What The Heck Is Docker? Is It Good For Me?

Many people talk about Docker these days. But most of them are hard to understand because people made it sounds too complicated. Today, I want to explain what Docker is in a simple way. Then I’m going to expand into why we should use it, and what are the use cases.

Docker in One Sentence

Docker is a technology that lets you quarantine an application in a tiny version of a Linux virtual machine and runs your applications.

Why You Should Use Docker?

Code Runs The Same in All Environments

Remember the last time when your code works at your local machine but doesn’t work when it’s deployed to the server? By using Docker, this kind of moment will become history. You can put all your applications with the dependency configured in one package(a.k.a. a Docker image). No matter what environment you’re running your application, all the dependents will be created exactly the same. There will be no more “it works at my local but doesn’t work on the server” moments. Isn’t it awesome?

Docker is Really Fast

Imagine you need to setup a virtual machine, how long does it really take? An hour? Thirty minutes? Docker can do that within seconds. Yeah, you heard me rights. Not minutes, but seconds!

For example, if you want to create a Debian Buster environment. Your only need to run two commands. One to download the Debian Docker image to your machine. This part only needs to be done once. Next, run that image with Docker. Just within a few seconds, you can have a fully functional Debian system running. Check out the following video.

Here’s an example of me running an instance of the Debian container from Ubuntu

Did you see how fast it is?

Code Quarantines

That’s right. Your code is quarantined inside a Docker container(I will explain what is a Docker image below). That means you can run an application using Node.js 14.2.0, a different application on 12.12.0, and another one on (if you really want)8.17.0, all in the same machine! The best part is, they won’t affect each other.

Potentially Saves Money

Back in the day, when we need different environments we need to create a new physical server and set up the OS. Now you can install multiple virtual machines with different OS in them. Docker is similar to a virtual machine. But with fewer overheads. Because Docker containers share the same resources, such as the Linux kernel. In the example of running multiple applications with different dependent versions of a framework, you don’t need to buy another virtual machine. Instead, you can put everything in the same virtual machine and run your application via Docker. If you have 10 virtual machines running 10 different environments, you can now do all of that in one machine. Of course, if your applications need to process a lot of data you’ll still need a different machine. But you got the idea.

So, what is Docker really?

Difference between virtual machines and Docker

Just like most computer applications, Docker runs on top of an operating system. We called this “Docker application” Docker. It mediates between the operating system and the tiny version of operating systems that runs on it. The difference between a virtual machine and Docker is that a virtual machine emulates the infrastructure of a computer. For example, CPU, memory, hard disk, etc. When we install an operating system on a virtual machine, it emulates the whole thing.

On the other hand, Docker runs on the Linux operating system. It shares what’s already running on the operating system and shares the resources with the tiny operating systems (Docker containers) that are run on top of it. For example, if your operating system is Ubuntu and you want to run a Debian container. Docker will share the kernel between Ubuntu and the Debian container. Therefore, instead of installing and running the full Debian operating system, you only need a minimal bit of Debian on top of Docker. It doesn’t need to emulate the infrastructure and spin up the whole operating system again. That’s why one of the reasons Docker is so fast.

Docker Image

Now we know that Docker can run a tiny version of a Linux operating system. How does Docker know what should be in each tiny operating system? That is a Docker image. If we just want to run a tiny version of Ubuntu, we’ll still need an image of Ubuntu. That’s a Docker image.

But that’s just the basics. The best part is, you can copy files from the outside to the image and build a new image. You can even host an application and expose specific ports of the tiny Linux. Sounds familiar? Yes, it works just like any virtual machine (but without a graphics interface) and takes much fewer resources from the host operating system.

Docker Container

A Docker container is nothing but a running instance of a Docker image. You can define what goes into a Docker image. For example, an operating system, dependency packages, your application, and so on. Once you run your Docker image, Docker will create an instance of your Docker image as a Docker container.

I have a post about How to Run Docker on Your old Raspberry Pi. That will give you some ideas of how Docker works in action.

If my note helped, please consider buying me a coffee😁.



How to Run Docker on Your Raspberry Pi in 2020


I wanted to learn about Docker. But I don’t want to keep Docker running on my daily drive machine. It happens that I have an old Raspberry Pi 1 Model B+, which I have bought a long time ago, that just sits there doing nothing. So I decided to make it work for me.

The setup

Here’s my plan:

  1. Install Raspberry Pi OS (previously called Raspbian) on my Raspberry Pi
  2. Install Docker
  3. Run Hello World Container
  4. Remove Docker Image

Step 2 – Install Docker

Yes. I’m skipping step 1 here because there is a very detailed setup guide on Raspberry Pi’s website already. I want to focus on the installation of Docker, so I’m not going to repeat it here.

I have followed a few blog posts. Here are the most optimized steps that I found:

0. Login to your Raspberry Pi OS either directly log in through the terminal or remotely login by SSH. Then you should be on this screen:

Note that the top right hand corner says armv6l

1. Update and upgrade your apt-get package tool

sudo apt-get update && sudo apt-get upgrade

2. Download Docker installation script

curl -fsSL -o

3. Execute the installation script

After the download step above. Check that the script is actually downloaded to your machine:

You should see a file called is downloaded at your current path

Okay, now we can execute the installation script as root user:

sudo sh

Depending on your internet speed, this step will take a few minutes. Sometimes you would think that your Raspberry Pi is frozen. But give it a good couple of minutes. If it runs successfully, you should see the following on your screen:

4. Add a non-root user to the Docker group

sudo usermod -aG docker [your-user]

This step is to add a user to the Docker user group. If you don’t follow this step, you’ll have to run the docker command as a root user. That means you have to type “sudo” every time you run the docker command. Note that you have to replace [your-user] with your actual user name in the command. For example, my user is pi:

sudo usermod -aG docker pi

The “-a” flag is to add anyone of the group to a supplementary group. In this case, the docker group. We should only use it with the -G option. The “-G” flag is to add a supplementary group. Note that “-G” is case sensitive.

When using the “-G” flag alone, if the user is currently a member of a group that is not listed, the user will be removed from the group. This behavior can be changed via the “-a” option, which appends the user to the current supplementary group list.

5. Check your Docker version

The purpose of this step is not just checking your docker version. It also see if your user is actually successfully added to the docker group. If it works, you shouldn’t need to run the docker command as root. i.e. “sudo”

docker version

If you see a “permission denied” message like I did, do NOT run “sudo chmod 666 /var/run/docker.sock”. This command will give read and write permission to the docker.sock file to every user in the system. As Dave H has mentioned, it will cause a security risk.

Run the following command instead:

sudo chown $USER /var/run/docker.sock

The above command changes the ownership of the docker.sock file to your user. If you run the “docker version” command now, the “permission denied” message should be gone.

Now run the following command:

docker info

and here’s my screenshot:

3. Run Docker Hello World container

If you have a Raspberry Pi 2 or newer, you should be able to run the following command for hello-world without any issue.

docker run hello-world

But for older Raspberry Pi, it doesn’t work anymore. My Raspberry Pi 1 Model B+ for example, doesn’t print the hello-world message like when you run hello-world in other systems. You can check the status of the current docker containers using the following command:

docker ps -a

You’ll see that the hello-world container is excited with code 139. It means the container received a segmentation fault.

After some digging on the internet. I realized that it is not the problem of my installation.

Remember in step 0 when you logged in? The message “armv6l” (the letter after the character “6” is not the number one, it’s the letter “L”) actually indicates the instruction set architecture of this particular model of Raspberry Pi. Although the regular hello-world image works in most cases, somehow the latest version of the hello-world either doesn’t support the armv6 instruction set anymore.

To run any docker image on Raspberry Pi OS, the image have to be built on the same architecture. Here’s the version of Hello World Docker image that works:

docker run --name [myHelloWorld] arm32v5/hello-world

[myHelloWorld] is an arbitrary name that you can give to a container. I’ve named mine as “test”. So mine was:

docker run --name test arm32v5/hello-world

Now you will see a normal Hello World message as the following:

There you go! Now you have successfully get Docker running on your old Raspberry Pi 1 Model B+!

4. Remove Docker Image

To remove a Docker image, you have to first remove the docker container. First, list all the Docker containers:

docker ps -a

You should see a list of Docker containers that have been run. Here’s one way to remove a container. To remove the Hello World container above, for example, you can run:

docker rm test

Now if you run docker ps -a again, the list will be empty.

Then, let’s list the available docker images:

docker image ls

You should see the arm32v5/hello-world image. Let’s remove it:

docker image rm arm32v5/hello-world

I’ve also created a Hello World from my Raspberry Pi. Feel free to try it out.

docker image rm lokarithm/armv6-hello-world

Additional Note

As you may have noticed, you can only run Docker images with armv6 instruction sets(or below) on Raspberry Pi 1 and Pi Zero. To find out whether an image support armv6, you can go to Dock Hub to find the image. For example, I want to run an image of Nginx. I would scroll down to the quick reference section:

Find the supported architecture “arm32v6”

From there, if you see “arm32v6” then click on the link. That means you can pull that image and use it on your Raspberry Pi 1 or Zero.

This is the image we need

In the example of Nginx, you can download the image with the following command:

docker pull arm32v6/nginx:stable-alpine

Note: Usually, if you don’t specify the version of the image, Docker will pull the latest version with a tag called “latest”. But in this case, the latest version is tagged as “stable-alpine” instead. I found the correct version by clicking the tags tab on the page. It should work if you use the same version.

Click on the “Tags” tab to list all the available versions of the image

And then run it:

docker run -p 8080:80 arm32v6/nginx:stable-alpine
You should see messages like the above from your screen

The -p flag simply map port 8080 of the host to port 80 of the image. Now you should be able to browse the default Nginx homepage. If you’re running the command directly from the pi, simply open http://localhost:8080. If you’re like me, who SSH into the pi. You can simply use the same local IP address of your Pi to browse the site. In my case

It’s that simple. Happy Docker-ing!

Feel free to leave me a message if you have any question.

If my note helped, please consider buying me a coffee😁.


Side note: I started this post using Putty on Windows 10 to SSH into my Raspberry Pi at the beginning. After a few weeks, I’ve switched to Linux and used Remmina for SSH. So the styling of my screenshots has changed a little.


How To Completely Remove Docker From Your Debian Based Linux

This is a simple note to myself of how to remove Docker from Ubuntu or Raspberry Pi OS (previously called Raspbian). Credit goes to Mayur Bhandare on Stack Exchange. I also added some explanation to some of the commands so you will have a better understanding of what they’re doing.

1. Identify which Docker package have you installed
dpkg -l | grep -i docker
For example, I’ve installed docker-ce and docker-ce-cli

The dpkg command is a package management command in Debian. Just like apt-get in Ubuntu, a Linux distro based on Debian. Since Raspberry Pi OS is also a descendant of Debian, this will work just fine. The above command is basically saying, give me a list of packages that contains the word “docker” in them.

2. Remove the packages

For me, I’ve only installed docker-ce and docker-ce-cli. So I will run the following commands.

sudo apt-get purge -y docker-ce docker-ce-cli
sudo apt-get autoremove -y --purge docker-ce docker-ce-cli

If you have more docker packages installed, you can add those packages names to the end of the commands above. For example:

sudo apt-get purge -y docker-engine docker docker-ce docker-ce-cli
sudo apt-get autoremove -y --purge docker-engine docker docker-ce 

The “-y” flag here is to answer “yes” to the command prompt when it asks you whether to remove a package. You can choose to remove the “-y” flag. Then you’ll see prompts like the following and you have to manually answer yes or y for every package.

3. Remove all the Docker related files

After that, you might want to remove all the Docker images, containers, volumes, and configurations. This is how:

sudo rm -rf /var/lib/docker /etc/docker
sudo rm /etc/apparmor.d/docker
sudo groupdel docker
sudo rm -rf /var/run/docker.sock

The “-rf ” flag is a combination of the “-r” and “-f” flags. “-r” means recursive. So the rm command can remove all the children folders and files of the target folder recursively. “-f” means force. It will ignore non-existent files, and never prompt before removing them. Be careful when you use these two flags together.

The groupdel command is to delete an existing docker user group.

Bonus: Deactivate Network Interface and Ethernet Bridge

If you want to take one step further, you can deactivate the docker0 network interface and delete the docker0 ethernet bridge. Here’s how(Credit: Thanks to anony for mentioning that!😁):

To disable docker0 network interface:

sudo ifconfig docker0 down

To delete the existing docker0 ethernet bridge:

sudo ip link delete docker0

The brctl command is deprecated. Updated the above command. Credit to Nicolas Raoul and SΓΈren (Edited on 2024-03-26)

Congratulations! You have just completely removed Docker from your system!

If my note helped, please consider buying me a coffee😁.