How to fix cgroups: cgroup mountpoint does not exist: unknown in Docker

# Check if cgroup v2 is in use
if [ -f /sys/fs/cgroup/cgroup.controllers ]; then
    echo "cgroup v2 (unified hierarchy) is active"
else
    echo "cgroup v1 (legacy hierarchy) is active"
fi

# Alternative: check mount type
mount | grep cgroup

docker version

# Ubuntu/Debian
curl -fsSL https://get.docker.com | sh

# Or use package manager with Docker's official repo

# Remove old Docker packages
sudo apt-get remove docker docker-engine docker.io containerd runc

# Install prerequisites
sudo apt-get update
sudo apt-get install ca-certificates curl gnupg

# Add Docker's official GPG key
sudo install -m 0755 -d /etc/apt/keyrings
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg
sudo chmod a+r /etc/apt/keyrings/docker.gpg

# Add the repository
echo \
  "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu \
  $(. /etc/os-release && echo "$VERSION_CODENAME") stable" | \
  sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

# Install Docker
sudo apt-get update
sudo apt-get install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

# Verify installation
docker version

# Edit GRUB configuration
sudo nano /etc/default/grub

# Add to GRUB_CMDLINE_LINUX:
GRUB_CMDLINE_LINUX="systemd.unified_cgroup_hierarchy=0"

# Update GRUB
sudo update-grub

# Reboot
sudo reboot

sudo dnf install grubby
sudo grubby --update-kernel=ALL --args="systemd.unified_cgroup_hierarchy=0"
sudo reboot

# Mount the cgroup filesystem
sudo mkdir -p /sys/fs/cgroup
sudo mount -t tmpfs cgroup_root /sys/fs/cgroup

# Mount systemd cgroup (often required)
sudo mkdir -p /sys/fs/cgroup/systemd
sudo mount -t cgroup -o none,name=systemd cgroup /sys/fs/cgroup/systemd

# For cgroup v1, mount individual controllers
for controller in cpu cpuacct cpuset memory devices freezer net_cls blkio; do
    sudo mkdir -p /sys/fs/cgroup/$controller
    sudo mount -t cgroup -o $controller cgroup /sys/fs/cgroup/$controller
done

docker-machine ssh default "sudo mkdir -p /sys/fs/cgroup/systemd"
docker-machine ssh default "sudo mount -t cgroup -o none,name=systemd cgroup /sys/fs/cgroup/systemd"

# Create or edit daemon.json
sudo mkdir -p /etc/docker
sudo tee /etc/docker/daemon.json <<EOF
{
  "exec-opts": ["native.cgroupdriver=systemd"],
  "default-cgroupns-mode": "host"
}
EOF

# Restart Docker
sudo systemctl restart docker

services:
  - docker:20.10.16-dind  # Use 20.10+ instead of 19.03

variables:
  DOCKER_HOST: tcp://docker:2376
  DOCKER_TLS_CERTDIR: "/certs"

volumes:
  - name: cgroup
    hostPath:
      path: /sys/fs/cgroup
      type: Directory
volumeMounts:
  - name: cgroup
    mountPath: /sys/fs/cgroup
    readOnly: true

# Check if memory cgroup is enabled
cat /proc/cgroups | grep memory

# If disabled, edit GRUB configuration
sudo nano /etc/default/grub

# Add memory controller options:
GRUB_CMDLINE_LINUX="cgroup_enable=memory swapaccount=1"

# Update GRUB and reboot
sudo update-grub
sudo reboot

cat /proc/cgroups | grep memory
# Should show: memory  X  X  1 (where 1 means enabled)

# Check Docker daemon status
sudo systemctl status docker

# Verify cgroup driver configuration
docker info | grep -i cgroup

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

# Check container resource constraints work
docker run --rm --memory=100m alpine cat /sys/fs/cgroup/memory.max 2>/dev/null || \
docker run --rm --memory=100m alpine cat /sys/fs/cgroup/memory/memory.limit_in_bytes