How to fix port 6443 is in use in Kubernetes

sudo netstat -tulpn | grep 6443
# or
sudo lsof -Pi :6443

sudo kubeadm reset -f
sudo rm -rf /etc/kubernetes /var/lib/kubernetes /var/lib/kubelet /etc/cni/net.d ~/.kube
sudo docker rm -f $(docker ps -a -q)  # Remove all containers
sudo iptables -F && sudo iptables -X  # Flush firewall rules

# From netstat/lsof output, get the PID and kill it:
sudo kill -9 <PID>

# Or force kill all docker containers:
sudo docker rm -f $(docker ps -a -q)

sudo netstat -tulpn | grep 6443
# Should show nothing

sudo systemctl status docker
# or
sudo systemctl status containerd

sudo systemctl start docker

sudo docker ps
sudo ctr containers list  # For containerd

# HAproxy should forward to API servers, not bind to 6443:
listen api-server
  bind <load-balancer-ip>:443  # NOT 6443
  default_backend api-servers

backend api-servers
  server master1 <master1-ip>:6443 check
  server master2 <master2-ip>:6443 check
  server master3 <master3-ip>:6443 check

kubeadm init --control-plane-endpoint=<load-balancer-ip>:443

sudo kubeadm init \
  --pod-network-cidr=10.244.0.0/16 \
  --control-plane-endpoint=<control-plane-ip>:6443

sudo docker ps -a  # Should be empty
sudo systemctl status etcd  # Should not be running

# Monitor startup:
kubectl get nodes -w

# Or check logs:
sudo journalctl -u kubelet -f
sudo docker logs -f <api-server-container>

# Check if installed:
which cri-dockerd

# Install if missing:
wget https://github.com/Mirantis/cri-dockerd/releases/download/v0.2.6/cri-dockerd-0.2.6.amd64.tgz
tar -xzf cri-dockerd-0.2.6.amd64.tgz
sudo mv cri-dockerd/cri-dockerd /usr/local/bin/

# Then run kubeadm:
kubeadm init --cri-socket /run/cri-dockerd.sock

sudo kubeadm init phase preflight