How to fix Error starting daemon: error initializing graphdriver: driver not supported in Docker

First, examine the exact error message to understand which storage driver is failing:

# Check systemd journal for Docker daemon errors
sudo journalctl -u docker.service -n 50 --no-pager

# Or try starting dockerd directly to see the full error
sudo dockerd --debug

Look for messages like:
- "prior storage driver aufs failed"
- "driver not supported"
- "/var/lib/docker contains several valid graphdrivers"

If you recently performed a system update, the kernel may have been upgraded but not yet loaded:

# Check if a reboot is required
ls /var/run/reboot-required 2>/dev/null && echo "Reboot required"

# Reboot the system
sudo reboot

After rebooting, try starting Docker again:

sudo systemctl start docker
docker version

Verify which storage drivers your kernel supports:

# Check for overlay/overlay2 support
lsmod | grep overlay
modprobe overlay  # Try loading the overlay module

# Check kernel config for storage driver support
grep -i overlay /boot/config-$(uname -r) 2>/dev/null || \
  zcat /proc/config.gz 2>/dev/null | grep -i overlay

# Check for AUFS support (deprecated in newer kernels)
grep -i aufs /proc/filesystems

Modern systems should use overlay2 as the default storage driver.

Check if multiple storage driver directories exist:

ls -la /var/lib/docker/

If you see multiple directories like aufs, overlay2, devicemapper, Docker may be confused about which one to use.

The error message will often tell you which drivers were detected:
- "contains several valid graphdrivers: aufs, overlay2"
- "contains several valid graphdrivers: devicemapper, overlay2"

Explicitly set the storage driver to overlay2 (recommended for most systems):

sudo mkdir -p /etc/docker
sudo tee /etc/docker/daemon.json <<EOF
{
  "storage-driver": "overlay2"
}
EOF

# Restart Docker
sudo systemctl restart docker

Note: If you're on an older system without overlay2 support, you may need to use a different driver. Check Docker's storage driver documentation for compatibility.

Warning: This will delete all containers, images, and volumes. Back up important data first!

If you need to switch storage drivers and clean up old data:

# Stop Docker
sudo systemctl stop docker

# Remove the old storage driver directory (e.g., aufs)
sudo rm -rf /var/lib/docker/aufs

# Or if switching from devicemapper
sudo rm -rf /var/lib/docker/devicemapper

# Start Docker with the new driver
sudo systemctl start docker

Alternatively, to completely reset Docker:

sudo rm -rf /var/lib/docker/*
sudo systemctl start docker

If you're using Docker Desktop and see this error, perform a factory reset:

1. Open Docker Desktop
2. Go to Settings (gear icon)
3. Navigate to Troubleshoot
4. Click Reset to factory defaults

This will clear all Docker data and reset the storage driver configuration.

Alternatively, from the error dialog, you may see a "reset docker to factory defaults" button - click it to resolve the conflict.

After applying fixes, verify Docker is functioning correctly:

# Check Docker daemon status
sudo systemctl status docker

# Verify the storage driver in use
docker info | grep "Storage Driver"

# Run a test container
docker run --rm hello-world

The storage driver should now show "overlay2" (or your configured driver), and the test container should run successfully.