docker: Cannot connect to the Docker daemon at unix:///var/run/docker.sock. How to deal with this problem?

The error message you are seeing usually occurs when the Docker daemon is not running or the current user does not have the necessary permissions to access the Docker daemon. Here are a few steps you can try to resolve this issue:

1. Check if the Docker daemon is running: You can use the following command to check the status of the Docker daemon:

   sudo systemctl status docker

If it is not running, you can start it using:

   sudo systemctl start docker

2. Verify user permissions: Ensure that the current user has the necessary permissions to access the Docker daemon. By default, the Docker daemon requires root or sudo privileges. You can add your user to the `docker` group to grant it permission to access Docker without using `sudo`. Use the following command to add your user to the `docker` group:

   sudo usermod -aG docker $USER

After running this command, you need to log out and log back in for the changes to take effect.

3. Check Docker socket permissions: Make sure that the Docker socket file has the correct permissions. Run the following command to verify:

   ls -l /var/run/docker.sock

The output should show that the file is owned by the `root` user and the `docker` group. If not, you can change the ownership using:

   sudo chown root:docker /var/run/docker.sock

4. Restart Docker: After making any changes, restart the Docker service to apply the modifications:

   sudo systemctl restart docker

If none of these steps resolve the issue, there might be other underlying problems. Feel free to provide more details or error logs for further assistance.