The solution to the problem that CentOS 7 cannot start after installing Docker

Docker, as a lightweight containerization technology, has become very popular in recent years. CentOS 7 is currently one of the first choices for enterprise-level Linux distributions. However, after installing Docker, some users will encounter the problem of being unable to start Docker. This article will introduce how to solve the problem that CentOS 7 cannot start after installing Docker.

1. Check the running status of Docker

Before starting to solve the problem, you first need to understand the running status of Docker. Open a terminal and enter the following command:

$ sudo systemctl status docker

If the displayed status is active (running), it means Docker is running. If the status is inactive (dead), it means Docker has stopped running.

2. Check the reason why Docker failed to start

If Docker fails to start, you should check the specific error message. You can view the error message through the following command:

$ sudo journalctl -u docker.service

If there is an error message similar to the following, it means that the startup failed:

failed to start docker.service: Unit not found.

The main reason for this situation is that Docker is not installed correctly. , or other versions of Docker already exist in the system.

3. Check Docker installation

If other versions of Docker already exist in the system, they need to be removed. Docker installation can be checked with the following command:

$ yum list installed | grep docker

If another version of Docker is already installed, you need to remove it using the following command:

$ sudo yum -y remove docker-<version></version>

where<version></version> is the Docker version that needs to be deleted, for example: docker-ce-18.06.3.ce-3.el7.x86_64.

4. Update Docker

After removing other versions of Docker, you need to install or update the Docker version. You can update Docker through the following command:

$ sudo yum update docker

If Docker is not installed on the system, you need to use the following command to install Docker:

$ sudo yum -y install docker docker-client docker-client-latest docker-common docker-latest docker-latest-logrotate docker-logrotate docker-selinux docker-engine-selinux docker-engine

The above command will install the latest version of Docker.

After the installation is complete, you need to start Docker:

$ sudo systemctl start docker

5. Other solutions

If none of the above methods can solve the problem, you need to consider the following other solutions Method:

• Check whether the network connection is normal and whether the firewall has set restrictions;
• Restart the operating system, reinstall Docker and configure it.

Summary

After installing Docker, if it cannot be started, it may be because other versions of Docker still exist in the system, causing version conflicts. You need to delete other versions of Docker first and update or install the latest version of Docker. If these methods don't resolve the issue, you need to check other factors such as network connectivity, or consider reinstalling the operating system and Docker.

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