Error while setting up platform rpi_gpio ... using HASSIO in docker

I installed HASSIO on an existing pi3 (hence in a docker container), now I need my HASSIO installation to interact with GPIO, but I have this error…
I added to the group GPIO the user hass, my user in HASSIO, the user for which I connect to the pi3 … but is not working … any advice?

2019-02-09 13:10:21 ERROR (MainThread) [homeassistant.components.switch] Error while setting up platform rpi_gpio
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/homeassistant/helpers/entity_platform.py", line 128, in _async_setup_platform
    SLOW_SETUP_MAX_WAIT, loop=hass.loop)
  File "/usr/local/lib/python3.6/asyncio/tasks.py", line 358, in wait_for
    return fut.result()
  File "/usr/local/lib/python3.6/concurrent/futures/thread.py", line 56, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/usr/local/lib/python3.6/site-packages/homeassistant/components/switch/rpi_gpio.py", line 44, in setup_platform
    switches.append(RPiGPIOSwitch(name, port, invert_logic))
  File "/usr/local/lib/python3.6/site-packages/homeassistant/components/switch/rpi_gpio.py", line 57, in __init__
    rpi_gpio.setup_output(self._port)
  File "/usr/local/lib/python3.6/site-packages/homeassistant/components/rpi_gpio.py", line 39, in setup_output
    GPIO.setup(port, GPIO.OUT)
RuntimeError: No access to /dev/mem.  Try running as root!

Annyone > I have the same problem :frowning: