The binary installation of Kubernetes 1.18 is in the order of：etcd->apiserver->kubctl，When using kubectl, the cluster information and user information are configured as follows:

[root@master-01 ~]# ll ~/.kube/config
-rw------- 1 root root 6257 Apr 20 22:49 /root/.kube/config
[root@master-01 ~]#

However, an error is still reported when using kubctl：

[root@master-01 ~]# kubectl get ns
error: no configuration has been provided, try setting KUBERNETES_MASTER environment variable
[root@master-01 ~]#

Ask which can help look, thank you!