As with any program, you might run into an error installing or running kubeadm. This page lists some common failure scenarios and have provided steps that can help you understand and fix the problem.
If your problem is not listed below, please follow the following steps:
If you think your problem is a bug with kubeadm:
If you see the following warnings while running
[preflight] WARNING: ebtables not found in system path [preflight] WARNING: ethtool not found in system path
Then you may be missing
ethtool or a similar executable on your node. You can install them with the following commands:
apt install ebtables ethtool.
yum install ebtables ethtool.
If you notice that
kubeadm init hangs after printing out the following line:
[apiclient] Created API client, waiting for the control plane to become ready
This may be caused by a number of problems. The most common are:
the default cgroup driver configuration for the kubelet differs from that used by Docker.
Check the system log file (e.g.
/var/log/message) or examine the output from
journalctl -u kubelet. If you see something like the following:
error: failed to run Kubelet: failed to create kubelet: misconfiguration: kubelet cgroup driver: "systemd" is different from docker cgroup driver: "cgroupfs"
There are two common ways to fix the cgroup driver problem:
docker psand investigating each container by running
The following could happen if Docker halts and does not remove any Kubernetes-managed containers:
sudo kubeadm reset [preflight] Running pre-flight checks [reset] Stopping the kubelet service [reset] Unmounting mounted directories in "/var/lib/kubelet" [reset] Removing kubernetes-managed containers (block)
A possible solution is to restart the Docker service and then re-run
sudo systemctl restart docker.service sudo kubeadm reset
Inspecting the logs for docker may also be useful:
journalctl -ul docker
kubeadm init there should not be any pods in these states.
kubeadm init, please open an issue in the kubeadm repo.
kube-dns) should be in the
Pendingstate until you have deployed the network solution.
Errorstate after deploying the network solution and nothing happens to
kube-dns), it’s very likely that the Pod Network solution that you installed is somehow broken. You might have to grant it more RBAC privileges or use a newer version. Please file an issue in the Pod Network providers’ issue tracker and get the issue triaged there.
MountFlags=slaveoption when booting
docker. You can see the MountFlags in
/usr/lib/systemd/system/docker.service. MountFlags can interfere with volumes mounted by Kubernetes, and put the Pods in
CrashLoopBackOffstate. The error happens when Kubernetes does not find
This is expected and part of the design. kubeadm is network provider-agnostic, so the admin
should install the pod network solution
of choice. You have to install a Pod Network
before CoreDNS may deployed fully. Hence the
Pending state before the network is set up.
HostIP functionality is available depending on your Pod Network
provider. Please contact the author of the Pod Network solution to find out whether
HostIP functionality are available.
Calico, Canal, and Flannel CNI providers are verified to support HostPort.
For more information, see the CNI portmap documentation.
If your network provider does not support the portmap CNI plugin, you may need to use the NodePort feature of
services or use
Many network add-ons do not yet enable hairpin mode which allows pods to access themselves via their Service IP. This is an issue related to CNI. Please contact the network add-on provider to get the latest status of their support for hairpin mode.
If you are using VirtualBox (directly or via Vagrant), you will need to
hostname -i returns a routable IP address. By default the first
interface is connected to a non-routable host-only network. A work around
is to modify
/etc/hosts, see this Vagrantfile
for an example.
The following error indicates a possible certificate mismatch.
# kubectl get pods Unable to connect to the server: x509: certificate signed by unknown authority (possibly because of "crypto/rsa: verification error" while trying to verify candidate authority certificate "kubernetes")
$HOME/.kube/configfile contains a valid certificate, and regenerate a certificate if necessary. The certificates in a kubeconfig file are base64 encoded. The
base64 -dcommand can be used to decode the certificate and
openssl x509 -text -nooutcan be used for viewing the certificate information.
KUBECONFIG environment variable using:
Or set it to the default
Another workaround is to overwrite the existing
kubeconfig for the “admin” user:
mv $HOME/.kube $HOME/.kube.bak sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config sudo chown $(id -u):$(id -g) $HOME/.kube/config
The following error might indicate that something was wrong in the pod network:
Error from server (NotFound): the server could not find the requested resource
Vagrant typically assigns two interfaces to all VMs. The first, for which all hosts are assigned the IP address
10.0.2.15, is for external traffic that gets NATed.
This may lead to problems with flannel, which defaults to the first interface on a host. This leads to all hosts thinking they have the same public IP address. To prevent this, pass the
--iface eth1 flag to flannel so that the second interface is chosen.
In some situations
kubectl logs and
kubectl run commands may return with the following errors in an otherwise functional cluster:
Error from server: Get https://10.19.0.41:10250/containerLogs/default/mysql-ddc65b868-glc5m/mysql: dial tcp 10.19.0.41:10250: getsockopt: no route to host
eth0as well as a private one to be used internally as anchor for their floating IP feature, yet
kubeletwill pick the latter as the node’s
InternalIPinstead of the public one.
ip addr show to check for this scenario instead of
ifconfig will not display the offending alias IP address. Alternatively an API endpoint specific to Digital Ocean allows to query for the anchor IP from the droplet:
The workaround is to tell
kubelet which IP to use using
--node-ip. When using Digital Ocean, it can be the public one (assigned to
eth0) or the private one (assigned to
eth1) should you want to use the optional private network. The
KubeletExtraArgs section of the kubeadm
NodeRegistrationOptions structure can be used for this.
systemctl daemon-reload systemctl restart kubelet
If you have nodes that are running SELinux with an older version of Docker you might experience a scenario
coredns pods are not starting. To solve that you can try one of the following options:
coredns deployment to set
kubectl -n kube-system get deployment coredns -o yaml | \ sed 's/allowPrivilegeEscalation: false/allowPrivilegeEscalation: true/g' | \ kubectl apply -f -
Another cause for CoreDNS to have
CrashLoopBackOff is when a CoreDNS Pod deployed in Kubernetes detects a loop. A number of workarounds
are available to avoid Kubernetes trying to restart the CoreDNS Pod every time CoreDNS detects the loop and exits.
警告: Disabling SELinux or setting
truecan compromise the security of your cluster.
If you encounter the following error:
rpc error: code = 2 desc = oci runtime error: exec failed: container_linux.go:247: starting container process caused "process_linux.go:110: decoding init error from pipe caused \"read parent: connection reset by peer\""
this issue appears if you run CentOS 7 with Docker 22.214.171.124. This version of Docker can prevent the kubelet from executing into the etcd container.
To work around the issue, choose one of these options:
Roll back to an earlier version of Docker, such as 1.13.1-75
yum downgrade docker-1.13.1-75.git8633870.el7.centos.x86_64 docker-client-1.13.1-75.git8633870.el7.centos.x86_64 docker-common-1.13.1-75.git8633870.el7.centos.x86_64
Install one of the more recent recommended versions, such as 18.06:
sudo yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo yum install docker-ce-18.06.1.ce-3.el7.x86_64
Thanks for the feedback. If you have a specific, answerable question about how to use Kubernetes, ask it on Stack Overflow. Open an issue in the GitHub repo if you want to report a problem or suggest an improvement.