result:  
    ``.shell
    [[email protected] ~]# docker pull nginx
    Using default tag: latest  
    latest: Pulling from library/nginx  
    54fec2fa59d0: Pull complete  
    4ede6f09aefe: Pull complete  
    f9dc69acb465: Pull complete  
    Digest: sha256:86ae264c3f4acb99b2dee4d0098c40cb8c46dcf9e1148f05d3a51c4df6758c12  
    Status: Downloaded newer image for nginx:latest  
    docker.io/library/nginx:latest  
    

    After the image has been downloaded to your server, you can run it using the run option:
    ``.shell
    docker run <имя>

    To view the downloaded images, type ``:  
    ``.shell
    docker images  
    

    You will see a similar result:
    ``.shell
    [[email protected] ~]# docker images
    REPOSITORY TAG IMAGE ID CREATED SIZE
    nginx latest 602e111c06b6 12 days ago 127MB
    centos latest 470671670cac 3 months ago 237MB
    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 displaying a test message. 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 centos  
    

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

    Next, you can run commands inside the container  
    
    Let's install MariaDB:  
    ``.shell
    yum install mariadb-server  
    

    Changes that are executed inside a container apply only 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  
    dadc89ffcb35 centos "/bin/bash" 13 minutes ago Exited (0) 52 seconds ago nifty_jang  
    9ff36f3a478b hello-world "/hello" 45 minutes ago Exited (0) 45 minutes ago naughty_shirley  
    

    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  
    dadc89ffcb35 centos "/bin/bash" 14 minutes ago Exited (0) About a minute ago nifty_jang  
    

    To start a stopped container, use the command docker start and specify the container ID or name
    ``.shell
    docker start dadc89ffcb35

    You can now use **docker ps** to see its status:  
    ``.shell
    [[email protected] ~]# docker ps
    IMAGE ID COMMAND CREATED STATUS PORTS NAMES  
    dadc89ffcb35 centos "/bin/bash" 23 minutes ago Up 38 seconds nifty_jang  
    

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

    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 nifty_jang  
    

    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 as you would on a virtual machine.

    After installing MariaDB in a Centos 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 MariaDB container as the basis for future images.

    Then confirm the changes to 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 the user test and the container ID dadc89ffcb35, the command would look like this:  
    ``.shell
    docker commit -m "added mariadb-server" -a "test" dadc89ffcb35 test/centos-mariadb  
    

    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:
    ``.shell
    docker images

    You will see a similar result:  
    ``.shell
    [[email protected] ~]# docker images
    REPOSITORY TAG IMAGE ID CREATED SIZE  
    test/centos-mariadb latest bd8ad6193efb 29 seconds ago 493MB  
    nginx latest 602e111c06b6 12 days ago 127MB  
    centos latest 470671670cac 3 months ago 237MB  
    hello-world latest bf756fb1ae65 4 months ago 13.3kB  
    
    

    In this example, centos-mariadb is a new image created from an existing centos image from the Docker Hub.