I have shown you how to create an Image from a Container using the commit command in the Docker in the previous tutorial. This tutorial will guide you another way without using Container, which is to use a Dockerfile to create a new Image in the Docker. Let’s see how this works!

A Dockerfile is a text file that contains a set of commands to create an image in the Docker. Some of the most commonly used commands in the Dockerfile are listed below:

• FROM <base_image>:<version>: This is a required statement in any Dockerfile. This is used to declare the base Image that we will be building our Image.
• MAINTAINER <author_name>: This statement is used to declare the author of the image, we can declare it or not.
• RUN <command>: We use this command to run a command to install the necessary tools for our Image.
• CMD <command>: In a Dockerfile, we have only one CMD command, which determines the execution rights of the statements when we create new images.
• ADD <src> <dest>: This command is used to copy a local or remote file (declared in <src>) to a location on the container (declared by dest).
• ENV <variable_name>: defines the environment variable in the container.
• ENTRYPOINT <command>: Defines the default command, which will be run when the container is running.
• VOLUME <directory_name>: This is used to link a folder in the Container with the folder on the machine on which we are running Docker.
• EXPOSE <port_number>: used to expose a certain port in the container to the outside.

Some more commands, you can refer to here.

OK, now I will create an example.

I will use Dockerfile to create an image of Ubuntu 16.04 with Git tool installed.

The steps will be as follows:

Firstly, I will create a new Dockerfile file and then open the file.

Then I will add the following lines to my Dockerfile:

Here, I have declared using an Image of Ubuntu with version 16.04.

Then I will run the command:

to update the repositories of this Ubuntu.

Finally, I will declare the Git installation command with the -y option to skip the confirmation step to install Git.

The entire contents of the Dockerfile file are as follows:

Now, we will use this file to create a new image.

The structure of this statement is as follows:

Assuming that I am in the directory containing the Dockerfile file, in my example, the new Dockerfile Image command will look like this:

Result:

Run the apt-get update statement

Install Git

Finish

Check the Images in the Registry of the Docker, you will see the image we just created: