Is Docker started? How to check

Docker is an open source containerization platform that makes application development, testing and deployment easier and more portable. Docker is popular because it allows you to quickly create and run applications without worrying about environmental issues.

However, sometimes the Docker service may not start, which may cause a series of problems. In this article, we will discuss how to check whether Docker is started and solve the problem of Docker startup failure.

How to check if Docker is started?

Docker usually starts automatically after installation. However, sometimes it stops running due to some errors, causing users to be unable to use the Docker service. In this case, we can check whether Docker has been started by the following method.

Method 1: Check the Docker process

The first method is to check whether the Docker process is running. In Linux, we can use the following command to check:

$ ps aux | grep docker

If you can see the following, it means Docker is running:

root 3114 2.0 1.1 376848 23456 ? Ssl Mar28 10:57 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

If you do not see any output, it means Docker is not started. . In this case, we can run the following command to start Docker:

$ sudo systemctl start docker

Method 2: Check the Docker service status

The second method is to check the Docker service status. In Linux, we can use the following command to check the Docker service status:

$ sudo systemctl status docker

If you see the following, it means Docker has started:

● docker.service - Docker Application Container Engine Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled) Active: active (running) since Sat 2019-03-02 09:19:03 EST; 4h 24min ago Docs: https://docs.docker.com Main PID: 995 (dockerd) CGroup: /system.slice/docker.service ├─ 995 /usr/bin/dockerd -H fd:// └─1583 docker-containerd --config /var/run/docker/containerd/containerd.toml Mar 02 09:19:03 docker systemd[1]: Starting Docker Application Container Engine... Mar 02 09:19:03 docker dockerd[995]: time="2019-03-02T09:19:03-05:00" level=info msg="Starting up" Mar 02 09:19:03 docker dockerd[995]: time="2019-03-02T09:19:03-05:00" level=info msg="detected 127.0.0.53 nameserver, assuming systemd-resolved, so using resolv.conf: /run/systemd/resolve/resolv.conf" Mar 02 09:19:03 docker systemd[1]: Started Docker Application Container Engine.

If you see "Active: inactive (dead )" or "Docker application container engine is not installed." output, it means that the Docker service is not started or Docker is not installed.

How to solve the problem of Docker startup failure?

When Docker fails to start, we can try the following methods to solve it:

Method 1: Restart the Docker service

Trying to restart the Docker service can solve some problems caused by temporary failures. question. We can use the following command to restart the Docker service:

$ sudo systemctl restart docker

Method 2: Check the Docker configuration file

In some cases, Docker cannot start due to configuration file problems. We can use the following command to check the configuration file:

$ sudo docker info | grep -i root

If "Docker Root Dir: /var/lib/docker" is output, it means that the Docker root directory exists. If it does not exist, you can use the following command to re-create it:

$ sudo mkdir /var/lib/docker

Method 3: Check the Docker running environment

Sometimes Docker cannot start because it may encounter problems with the container running environment. We can use the following command to check the Docker running environment:

$ docker run hello-world

If the output is similar to the following, it means that the Docker environment is normal:

Unable to find image 'hello-world:latest' locally latest: Pulling from library/hello-world 1b930d010525: Pull complete Digest: sha256:0e11c388b664df8a27c7151b9c54cbb2a2e575fa4bb2b27699eccf6b9e773e12 Status: Downloaded newer image for hello-world:latest Hello from Docker! This message shows that your installation appears to be working correctly.

If "docker: Cannot connect to the Docker daemon at unix" appears :///var/run/docker.sock. Is the docker daemon running" error means that Docker cannot connect to the Unix socket. At this time we can use the following command to restart the Docker service:

$ sudo service docker restart

Summary

It is very important to check whether Docker is started, because Docker is often indispensable in application development, testing and deployment One of the tools. In this article, we provide two methods to check whether Docker is started, and also introduce three common methods to solve the problem of Docker startup failure. Whether you're a Linux system administrator or just starting out with Docker, this article is packed with helpful tips and advice.

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