The cause:

After examining your program, I found that you are trying to access the Docker service, but it is not active. This is the reason why you get the error: ”Cannot connect to the docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?”

Solution:

The best solution for this error is starting Docker using service.

If you use the package manager to set up the Docker, a Docker service will be created. It gets easier to manage the Docker. Now let’s use the systemctl service command to start the Docker:

$ systemctl start docker

You can check your program when using Docker by the following command:

$ systemctl status docker
docker.service - Docker Application Container Engine
Loaded: loaded (/usr/lib/systemd/system/docker.service; disabled; vendor preset: disabled)
Active: active (running) since Thu 2022-02-17 19:14:51 UTC; 1min 38s ago
Docs: https://docs.docker.com
Main PID: 1831 (dockerd)
Tasks: 8
Memory: 126.5M
CGroup: /system.slice/docker.service
└─1831 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

You can see that the current program with Docker service is running and the error: ”Cannot connect to the docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?” does not exist.