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

$ docker ps
CONTAINER ID   IMAGE     COMMAND   CREATED   STATUS    PORTS     NAMES

Happiness!

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

Saddness!

Symptom

You installed Rancher Desktop, and you have setup Ubuntu on your WSL2 environment and then you go to try some docker things and it is not working.

$ type docker
docker is hashed (/mnt/c/Program Files/Rancher Desktop/resources/resources/linux/bin/docker)

But you see sadness.

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

Rancher Desktop > Main Window > Preferences > WSL > Integrations (Tab)

Expose Rancher Desktop's Kubernetes configuration and Docker socket to Windows Subsystem for LInux (WSL) distros
Ubuntu

Hit that check box as fast as you can, and you are off to the races! Hope that helps.