This tutorial continues Docker related article series and covers the most often used Docker commands. We’re starting a brief Docker overview, then jumping to the installation of Docker to your server. Next, we’ll walk you through all required commands for managing Docker containers, images, and volumes. Become a professional Docker user by following this guide in 10 minutes.

What is Docker

Docker is an open platform for developing, shipping, and running applications. It is the standard de facto for packaging and sharing apps – from desktop to the cloud.

To achieve its goal, Docker is using containers.

The container has the following characteristics:

• A container is a package for the software and all required libraries.
• As soon as is launched, a container determines a runtime environment for your application.
• A container is lighter than a virtual machine, so that it can be launched way faster.
• A container is distributed in the form of an image, which consists of multiple layers. Multiple containers can reuse these layers.

The features above allow you to:

• Build isolated environments for deploying.
• Launch your applications in minutes.

Docker helps you to simplify and automate every step of the software development process.

Here are the essential Docker features:

• Docker has a giant community.
• Docker is a simple and lightweight way of distributing software.
• Docker has a giant public repository of containers for all possible purposes.
• Docker lowers dev and ops costs.
• Docker configuration is straightforward and quick.
• Docker provides application isolation.
• Docker image has layers, which has version control.
• Docker automates every step of container management.

You can install Docker on Linux, macOS, and Windows operating systems.

Install Docker

This section describes how to install the Docker CE (community edition) package on Linux operating system.

If you’re using the AWS cloud, I suggest an article about Docker’s automatic installation to the EC2 instance using CloudFormation.

Install Docker on Ubuntu/Debian

By default, Ubuntu or Debian’s default repository does not contain the latest version of the Docker CE package. So you will need to add the Docker CE official repository to your system.

Before adding the repository, install some required dependencies by running the following command:

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

After installing all dependencies, import the Docker GPG key using the following command;

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

Next, add the Docker CE official repository to the APT source file with the following command:

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

Once the repository has been added, you will need to update the repository cache. You can update it with the following command:

apt-get update -y

Once your repository is up-to-date, run the following command to install the latest version of Docker CE to your system.

apt-get install docker-ce -y

The above command will install the Docker CE package in your system and start the service automatically.

You can verify the installed version of Docker CE by running the following command:

docker --version

You should see the Docker Version in the following output:

Docker version 19.03.13, build 4484c46d9d

If you want to remove the Docker package from your system, run the following command:

apt-get remove docker-ce

Install Docker on CentOS/RHEL

For CentOS or RHEL operating system, you will need to install the Docker CE repo in your system. You can use the DNF command to add and enable the Docker CE repository as shown below:

dnf config-manager --add-repo=https://download.docker.com/linux/centos/docker-ce.repo

Once the Docker CE repository has been added, you can list all available versions of Docker CE by running the following command:

dnf list docker-ce --showduplicates | sort -r

You should get the complete list in the following output:

docker-ce.x86_64                3:19.03.13-3.el8                docker-ce-stable
Docker CE Stable - x86_64                        54 kB/s | 3.8 kB     00:00
CentOS-8 - Extras                                14 kB/s | 8.1 kB     00:00
CentOS-8 - Base                                 4.6 MB/s | 2.2 MB     00:00
CentOS-8 - AppStream                            4.7 MB/s | 5.8 MB     00:01
Available Packages

Next, install the latest version of Docker CE by running the following command:

dnf install docker-ce --nobest

Once the Docker is installed, verify the installed version with the following command:

docker --version

You should get the following output:

Docker version 19.03.13, build 4484c46d9d

To start the Docker service, run the following command:

systemctl start docker

To stop the Docker service, run the following command:

systemctl stop docker

You can also run the following command to display more information on Docker:

docker info

You should see the following output:

If you want to remove the Docker package from your system, run the following command:

dnf remove docker-ce

Managing Containers With Docker

The docker container command is used to manage the container lifecycle. If you do not have the image to run the container from, the Docker will go to the registry, download it.

Run Docker Container

Use the following syntax to download the image from the Docker registry and create a container.

docker container run [your-image-name]

For example, run the following command to create an Apache webserver container:

docker container run httpd

You should get the following output:

You can use the option --rm with Docker run command to removes a container after it exits.

docker container run --rm httpd

Connect To Docker Container Shell

You can use the option -it with Docker run command to create and start the Apache container and attach it to the interactive bash shell.

docker container run -it httpd /bin/bash

You should get the following output:

Launch Docker Container In The Background

You can now run any command inside the container.

You can use the option -td with the Docker run command to create and start the Apache container and keep it running.

docker container run -td httpd

You should get the following output:

Set Up Docker Container Name

You can use the option --name with Docker run command to assign a container name using the following syntax:

docker container run --name [container-name] -td [image-name]

For example, create a new container from the Apache image and assign a name apacheweb with the following command:

docker container run --name apacheweb -td httpd

Bind Docker Container On The Specific Port

If you want to access the external machine’s container process, you can expose a container port to the external network.

In this case, you can use the option -p with the Docker command to expose the specific port as shown below:

docker container run -p [host-port]:[container-port] --name [container-name] -dit [image-name]

For example, create an apache webserver container and expose the container port 80 to port 8080 with the following command:

docker container run -p 8080:80 --name apacheweb -dt httpd

You can now access the apache web server running inside the container using the URL http://localhost:8080.

