While using Docker, you need to check if the daemon is running or not in order to diagnose the issues with the container and the docker order.
In this tutorial, you are going to know how to check whether the Docker Daemon or container is running or not.
Check the status using systemctl
Distributions like Debian, Ubuntu, CentOS, and Red Hat use Systemd for service management. In this Systemd there's a Systemctl command, this is a command utility used to examine and control the Systemd and the system manager. You can check whether the Docker daemon is running using the following command -
sudo systemctl status docker
The command will return the status of the docker daemon which will look like this :
Now, check what is being displayed in the "Active". If there is active (running) in green then the Docker daemon and containers should be running.
If there is "inactive" then it indicates that the docker daemon is stopped. you can start it using the following command -
sudo systemctl start docker
If you see the status as "failed" in red then the docker is unable to start due to an error. You can start the Docker daemon in debugging mode to see what's wrong -
sudo dockerd --debug
Inspecting the Process ID file
Whenever the Docker daemon starts, it writes its process ID to /var/run/docker.pid. You can use this process ID to check whether the Docker daemon is running or not.
cat /var/run/docker.pid
You can create various programming scripts using this technique to check the docker daemon's status. When you read the process Id from the file, you can use tools like top which shows the Linux processes to get the information about the docker daemon.
cat /var/run/docker.pid
# when the process id = 1000
top -p 1000
this will return the following information as the output -
You can get the process ID with the "pidof" the command which accepts a process name -
pidof dockerd
#information with top
top -p `pidof dockerd`
If the top matches the dockerd process then the docker daemon is running.
Checking Individual Containers
You can check the status of individual containers, and whether they are running or not. The command docker ps shows the table which contains all the information of the running containers.
docker ps
The output of this command should look like this -
You can combine the docker ps command with the grep keyword to check the status of a specific container by its name or ID. There will be no record if the container is not running.
docker ps | grep container-name
You can start the stopped container using the start command -
docker start container-name
Conclusion
Checking the status of the Docker daemon and the containers is important for diagnosing issues and ensuring that everything is running smoothly in a Docker environment.
In this tutorial, we have learned different ways to check whether the Docker daemon is running, such as using the systemctl command, inspecting the process ID file, and checking the status of individual containers using the docker ps command. By using these methods, you can quickly identify any issues with the Docker environment and take appropriate action to resolve them.
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Frequently Asked Questions
1. How can I check if the Docker daemon is running?
You can check if the Docker daemon is running on Linux-based operating systems by using the systemctl command which checks the status of the Docker daemon: sudo systemctl status docker.
2. How do I check the status of a specific container?
To check the status of a specific container you can use the docker ps command to list all running containers and filter them using grep to show the specific container you're interested in.
3. How do I start a stopped container?
You can start a stopped container using the docker start command followed by the container ID or name. For example, to start a container named "my-container", you can use the command: docker start my-container.
4 Can I use these methods to check if the Docker daemon or container is running on all operating systems?
No, you can not use these methods to check if the Docker daemon or container is running on all operating systems as these methods are specific to Linux distributions. The methods may differ for other operating systems, such as macOS or Windows which you can explore on studytonight.
