docker-baseimage-ubuntu/root/usr/bin/with-contenv

#! /bin/bash
if [[ -f /var/run/s6/container_environment/UMASK ]] && [[ "$(pwdx $$)" =~ "/run/s6/services/" ]]; then
  umask $(cat /var/run/s6/container_environment/UMASK)
  exec /command/with-contenv "$@"
else
  exec /command/with-contenv "$@"
fi