How to Setup Docker on Ubuntu

Docker uses virtualization technology which in turn makes developing and deploying containerized applications a breeze! Virtualization allows the container to be deployed on any machine without any compatibility issues. So it makes your software simple to develop, deploy, use and maintain. Docker Containers are, however, different from a typical virtual machine in that they act as micro-services, each with specific jobs. Each Docker container runs the operating system on isolated CPU processes, memory and network resources. Because of this, you can be easily added, remove, start and stop it again without affecting the host operating system. Containers usually run one specific task such as MySQL database or Node.js application and network it together to scale them.

Unlike virtual machines, resources are shared directly with hosts this allows you to run many docker containers. Docker uses less disk space as it is able to reuse files using the layered file system.

In this tutorial, we will show you how to setup and use Docker on Ubuntu.

Requirements

Heads up! You will require the following items for you to proceed:

  • A server running Ubuntu 18.04 or 20.04
  • A root password is configured on your server

Install the Required Dependencies

First, you will need to install some dependencies need by Docker in your server. You can install all these dependencies by running the following command:

apt-get install apt-transport-https ca-certificates curl gnupg2 software-properties-common -y

After installing all the required packages, you can proceed to install Docker.

Setup Docker

By default, the latest version of Docker is not available in the Ubuntu default repository. So it is a good idea to install Docker from the official docker repository.

First, download and add the Docker GPG key with the following command:

curl -fsSL https://download.docker.com/linux/ubuntu/gpg | apt-key add -

Next, add the Docker repository using the APT command mentioned below. You can set you architecture to x86_64, amd64, armhf or arm64.

add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"

Once the repository is added, update the repository and install the latest version of the Docker with the following command:

apt-get update -y
apt-get install docker-ce docker-ce-cli containerd.io -y

Now, you can verify the status of the Docker with the following command:

systemctl status docker

You should get the following output once Docker as been setup:

โ— docker.service - Docker Application Container Engine
   Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
   Active: active (running) since Tue 2020-06-16 09:25:58 AEST; 2 months 22 days ago
     Docs: https://docs.docker.com
 Main PID: 3353 (dockerd)
    Tasks: 36
   Memory: 74.4M
   CGroup: /system.slice/docker.service
           โ”œโ”€3353 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

How to Use Docker

The basic syntax of docker command is shown below:

docker [option] [command] [arguments]

You can list all available options with docker by running the following command:

docker

You should see the complete list of docker subcommands in the following output:

Usage:	docker [OPTIONS] COMMAND

A self-sufficient runtime for containers

Options:
      --config string      Location of client config files (default "/home/anthony/.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 "/home/anthony/.docker/ca.pem")
      --tlscert string     Path to TLS certificate file (default "/home/anthony/.docker/cert.pem")
      --tlskey string      Path to TLS key file (default "/home/anthony/.docker/key.pem")
      --tlsverify          Use TLS and verify the remote
  -v, --version            Print version information and quit

Management Commands:
  builder     Manage builds
  config      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

Commands:
  attach      Attach local standard input, output, and error streams to a running container
  build       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
  deploy      Deploy a new stack or update an existing stack
  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
  login       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 an image or a repository from a registry
  push        Push an image or a repository to a registry
  rename      Rename a container
  restart     Restart one or more containers
  rm          Remove one or more containers
  rmi         Remove one or more images
  run         Run a command in a new container
  save        Save one or more images to a tar archive (streamed to STDOUT by default)
  search      Search the Docker Hub for images
  start       Start one or more stopped containers
  stats       Display a live stream of container(s) resource usage statistics
  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      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.

Run ‘docker COMMAND –help’ for more information on a command.

You can also display more information about Docker using the following command:

docker info

You should see the following output:

Client:
 Debug Mode: false

Server:
 Containers: 2
  Running: 1
  Paused: 0
  Stopped: 1
 Images: 9
 Server Version: 19.03.8
 Storage Driver: zfs
  Zpool: rpool
  Zpool Health: ONLINE
  Parent Dataset: rpool/ROOT/ubuntu_yybki6/var/lib
  Space Used By Parent: 3448905728
  Space Available: 946661916672
  Parent Quota: no
  Compression: lz4
 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:
  apparmor
  seccomp
   Profile: default
 Kernel Version: 5.3.0-59-generic
 Operating System: Ubuntu 19.10
 OSType: linux
 Architecture: x86_64
 CPUs: 8
 Total Memory: 7.356GiB
 Name: merlin
 ID: 5YZ2:UZF4:XECY:2HGI:ON4G:BSDU:3TQM:QOFX:MFO6:62L6:24WS:GOYN
 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

Why not run a container now that you have setup Docker? Next we will pull and run an Nginx container.

Pull a Docker Image from the Docker Hub

Docker image is a file built from the instructions or executable version of an application that can be used to execute code in a Docker container. All docker images are stored in the Docker Hub registry. You can pull your desired image from the Docker Hub using the “docker pull” command.

For example, pull the Nginx image from the Docker Hub, run the following command:

docker pull nginx

This will download an Nginx image from the Docker Hub to your local system. Once the download is completed, you should see the following output:

Using default tag: latest
latest: Pulling from library/nginx
bf5952930446: Pull complete 
cb9a6de05e5a: Pull complete 
9513ea0afb93: Pull complete 
b49ea07d2e93: Pull complete 
a5e4a503d449: Pull complete 
Digest: sha256:b0ad43f7ee5edbc0effbc14645ae7055e21bc1973aee5150745632a24a752661
Status: Downloaded newer image for nginx:latest
docker.io/library/nginx:latest

You can list your downloaded image by running the following command:

docker images

You should see all the downloaded images in the following output:

REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
nginx               latest              4bb46517cac3        3 weeks ago         133MB

Run a Docker Container

At this point, you have downloaded Nginx image from the Docker Hub. Now, you will need to run a container from the downloaded image.

There are two ways to run a container.

Run a Docker Container in Interactive Mode

Running a docker container in interactive mode gives you interactive shell access into the container. You can do it using the switch -it as shown below:

docker run -it nginx /bin/bash

This command will brings inside the docker container as shown below:

root@2cc89e08ffb2:/#

Here, you can run any command in the container. For example, run the following command to update the package repository:

root@2cc89e08ffb2:/# apt-get update -y

You can exit from the container with the following command:

root@2cc89e08ffb2:/# exit

Run a Docker Container in Detached Mode

You can run the docker container in detached mode or background using the -d switch. In this mode, you can run any other commands while the container is running.

You can run an Nginx container in detached mode using the following command:

docker run -it -d -p 8080:80 nginx

Once the container is started, you should see the following output:

c135e6f9cb71940d3f033c2d1b5ea21766c86ca9908e0aa21e11f88fe5839302

You can now list the running containers with the following command:

docker ps

You should see your Nginx container in the following output:

CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                  NAMES
1db0b827baa2        nginx               "/docker-entrypoint.โ€ฆ"   17 seconds ago      Up 15 seconds       0.0.0.0:8080->80/tcp   lucid_hofstadter

If you want to connect to your Nginx container, run the following command:

docker exec 1db0b827baa2

Where : 1db0b827baa2 is the id of the Nginx container.

Run a Docker Container with Volume

Volume is used when you want to store the data on the host system and share them across all containers.

First, create a new volume directory on the host system:

mkdir /volume

Next, run the Nginx container and mount the /volume directory to the Nginx container on the /var/www/html directory.

docker run -it -d -v /volume:/var/www/html -p 8080:80 nginx

Next, connect to the Nginx container with the following command:

docker exec -it aba00ef3968b /bin/bash

Then, create a file named test.html inside /var/www/html directory:

touch /var/www/html/test.html

Now, exit from the Nginx container with the following command:

exit

Now, run the following command to list the available files in the /volume directory:

ls /volume

You should see the file named test.html which you have created inside the Nginx container:

test.html

Copy File To and From the Docker Container

The simple and easiest way to copy a file to and from the running container is to use the “docker cp” command.

To copy a file named /etc/hosts from the host system to the Nginx container, run the following command:

docker cp /etc/hosts aba00ef3968b:/opt/

To copy a file named /etc/fstab from the Nginx container to the host system, run the following command:

docker cp aba00ef3968b:/etc/fstab /opt/

Start, Stop and Pause the Container

To stop the Nginx container, run the following command:

docker container stop aba00ef3968b

To start the Nginx container, run the following command:

docker container start aba00ef3968b

You can also pause the Nginx container, using the following command:

docker container pause aba00ef3968b

To stop the all running containers, run the following command:

docker container stop $(docker container ls -aq)

Remove Docker Container

To remove a container, you will need to stop it first.

For example, stop the Nginx container with the following command:

docker container stop aba00ef3968b

Next, remove the Nginx container using the following command:

docker container rm aba00ef3968b

If you want to remove all stoped container, run the following command:

docker container rm $(docker container ls -aq)

Remove Docker Images

To remove the Docker images, list all images in your system with the following command:

docker images

You should see the following output:                                                         

REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
nginx               latest              4bb46517cac3        3 weeks ago         133MB	

Now, remove the Nginx image with the following command:

docker image rm 4bb46517cac3

You should see the following output if image is used by any container:

Error response from daemon: conflict: unable to delete 4bb46517cac3 (cannot be forced) - image is being used by running container 798c8c54736c

In this case, you will need to stop that container then remove the image.

To remove all  unused images in your system, run the following command:

docker image prune -a

You will be asked to confirm before removing image as shown below:

WARNING! This will remove all images without at least one container associated to them.
Are you sure you want to continue? [y/N] y
Deleted Images:
untagged: nginx:latest
untagged: nginx@sha256:b0ad43f7ee5edbc0effbc14645ae7055e21bc1973aee5150745632a24a752661
deleted: sha256:4bb46517cac397bdb0bab6eba09b0e1f8e90ddd17cf99662997c3253531136f8
deleted: sha256:80b21afd8140706d5fe3b7106ae6147e192e6490b402bf2dd2df5df6dac13db8
deleted: sha256:0f04ae71e99f5ef9021b92f76bac3979e25c98d73a51d33ce76a78da6afa9f27
deleted: sha256:9a14852344d88a1fdf8297914729834521ec1c77a27e7e7e394f9c1ef9b87f9d
deleted: sha256:74299126f8099031c5bbd4774147f4ab6b0d0c3afcec774be65d4d07b956752e
deleted: sha256:d0f104dc0a1f9c744b65b23b3fd4d4d3236b4656e67f776fe13f8ad8423b955c

Total reclaimed space: 132.6MB

Conclusion

In the above guide, you learned what Docker is, how to setup Docker and several commands to manage the Docker container. I hope you have now basic knowledge of Docker. You can now explore docker and deploy your application in a containerized environment. Why not practise your Docker skills with your very own NextCloud install using Wasabi S3 as primary storage?



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