#!/bin/bash
kubectl get pods \
  -l app=mubu7 \
  -o jsonpath='{range .items[*]}{.metadata.name} \
  {.spec.containers[*].name}{"\n"}{end}' | \
  while read pod containers; do 
     containers=($containers);
     for container in ${containers[@]};do
         kubectl exec -i ${pod} -c "$container" </dev/null \
         -- service ssh start
     done
  done

# answer to my question 
# https://stackoverflow.com/questions/70908483/kubectl-execute-command-in-all-containers-of-multiple-multi-container-pods
# docs at https://kubernetes.io/docs/reference/kubectl/jsonpath/ suggest 
# {"\t"} between between the 2 following
# items {.metadata.name} {.spec.containers[*].name}
# but space works fine