The -n flag

kubectl commands run by default in the active context's namespace (usually default). For another namespace, -n (--namespace) is added to each command:

kubectl get pods -n dev
kubectl apply -f web.yaml -n dev        # if the YAML has no namespace
kubectl logs deploy/web -n prod
kubectl exec -it -n prod deploy/web -- sh

If metadata.namespace is written in the YAML and -n differs, kubectl errors.

-n can be written anywhere in the command; but in exec and run commands it must come before --, otherwise it counts as an argument of the command in the container:

kubectl -n prod get pods              # right
kubectl get pods -n prod              # right
kubectl exec deploy/web -n prod -- ls # right
kubectl exec deploy/web -- ls -n prod # wrong: -n goes to ls