Problem with volume mount from OSX

[StefanScherer]

First thank you very much for that Docker image. I have joined an editorial team in school and they use Scribus. So I thought using this inside a Docker container simplifies the installation on my Mac.

I use the following docker-compose.yml instead of using a long command line.

scribus:
  image: johnodon/scribus
  volumes:
    - .:/nobody
  ports:
    - 3389:3389
  environment:
    - USER_ID=501
    - GROUP_ID=20

On OSX the group is 20 = staff. In the Linux conainer group 20 already exists as dialout.

But spinning it up fails due to the chown in /etc/my_init.d/01_user_config.sh.

$ docker-compose up
Recreating jahresheft_scribus_1
Attaching to jahresheft_scribus_1
scribus_1 | *** Running /etc/my_init.d/00_config.sh...
scribus_1 | 
scribus_1 | Current default time zone: 'Etc/UTC'
scribus_1 | Local time is now:      Sat Mar  5 22:14:25 UTC 2016.
scribus_1 | Universal Time is now:  Sat Mar  5 22:14:25 UTC 2016.
scribus_1 | 
scribus_1 | *** Running /etc/my_init.d/01_user_config.sh...
scribus_1 | groupmod: GID '20' already exists
scribus_1 | usermod: no changes
scribus_1 | chown: changing ownership of ‘/nobody/Designtest_J1.sla’: Operation not permitted
scribus_1 | chown: changing ownership of ‘/nobody/Designtest_J2.sla’: Operation not permitted
scribus_1 | chown: changing ownership of ‘/nobody/docker-compose.yml’: Operation not permitted
scribus_1 | chown: changing ownership of ‘/nobody/’: Operation not permitted
scribus_1 | *** /etc/my_init.d/01_user_config.sh failed with status 1
scribus_1 | 
scribus_1 | *** Killing all processes...
jahresheft_scribus_1 exited with code 1

The problem seems to be the already existing group. I've done the steps manually in a container

docker run -v $(pwd):/nobody -e USER_ID=501 -e GROUP_ID=20 -it johnodon/scribus bash

and when I first remove the group groupdel dialout the rest of the script works fine.

Any ideas how this could be 'fixed' in the docker image?