Introduction

When working with Docker images and containers, one of the basic features is committing changes to a Docker image. When you commit to changes, you essentially create a new image with an additional layer that modifies the base image layer.

In this tutorial, learn how to commit changes to a Docker image by following our simple example.

tutorial on how to commit changes to a docker image and saving container to image

Prerequisites

  • Access to a command-line/terminal window (Ctrl+Alt+T)
  • A user account with root or sudo privileges
  • Docker installed and configured

Steps For Committing Changes to Docker Image

Step 1: Pull a Docker Image

To illustrate how to commit changes, you first need to have an image to work with. In this article, we work with the latest Ubuntu image for Docker. Download the image from Docker’s library with:

sudo docker pull ubuntu

docker command to download ubuntu image
If you recheck the available images, you will see the Ubuntu image:

sudo docker images

see docker images on system
Copy IMAGE ID for later use.

Step 2: Deploy the Container

Add the IMAGE ID to the command that will create a container based on the image:

sudo docker run -it cf0f3ca922e0 bin/bash

The –it options instruct the container to launch in interactive mode and enable a terminal typing interface. Upon executing the command, a new container launches and moves you to a new shell prompt for working inside of it.

docker command to run ubuntu image into a container

Step 3: Modify the Container

Now that you are in the container, you can modify the image. In the following example, we add the Nmap software for network discovery and security auditing:

apt-get install nmap

The command will download the Nmap package and install it inside the running container.

install nmap in ubuntu docker container
You can verify the installation by running:

nmap --version

The output shows you that Nmap version 7.60 is installed and ready to use.

how to check nmap version
Once you finish modifying the new container, exit out of it:

exit

Prompt the system to display a list of launched containers:

sudo docker ps -a

You will need the CONTAINER ID to save the changes you made to the existing image. Copy the ID value from the output.

command to list docker containers

Step 4: Commit Changes to Image

Finally, create a new image by committing the changes using the following syntax:

sudo docker commit [CONTAINER_ID] [new_image_name]

Therefore, in our example it will be:

sudo docker commit deddd39fa163 ubuntu-nmap

Where deddd39fa163 is the CONTAINER ID and ubuntu-nmap is the name of the new image.

docker command to commit changes to image
Your newly created image should now be available on the list of local images. You can verify by checking the image list again:

sudo docker images

seee newly commited image in docker

Conclusion

After reading this article, you should now know how to commit changes to a Docker image and create a new one for future use.