**Cannot connect to Docker daemon on Linux host -- all standard fixes failed**

The docker service is running (systemctl status docker shows active), but docker ps consistently returns "Can't connect to the Docker daemon at unix:///var/run/docker.sock: permission denied" or "No such file or directory." I have already tried sudo chmod 666 /var/run/docker.sock, added my user to the docker group with usermod -aG docker $USER (relogged afterward), and restarted both Docker and systemd-cored. The issue persists across reboots. Is there a permission override or AppArmor profile I might be missing?