6. Docker Image

Docker Image 

        In Docker, everything is based on Images. An image is a combination of a file system and parameters. Let’s take an example of the following command in Docker.

   #docker run hello-world

1. The Docker command is specific and tells the Docker program on the Operating System that something needs to be done.

2.The run command is used to mention that we want to create an instance of an image, which is then called a container.

3. Finally, "hello-world" represents the image from which the container is made.

    Now let’s look at how we can use the CentOS image available in Docker Hub to run CentOS on our Ubuntu machine. We can do this by executing the following command on our Ubuntu machine.

     #sudo docker run centos –it /bin/bash

       Note the following points about the above sudo command:

* We are using the sudo command to ensure that it runs with root access.

*Here, centos is the name of the image we want to download from Docker Hub and install on our Ubuntu machine.

*    ─it is used to mention that we want to run in interactive mode.

*   /bin/bash is used to run the bash shell once CentOS is up and running.

Displaying Docker Images:-

To see the list of Docker images on the system, you can issue the following command.

   #docker images

This command is used to display all the images currently installed on the system.

Return Value

This command is used to display all the images currently installed on the system.

From the above output, you can see that the server has three images: centos, newcentos, and jenkins. Each image has the following attributes:

·     TAG – This is used to logically tag images.

·     Image ID – This is used to uniquely identify the image.

·     Created – The number of days since the image was created.

·     Virtual Size – The size of the image.

Downloading Docker Images:- 

Images can be downloaded from Docker Hub using the Docker run command. Let’s see in detail how we can do this.

Syntax

The following syntax is used to run a command in a Docker container.

#docker run imageName

Return Value

The output will run the command in the desired container.

You will now see the CentOS Docker image downloaded. Now, if we run the Docker images command to see the list of images on the system, we should be able to see the centos image as well.

Removing Docker Images:-

The Docker images on the system can be removed via the docker rmi command. Let’s look at this command in more detail.

#docker rmi ImageID

Docker Images ID :-

This command is used to return only the Image ID’s of the images

#docker images -q

Docker Inspect-

This command is used see the details of an image or container.

#docker inspect Repository

Repository – This is the name of the Image

Example-

#sudo docker inspect jenkins

When we run the above command, it will produce the following result:

For More Details..

https://linuxvmaws.blogspot.com

https://docs.docker.com/engine/reference/commandline/images/