docker: Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running? code example

Example 1: Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

sudo dockerd

Example 2: Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?.

sudo su
systemctl start docker
systemctl enable docker
systemctl restart docker