List All Docker Containers

To list all running and stopped containers in your system, run the following command:

docker ps -a

You should see all containers in the following output:

To list only running containers in your system, run the following command:

docker ps

You can also list the container with the following command:

docker container ls

Display Docker Container Stats

To display the live statistics of the running container (CPU and memory utilization, network and disk I/O) named apacheweb, run the following command:

docker stats apacheweb

You should see the following output:

Display All Docker Container Processes

To list all running processes inside the running container named apacheweb, run the following command:

docker top apacheweb

You should see the following output:

Display Docker Container Logs

To display the logs of the running container named apacheweb, run the following command:

docker logs apacheweb

You should see the following output:

Start, Stop, And Pause Docker Container

To stop the running container named apacheweb, run the following command:

docker container stop apacheweb

To start the container named apacheweb, run the following command:

docker container start apacheweb

To pause the container named apacheweb, run the following command:

docker container pause apacheweb

Restart Or Kill Docker Container

To restart the running container named apacheweb, run the following command:

docker container restart apacheweb

To kill the running container named apacheweb, run the following command:

docker container kill apacheweb

Attach To Already Running Docker Container

To connect to the running container, run the following command:

docker container exec -it apacheweb /bin/bash

To run any command inside the running container, run the following command:

docker container exec -it apacheweb ls

Managing Docker Images

In this section, we will show you some most commonly used commands to manage the Docker image.

Download Docker Image From The Registry

To download or pull the image from the Docker registry, use the following syntax:

docker pull [image-name]

For example, you can pull the Nginx web server image from the Docker registry with the following command:

docker pull nginx

You should get the following output:

Upload Docker Image To The Registry

If you want to upload an existing image to the Docker registry, use the following syntax:

docker push [image-name]

Log in to Docker The Registry

First, you will need to login into the Docker registry with the following command:

docker login

Once login, run the following command to get the id of the Nginx image and tag the image with the following command:

docker images

Output:

REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
nginx               latest              f35646e83998        3 weeks ago         133MB
httpd               latest              3dd970e6b110        3 weeks ago         138MB

Add Tag To Docker Image

Next, tag the image with the following command:

docker tag f35646e83998 amaksimov/nginx

Where:

• f35646e83998 is the image id, amaksimov is the Docker registry name and nginx is the name of the image.

Next, push the Nginx image to the Docker registry with the following command:

docker push amaksimov/nginx

You should see the following output:

Create Docker Image From Running Container

You can also create an image from an existing container using the following syntax:

docker commit [container-name] [new-image-name]

For example, create an image from the Apache container, run the following command:

docker commit apacheweb apache-image

To save your existing image to the tar archive by running the following command:

docker save apache-image > apache-image.tar

History Of The Docker Image

You can print the history of any Docker image with the following command:

docker history apache-image

You should get the following output:

Delete Docker Image

You can remove any Docker image using the following syntax:

docker rmi [image-name]

For example, if you want to remove the Apache image, you will need to stop the container that is using the httpd image:

docker container stop apacheweb
docker rm apacheweb

First, we need to delete apache-image image:

docker rmi apache-image

Only afterward, we remove the httpd image with the following command:

docker rmi httpd

Through time, manually created images and containers may bring some mess to your server. Please take a look at our Docker FAQ to find out how to clean up everything.

Managing Docker Volumes

When you create a new container, store some data, and delete the container, data will be lost. In this case, you can create a volume on the host system and start a container using this volume. After deleting the container, you can retrieve the data from the volume. You can also use Docker volume to share the data between multiple containers.

In this section, we will some most commonly use docker volume commands with examples.

Create Docker Volume

To create a new volume named datavolume with the following command:

docker volume create datavolume

List all Docker Volumes

To list your created volume, run the following command:

docker volume ls

You should see the following output:

Print Docker Volume Information

To print more information about volume, run the following command:

docker inspect datavolume

You should see the following output:

Mount Volume To Docker Container

To create a new container named apacheweb and mount the datavolume on the host system to the /mnt directory to the container, run the following command:

docker run -it --name apacheweb1  --mount source=datavolume,destination=/mnt -td httpd

Remote Docker Volume

To remove the volume, run the following command:

docker volume rm datavolume

Docker FAQ

How to delete unused Docker Images

To delete all unused docker images, you need to run the following command:

docker rmi $(docker images -a -q)

How to remove all exited Docker containers

All exited Docker containers could be removed by running the following command:

docker rm $(docker ps -a -f status=exited -q)

How To Stop And Remove All Docker Containers

To stop all Docker containers, you need to run:

docker stop $(docker ps -a -q)

To delete all stopped Docker containers, you need to run:

docker rm $(docker ps -a -q)

How to delete all unused Docker Images, Containers, Volumes, Networks

To delete all unused Docker resources, you may use the following command:

docker system prune

To delete all Docker resources completely (used and unused), run the following command:

docker system prune -a

Summary

In the above guide, you learned about the most commonly used Docker commands and their usage with examples. I hope this will help you to perform day-to-day tasks.

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• Container Management and Orchestration on AWS