Docker Daemon Not Starting on Linux — Fix Guide

# Check if Docker service is running
sudo systemctl status docker
 
# If stopped/failed, check why
sudo journalctl -u docker.service -n 50 --no-pager
 
# Try to start it manually
sudo systemctl start docker
 
# Check if it stays up
sudo systemctl status docker
sleep 3
sudo systemctl status docker

# Check if the file exists and is valid
cat /etc/docker/daemon.json
python3 -m json.tool /etc/docker/daemon.json
 
# If malformed JSON, you'll see: JSONDecodeError

{
  "storage-driver": "overlay2",
  "insecure-registries": ["192.168.1.10:5000",]  // Trailing comma — invalid JSON!
}

# Validate and fix
cat /etc/docker/daemon.json | python3 -c "import sys,json; json.load(sys.stdin); print('Valid JSON')"
 
# Or just reset to defaults
sudo mv /etc/docker/daemon.json /etc/docker/daemon.json.bak
sudo systemctl start docker

# Check journal for storage driver errors
sudo journalctl -u docker.service | grep -i "storage\|overlay\|devicemapper"
 
# Common error:
# "Error starting daemon: error initializing graphdriver: driver not supported"
# "overlay2: filesystem not supported on this kernel"

# Check what storage drivers are available
ls /proc/filesystems | grep overlay
 
# If overlay2 not in kernel modules, load it
sudo modprobe overlay
 
# Make permanent
echo "overlay" | sudo tee -a /etc/modules-load.d/docker.conf
 
# Check kernel version (overlay2 needs 4.0+)
uname -r

// /etc/docker/daemon.json
{
  "storage-driver": "vfs"   // Fallback (slower but always works)
}

# Check for corruption errors in logs
sudo journalctl -u docker.service | grep -i "corrupt\|error\|failed"
 
# If metadata is corrupted, a clean restart may fix it
sudo systemctl stop docker
sudo rm -rf /var/lib/docker/tmp
sudo systemctl start docker

sudo systemctl stop docker
sudo rm -rf /var/lib/docker
sudo systemctl start docker
 
# After this, Docker starts fresh — no images or containers

# Check if docker socket or port is already in use
sudo fuser /var/run/docker.sock
ls -la /var/run/docker.sock
 
# Remove stale socket
sudo rm /var/run/docker.sock
sudo systemctl start docker

# Check disk space
df -h /var/lib/docker
df -h /
 
# If full, clean up Docker objects
sudo docker system prune -a --volumes   # WARNING: removes all unused data
 
# Or just dangling images
sudo docker image prune
 
# Show what's taking space
sudo docker system df

# Check cgroup version
stat -fc %T /sys/fs/cgroup/
 
# If output is "cgroup2fs" (cgroup v2), some older Docker configs break
# Check Docker logs for cgroup errors
sudo journalctl -u docker.service | grep cgroup

// /etc/docker/daemon.json
{
  "exec-opts": ["native.cgroupdriver=systemd"],
  "log-driver": "json-file",
  "log-opts": {
    "max-size": "100m"
  },
  "storage-driver": "overlay2"
}

# Check if SELinux is blocking
sudo ausearch -m avc -ts recent | grep docker
 
# Temporary fix (not for production)
sudo setenforce 0
sudo systemctl start docker
 
# Proper fix — set SELinux to permissive for docker
sudo setsebool -P container_manage_cgroup on

sudo aa-status | grep docker
sudo apparmor_parser -R /etc/apparmor.d/docker 2>/dev/null
sudo systemctl start docker

#!/bin/bash
echo "=== Docker Daemon Diagnosis ==="
 
echo -e "\n--- Service Status ---"
sudo systemctl status docker --no-pager
 
echo -e "\n--- Recent Logs ---"
sudo journalctl -u docker.service -n 20 --no-pager
 
echo -e "\n--- Disk Space ---"
df -h /var/lib/docker /
 
echo -e "\n--- daemon.json ---"
cat /etc/docker/daemon.json 2>/dev/null || echo "No daemon.json found"
 
echo -e "\n--- Storage Driver Modules ---"
lsmod | grep -E "overlay|dm_|btrfs"
 
echo -e "\n--- Docker Socket ---"
ls -la /var/run/docker.sock 2>/dev/null || echo "Socket not found"
 
echo -e "\n--- Kernel Version ---"
uname -r

# Verify Docker is working
docker info
docker run --rm hello-world
 
# Enable Docker to start on boot
sudo systemctl enable docker