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:

root@kvmde68-19464:~# 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  
root@kvmde68-19464:~# 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:  
root@kvmde68-19464:~# 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
root@kvmde68-19464:~# 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:

root@kvmde68-19464:~# 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:  
root@kvmde68-19464:~# 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:  
root@kvmde68-19464:~# docker run -it ubuntu  

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

root@e83d97af5a32:/# 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

root@kvmde68-19464:~# docker ps  

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

root@kvmde68-19464:~# docker ps  

root@kvmde68-19464:~# 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  

root@kvmde68-19464:~# 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:
root@kvmde68-19464:~# 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:
root@kvmde68-19464:~# 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.

Updated July 30, 2020