How to run docker image

Docker is a popular containerization technology that helps developers build, deploy, and run software applications more easily. In this article, we’ll take a deep dive into how Docker works and how to use Docker to run containers.

1. Docker operating principle

Docker uses an important function of the Linux kernel - a feature called cgroups to implement containerization. By using cgroups, Docker can allocate system resources (such as CPU, memory, etc.) to containers and ensure that each container can only access its allocated resources. This can prevent one container from occupying too many system resources and endangering the operation of other containers.

The basic components that Docker runs include images, containers and warehouses. An image is the file system necessary for a container to run and contains all applications and related dependencies. A container is a running instance of Docker, which contains everything needed to run the image, including the file system, environment variables, and startup commands. A repository is a place where Docker images are stored and shared, similar to a Git repository.

2. Docker running steps

1. Get the Docker image

Before using Docker to run a container, you must first obtain a Docker image. You can download it through Docker Hub or use a custom image you made yourself.

2. Create a Docker container

Once an image exists, you can use the image to create a Docker container. Use the docker run command to create and run a Docker container, for example:

docker run -d centos /bin/sh -c "while true;do echo hello world;sleep 1;done"

This command will create a container from the centos image and run an infinite loop of commands in it: output the hello world string and perform one second wait. The -d flag indicates that the container should run in the background.

3. View Docker containers

You can use the docker ps command to view the currently running Docker containers. For example:

docker ps

This command will list all currently running containers.

4. Enter the Docker container

If you need to enter a Docker container, you can use the docker exec command, for example:

docker exec -it container_name /bin/bash

The -it flag means To enter an interactive shell. /bin/bash is the command that will be run.

5. Stop Docker container

You can use the docker stop command to stop a Docker container.

docker stop container_name

This command will stop the container named container_name.

3. Summary

Docker can greatly simplify the deployment and operation of software applications. By understanding the principles and steps of Docker operation, developers can better understand the working mode of Docker and thus better utilize Docker to containerize applications. Therefore, learning Docker is one of the must-have skills for every developer.

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