You’re running a
docker command like
docker ps, but you only see this error message:
Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?
As the error message already tells you, the
docker daemon is currently not running.
On Ubuntu (16.04 upwards) and many other
systemd-based distributions, you can fix this by
sudo systemctl start docker
In most cases, you want to automatically start the docker daemon at boot. In order to do this, run
sudo systemctl enable docker
After that, run your command (e.g.
docker ps) again.