I have a gitlab server that can be started up with a docker-compose.yml file.

The gitlab server runs on a Macbook Pro computer.

There are 3 volumes inside the docker-compose.yml file.

volumes:
   - './config:/etc/gitlab'
   - './logs:/var/log/gitlab'
   - './data:/var/opt/gitlab'

Today I want to try if the volumes can be changed to an NFS of a Synology NAS.

So I type the following commands to create a mount point.

sudo mkdir /Volumes/my-backup
sudo mount -t nfs -o resvport,rw nas.mydomain:/volume1/my-backup /Volumes/my-backup

Then I change the volumes section of docker-compose.yml file to this:

volumes:
  - '/Volumes/my-backup/gitlab-mount-volume/config:/etc/gitlab'
  - '/Volumes/my-backup/gitlab-mount-volume/logs:/var/log/gitlab'
  - '/Volumes/my-backup/gitlab-mount-volume/data:/var/opt/gitlab'

/Volumes/my-backup/gitlab-mount-volume/data/ folder contains the files that are created with cp -a ./data/* /Volumes/my-backup/gitlab-mount-volume/data/ command.

-a option can preserve the owner, group, and permissions of all the copied files.

Then I see the following error messages after running docker compose up command

gitlab-service-web-1  | ---- Begin output of chgrp git /var/opt/gitlab/git-data/repositories ----
gitlab-service-web-1  | STDOUT:
gitlab-service-web-1  | STDERR: chgrp: changing group of '/var/opt/gitlab/git-data/repositories': Operation not permitted
gitlab-service-web-1  | ---- End output of chgrp git /var/opt/gitlab/git-data/repositories ----
gitlab-service-web-1  | Ran chgrp git /var/opt/gitlab/git-data/repositories returned 1

Why does chgrp command generates an Operation not permitted error inside the docker container?

I've run cat /etc/export command to check that the mount point contains no_root_squash option.

192.168.123.123(rw,async,no_wdelay,crossmnt,insecure,no_root_squash,insecure_locks,sec=sys,anonuid=1025,anongid=100)