install failure if user postgres already exists and group postgres is missing

For some useful information:
I am using NIS services for sharing account information. When postinstallation script of postgresql-common is running the following command

"if ! getent passwd postgres > /dev/null"

its giving the wrong information. So the following command is not executing properly

 adduser --system --quiet --home /var/lib/postgresql --no-create-home \
            --shell /bin/bash --group --gecos "PostgreSQL administrator" postgres

I already had user postgres in the shadowpassword. So the following command is giving the user id which is right

~# id -u postgres
1004

but postgres user is not assign to group postgres. Besically there was no group called postgres. So when postgresql-common installation script is checking for group id its getting wrong value. The following command is not getting the right value

~# id -g postgres
100

These commands are besically giving a totaly wrong output to the postgresql-common installation.
if [ "`id -g postgres`" -eq 0 ]; then
        echo "The postgres system user must not have root as primary group.
Please fix this and reinstall this package." >&2
        exit 1
    fi

Because of that the following command is not executing

` chown postgres:postgres /var/lib/postgresql`

and giving an error exit status 1 and which stopping the script to execute. As a result the whole installation is breaking down.

My other packages are depend on postgresql-8.2 package. So if it does not installed all other breakdown. So I hope you will do something about it. Possible add something to the script to overcome this situation. I will be very grateful to you if you solve this problem. Thanks

Thanks for taking time reporting this bug.
I set the importance for this bug to Medium because there is a workaround (see answer #17811 - https://answers.launchpad.net/ubuntu/+question/17811).

So, did I understand this correctly? User postgres already existed, but group postgres didn't? adduser will not create the group only in this case.

I could create the group separately, but usually this situation means that you have a half-broken installation already. If you use NIS authentication, then you should have both users and groups in nis, not just users. Will 'addgroup postgresql' create the group in NIS for you or just locally?

If the groups does not exits in nis or in any where, I think it should create the groups in locally.

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.