<p>Just I am starting to learn Kubernetes. I've installed CentOS 7.5 with SELinux disabled kubectl, kubeadm and kubelet by Kubernetes YUM repository.</p>

<p>However, when I want to start a <code>kubeadm init</code> command. I get this error message:</p>

<pre><code>[init] using Kubernetes version: v1.12.2
[preflight] running pre-flight checks
    [WARNING Firewalld]: firewalld is active, please ensure ports [6443 10250] are open or your cluster may not function correctly
[preflight/images] Pulling images required for setting up a Kubernetes cluster
[preflight/images] This might take a minute or two, depending on the speed of your internet connection
[preflight/images] You can also perform this action in beforehand using 'kubeadm config images pull'
[kubelet] Writing kubelet environment file with flags to file "/var/lib/kubelet/kubeadm-flags.env"
[kubelet] Writing kubelet configuration to file "/var/lib/kubelet/config.yaml"
[preflight] Activating the kubelet service
[certificates] Generated front-proxy-ca certificate and key.
[certificates] Generated front-proxy-client certificate and key.
[certificates] Generated etcd/ca certificate and key.
[certificates] Generated etcd/peer certificate and key.
[certificates] etcd/peer serving cert is signed for DNS names [vps604805.ovh.net localhost] and IPs [51.75.201.75 127.0.0.1 ::1]
[certificates] Generated apiserver-etcd-client certificate and key.
[certificates] Generated etcd/server certificate and key.
[certificates] etcd/server serving cert is signed for DNS names [vps604805.ovh.net localhost] and IPs [127.0.0.1 ::1]
[certificates] Generated etcd/healthcheck-client certificate and key.
[certificates] Generated ca certificate and key.
[certificates] Generated apiserver certificate and key.
[certificates] apiserver serving cert is signed for DNS names [vps604805.ovh.net kubernetes kubernetes.default kubernetes.default.svc kubernetes.default.svc.cluster.local] and IPs [10.96.0.1 51.75.201.75]
[certificates] Generated apiserver-kubelet-client certificate and key.
[certificates] valid certificates and keys now exist in "/etc/kubernetes/pki"
[certificates] Generated sa key and public key.
[kubeconfig] Wrote KubeConfig file to disk: "/etc/kubernetes/admin.conf"
[kubeconfig] Wrote KubeConfig file to disk: "/etc/kubernetes/kubelet.conf"
[kubeconfig] Wrote KubeConfig file to disk: "/etc/kubernetes/controller-manager.conf"
[kubeconfig] Wrote KubeConfig file to disk: "/etc/kubernetes/scheduler.conf"
[controlplane] wrote Static Pod manifest for component kube-apiserver to "/etc/kubernetes/manifests/kube-apiserver.yaml"
[controlplane] wrote Static Pod manifest for component kube-controller-manager to "/etc/kubernetes/manifests/kube-controller-manager.yaml"
[controlplane] wrote Static Pod manifest for component kube-scheduler to "/etc/kubernetes/manifests/kube-scheduler.yaml"
[etcd] Wrote Static Pod manifest for a local etcd instance to "/etc/kubernetes/manifests/etcd.yaml"
[init] waiting for the kubelet to boot up the control plane as Static Pods from directory "/etc/kubernetes/manifests" 
[init] this might take a minute or longer if the control plane images have to be pulled
[apiclient] All control plane components are healthy after 26.003496 seconds
[uploadconfig] storing the configuration used in ConfigMap "kubeadm-config" in the "kube-system" Namespace
[kubelet] Creating a ConfigMap "kubelet-config-1.12" in namespace kube-system with the configuration for the kubelets in the cluster
[markmaster] Marking the node vps604805.ovh.net as master by adding the label "node-role.kubernetes.io/master=''"
[markmaster] Marking the node vps604805.ovh.net as master by adding the taints [node-role.kubernetes.io/master:NoSchedule]
error marking master: timed out waiting for the condition
</code></pre>

<p>According to Linux Foundation course, I don't need more command to execute to create my first start cluster into my VM.</p>

<p>Wrong?</p>

<p>Firewalld does have open ports into firewall. 6443/tcp and 10248-10252</p>

<p>I would recommend to bootstrap Kubernetes cluster as guided in the official <a href="https://kubernetes.io/docs/setup/independent/install-kubeadm/" rel="noreferrer">documentation</a>. I've proceeded with some steps to build cluster on the same CentOS version <code>CentOS Linux release 7.5.1804 (Core)</code> and will share them with you, hope it can be helpful to you to get rid of the issue during installation.</p>

<p>First wipe your current cluster installation:</p>

<pre><code># kubeadm reset -f &amp;&amp; rm -rf /etc/kubernetes/
</code></pre>

<p>Add Kubernetes repo for further <code>kubeadm</code>, <code>kubelet</code>, <code>kubectl</code> installation:</p>

<pre><code>[kubernetes]
name=Kubernetes
baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-x86_64
enabled=1
gpgcheck=1
repo_gpgcheck=1
gpgkey=https://packages.cloud.google.com/yum/doc/yum-key.gpg https://packages.cloud.google.com/yum/doc/rpm-package-key.gpg
exclude=kube*
EOF
</code></pre>

<p>Check whether <code>SELinux</code> is in permissive mode:</p>

<pre><code># getenforce
Permissive
</code></pre>

<p>Ensure <code>net.bridge.bridge-nf-call-iptables</code> is set to 1 in your sysctl:</p>

<pre><code># cat &lt;&lt;EOF &gt;  /etc/sysctl.d/k8s.conf
net.bridge.bridge-nf-call-ip6tables = 1
net.bridge.bridge-nf-call-iptables = 1
EOF
sysctl --system
</code></pre>

<p>Install required Kubernetes components and start services:</p>

<pre><code># yum update &amp;&amp; yum upgrade &amp;&amp; yum install -y docker kubelet kubeadm kubectl --disableexcludes=kubernetes

# systemctl start docker kubelet &amp;&amp; systemctl enable docker kubelet
</code></pre>

<p>Deploy the cluster via <code>kubeadm</code>:</p>

<pre><code>kubeadm init --pod-network-cidr=10.244.0.0/16
</code></pre>

<p>I prefer to install <code>Flannel</code> as the main <code>CNI</code> in my cluster, although there are some prerequisites for proper <a href="https://kubernetes.io/docs/setup/independent/create-cluster-kubeadm/#pod-network" rel="noreferrer">Pod network</a> installation, I've passed <code>--pod-network-cidr=10.244.0.0/16</code> flag to <code>kubeadm init</code> command.</p>

<p>Create Kubernetes Home directory for your user and store <code>config</code> file:</p>

<pre><code>$ mkdir -p $HOME/.kube
$ sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
$ sudo chown $(id -u):$(id -g) $HOME/.kube/config
</code></pre>

<p>Install Pod network, in my case it was <code>Flannel</code>:</p>

<p><code>$ kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/bc79dd1505b0c8681ece4de4c0d86c5cd2643275/Documentation/kube-flannel.yml</code></p>

<p>Finally check Kubernetes core Pods status:</p>

<p><code>$ kubectl get pods --all-namespaces</code></p>

<pre><code>NAMESPACE     NAME                                 READY   STATUS    RESTARTS   AGE
kube-system   coredns-576cbf47c7-4x7zq             1/1     Running   0          36m
kube-system   coredns-576cbf47c7-666jm             1/1     Running   0          36m
kube-system   etcd-centos-7-5                      1/1     Running   0          35m
kube-system   kube-apiserver-centos-7-5            1/1     Running   0          35m
kube-system   kube-controller-manager-centos-7-5   1/1     Running   0          35m
kube-system   kube-flannel-ds-amd64-2bmw9          1/1     Running   0          33m
kube-system   kube-proxy-pcgw8                     1/1     Running   0          36m
kube-system   kube-scheduler-centos-7-5            1/1     Running   0          35m
</code></pre>

<p>In case you still have any doubts, just write down a comment below this answer.</p>
