title: kubeadm fails to initialize when kubeadm init is called
body: <p>I am new to kubernetes and trying to configure kubernetes master node, I have installed kubeadm, kubectl and kubelet following </p>
  
  <p><a href="https://kubernetes.io/docs/setup/independent/create-cluster-kubeadm/" rel="noreferrer">https://kubernetes.io/docs/setup/independent/create-cluster-kubeadm/</a></p>
  
  <p>but when I try to start kubeadm by typing <code>kubeadm init</code>, it gives me the following error</p>
  
  <pre><code>[init] Using Kubernetes version: v1.14.0
  [preflight] Running pre-flight checks
          [WARNING Firewalld]: no supported init system detected, skipping checking for services
          [WARNING Service-Docker]: no supported init system detected, skipping checking for services
          [WARNING IsDockerSystemdCheck]: detected "cgroupfs" as the Docker cgroup driver. The recommended driver is "systemd". Please follow the guide at https://kubernetes.io/docs/setup/cri/
          [WARNING Service-Kubelet]: no supported init system detected, skipping checking for services
  error execution phase preflight: [preflight] Some fatal errors occurred:
          [ERROR FileAvailable--etc-kubernetes-manifests-kube-apiserver.yaml]: /etc/kubernetes/manifests/kube-apiserver.yaml already exists
          [ERROR FileAvailable--etc-kubernetes-manifests-kube-controller-manager.yaml]: /etc/kubernetes/manifests/kube-controller-manager.yaml already exists
          [ERROR FileAvailable--etc-kubernetes-manifests-kube-scheduler.yaml]: /etc/kubernetes/manifests/kube-scheduler.yaml already exists
          [ERROR FileAvailable--etc-kubernetes-manifests-etcd.yaml]: /etc/kubernetes/manifests/etcd.yaml already exists
          [ERROR FileContent--proc-sys-net-ipv4-ip_forward]: /proc/sys/net/ipv4/ip_forward contents are not set to 1
  [preflight] If you know what you are doing, you can make a check non-fatal with `--ignore-preflight-errors=...`
  </code></pre>