Fix Docker Daemon Not Running

Understanding the Error

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

Fix 1: Start Docker Service

sudo systemctl start docker
sudo systemctl enable docker

# Check status
sudo systemctl status docker

Fix 2: Check User Permissions

# Add your user to docker group
sudo usermod -aG docker $USER

# Log out and back in, or:
newgrp docker

# Test
docker ps

Fix 3: Check Docker Socket

ls -la /var/run/docker.sock
# Should be srw-rw---- root docker

# If missing, reinstall docker
sudo apt install --reinstall docker-ce

Fix 4: Check Service Logs

sudo journalctl -u docker -f
sudo systemctl status docker

# Look for errors like:
# - "failed to start daemon"
# - "iptables failed"

Fix 5: Reset Docker

sudo systemctl stop docker
sudo rm /var/run/docker.pid
sudo systemctl start docker

Fix 6: Reinstall Docker

sudo apt remove docker docker-engine docker.io containerd runc -y
sudo apt update
sudo apt install docker.io -y
sudo systemctl start docker
sudo systemctl enable docker

Fix 7: Docker Desktop (Windows/Mac)

Restart Docker Desktop application or reset to factory defaults.