How to fix [ERROR CRI]: container runtime is not running in Kubernetes

# Check for containerd:
which containerd
containerd --version

# Check for Docker:
which docker
docker --version

# Check for CRI-O:
which crio
crio --version

# For containerd:
sudo systemctl start containerd
sudo systemctl enable containerd

# For Docker:
sudo systemctl start docker
sudo systemctl enable docker

# For CRI-O:
sudo systemctl start crio
sudo systemctl enable crio

# Verify it's running:
sudo systemctl status containerd

# Check the config:
sudo cat /etc/containerd/config.toml | grep disabled_plugins

# If you see disabled_plugins = ["cri"], edit it:
sudo nano /etc/containerd/config.toml

# Comment out or remove the line:
# disabled_plugins = ["cri"]

# Or delete and regenerate the config:
sudo rm /etc/containerd/config.toml
sudo mkdir -p /etc/containerd
sudo containerd config default | sudo tee /etc/containerd/config.toml

# Restart containerd:
sudo systemctl restart containerd

# Check kubelet configuration:
sudo cat /etc/kubernetes/kubelet.conf | grep container-runtime

# Typical runtime socket paths:
# - containerd: unix:///run/containerd/containerd.sock
# - Docker: unix:///var/run/docker.sock
# - CRI-O: unix:///var/run/crio/crio.sock

# If needed, edit kubelet service:
sudo systemctl edit kubelet

# Add or update the flag (if not already set):
# Environment="KUBELET_EXTRA_ARGS=--container-runtime=remote --container-runtime-endpoint=unix:///run/containerd/containerd.sock"

# Restart kubelet:
sudo systemctl daemon-reload
sudo systemctl restart kubelet

# For containerd:
ls -la /run/containerd/containerd.sock

# For Docker:
ls -la /var/run/docker.sock

# For CRI-O:
ls -la /var/run/crio/crio.sock

# Test connection:
sudo ctr version     # for containerd
docker ps            # for Docker

# View kubelet journal:
sudo journalctl -u kubelet -n 50 -f

# Or check kubelet logs:
sudo cat /var/log/kubelet.log | tail -100

# Look for:
# - Connection refused
# - File not found
# - Permission denied
# - Version mismatch

# For containerd:
sudo apt-get remove containerd -y
sudo apt-get install containerd -y
sudo mkdir -p /etc/containerd
sudo containerd config default | sudo tee /etc/containerd/config.toml
sudo systemctl restart containerd

# For Docker:
sudo apt-get remove docker.io docker-ce -y
sudo apt-get install docker.io -y
sudo systemctl start docker

# Verify:
sudo systemctl status containerd

# For worker nodes:
kubeadm reset  # Only if the node was corrupted
kubeadm join <master-ip>:6443 --token <token> --discovery-token-ca-cert-hash sha256:<hash>

# For control plane nodes (if node isn't working):
sudo systemctl restart kubelet

# Check node status:
kubectl get nodes -o wide
kubectl describe node <node-name>