Cannot connect to the Docker daemon · Knowledge & Memory Center

Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?
permission denied while trying to connect to the Docker daemon socket

Checks

SHELL

1systemctl status docker # is the daemon running?

2docker context ls # which endpoint is the CLI using?

3ls -l /var/run/docker.sock # owner should be root:docker

4groups # is your user in the docker group?

5journalctl -u docker -n 50 # why the daemon failed to start

Start it

SHELL

1sudo systemctl start docker

2sudo systemctl enable docker # start on boot

3# Docker Desktop (macOS / Windows): open the app and wait for "Engine running"

Add your user to the docker group

SHELL

1sudo usermod -aG docker $USER

2newgrp docker # or log out and back in

3docker ps # should now work without sudo

!

Members of the docker group have root-equivalent access to the host. Only add trusted users; consider rootless Docker on shared machines.

DOCKER_HOST env var or a stale docker context points somewhere else: unset DOCKER_HOST / docker context use default
Daemon crashes on start because of invalid JSON in /etc/docker/daemon.json
Disk full: the daemon cannot start its data root (see "No space left on device")