Since as you reported, "id -g postgres" already gives "100", testing for the group would succeed, and thus even explicitly creating the group wouldn't be done. I think you should just fix your NIS setup to be consistent. Working around those problems will only aggravate the problem by creating a wild mix of local and NIS groups amongst machines, leading to broken file permissions.
Since as you reported, "id -g postgres" already gives "100", testing for the group would succeed, and thus even explicitly creating the group wouldn't be done. I think you should just fix your NIS setup to be consistent. Working around those problems will only aggravate the problem by creating a wild mix of local and NIS groups amongst machines, leading to broken file permissions.