Discuss solutions to common docker startup image error problems

Docker is a popular containerization technology widely used to build, publish, and run applications. However, during the process of running the Docker image, you may encounter errors when starting the image. This article will discuss common Docker startup image error problems and solutions.

1. Docker startup image error reporting classification

Docker startup image error reporting can be divided into three situations, namely, image does not exist error, startup failure error and port occupation error.

1. Mirror does not exist error

As shown in the figure below, when we try to run a Docker image that does not exist, an error that the image does not exist will appear:

2. Startup failure error

During the container startup process, the startup may fail due to various reasons. For example, the environment variable configuration is incorrect, the command format is incorrect, etc. The following is an example of startup failure:

3. Port occupation error

Docker container needs to bind a port to provide services, but if the port is already occupied by other services, the container Just can't start. The picture below is an error report of a port occupation:

2. Solution to the error report when Docker starts the image

1. Solution to the error report that the image does not exist

If it occurs If the image does not exist, we need to check whether the image name and label are entered correctly. You can check the image list by running the following command:

docker images

If the image does not exist, you need to download the image from Docker Hub or a private repository first. For example, you can use the following command to download the Ubuntu image:

docker pull ubuntu

2. Startup failure error solution

If the container fails to start, we need to find the error based on the error message.

For example, if the container fails to start, we can first use the following command to view the container's log:

docker logs [container_name_or_id]

The error information can be found by viewing the log. Common solutions include:

• Confirm the correctness of the environment variables;
• Confirm whether the command format is correct;
• Confirm whether the internal port of the container is correct;
• Check whether the Dockerfile file is correct, etc.

Prescribe the right medicine according to the error message, modify the configuration or adjust the container parameters, and restart the container.

In addition, you can also use the healthcheck command provided by Docker to check the health status of the container. For example, add the following command to the Dockerfile:

HEALTHCHECK --interval=5m --timeout=3s \
  CMD curl -f http://localhost/ || exit 1

3. Port occupancy error solution

Port occupancy error may be the most common problem. We can use the following command to check the port occupation:

sudo lsof -i :[port_number]

If it is already occupied, you need to close the process occupying the port. If the process occupying the port is a Docker container, you can use the following command to kill the container process:

docker kill [container_id]

If the port is not occupied by other processes, it may be that the Dockerfile or the port definition of the startup command is incorrect. You can use the following command to view the port mapping inside the container:

docker port [container_name_or_id]

Check whether the port is correctly mapped to solve the problem.

3. Summary

This article discusses common situations and solutions for Docker startup image errors. When you encounter an error when Docker starts the image, you can first troubleshoot the error, and then prescribe the right medicine based on the error message to finally solve the problem. At the same time, when using Docker images, you should also pay attention to choosing a stable image version and avoiding port conflicts to ensure the normal operation of the container.

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