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How to fix “cannot connect to the Docker daemon” Error

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Docker is a powerful platform for building, shipping, and running distributed applications. However, when working with Docker, you may come across an error message that says “cannot connect to the Docker daemon”. This error typically occurs when the Docker daemon is not running or the user running the command does not have permission to connect to the Docker daemon. In this article, we will cover the ways to resolve this error with proper instructions and examples.

First, let’s understand why this error occurs. The Docker daemon is a background process that manages Docker containers and images. When you run a command such as a docker run, it sends a request to the Docker daemon to perform the requested action. If the Docker daemon is not running or the user running the command does not have permission to connect to the Docker daemon, the command will fail and display the “cannot connect to the Docker daemon” error.

Solutions to Resolve Error

Solution 1: Ensure that the Docker daemon is running

The first step in resolving the error is to check if the Docker daemon is running. You can do this by running the below command. If the Docker daemon is running, you will see an output similar to the following output screenshot:

systemctl status docker
Ensuring that docker is running

 

If the Docker daemon is not running, you can start it by running the above command.

Solution 2: Add the current user to the docker group

On Linux systems, the user running the command must be a member of the docker group to connect to the Docker daemon. You can check if the user is a member of the docker group by running the command id. If the output shows that the user is not a member of the docker group, you can add the user to the group by running the below command:

sudo usermod -aG docker $USER
Adding current user in docker group

 

Solution 3: Check the Ownership of used Files

There are several ways to check the ownership of the files used by the Docker daemon on a Linux system. Here are a few methods:

1. Use the ls -l command to view the file ownership and permissions of the Docker socket:

ls -l /var/run/docker.sock
Checking the ownership of used files

 

2. Use the stat command to view the file ownership and permissions of the Docker socket:

stat /var/run/docker.sock
Viewing the ownership and permissions

 

Solution 4: Restart the Docker daemon

There are several ways to restart the Docker daemon on a Linux system, here are a few common methods:

1. Use the systemctl command to restart the Docker service:

sudo systemctl restart docker

2. Use the service command to restart the Docker service:

sudo service docker restart
Restarting Docker daemon

 

Solution 5: Check the status of the Docker daemon:

You can check the status of the Docker daemon by running the command “docker info” or “docker version” in the command line. This will display information about the Docker daemon, including its version number, the number of containers and images running, and the amount of memory and storage it is using. If the daemon is not running, the command will return an error message.

sudo docker info
Checking status of Docker daemon

 

Solution 6: Assign Ownership to the Docker Unix Socket

To assign ownership to the Docker Unix socket, you can use the chown command. The command should be executed as the root user or a user with superuser privileges.

Here is the basic syntax for the command:

sudo chown <user>:<group> /var/run/docker.sock
Assign Ownership to the Docker Unix Socket

 

Replace <user> and <group> with the appropriate user and group to that you want to assign ownership.

Running Docker after resolving the error

Below is an example of how the error message looks like if docker is not running:

$ docker run hello-world
Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

And here is an example of how you can resolve the error by starting the Docker daemon:

$ sudo systemctl start docker
$ docker run hello-world
Hello from Docker!
This message shows that your installation appears to be working correctly.
Successful Docker Execution

 

Conclusion

In conclusion, the “cannot connect to the Docker daemon” error can be caused by several factors such as the Docker daemon not running or the user running the command not having permission to connect to the Docker daemon. By following the steps outlined in this article, you should be able to resolve the error and continue working with Docker.

It’s always a good practice to check the Docker daemon logs for any error messages, it might help you troubleshoot the problem. Additionally, you can refer to the official Docker documentation for more information on troubleshooting this error. Furthermore, you can also join the Docker community, where you can find answers to common problems and ask for help from other experienced users.

In short, to resolve the error “cannot connect to the Docker daemon”, check if the Docker daemon is running, ensure the user has permission to connect to the Docker daemon, restart the machine, run the command with sudo, and check the Docker daemon logs if all above steps fail.



Last Updated : 17 Apr, 2023
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