You want the directory to be setgid, so,
chmod 2777 .
This create any file in that directory to be created with the same groups perms. as the directory.
Is that sufficient?
Almost, except if one user creates a file, the second user can't modify it; although the second user can delete the file, which I think is odd. Example; -rwxrwsrwx 1 herman users 0 Oct 21 09:58 test-1.txt -rwxrwsrwx 1 herman users 0 Oct 21 09:57 test-2.txt -rwxrwsrwx 1 herman users 0 Oct 21 09:56 test-3.txt -rw-r--r-- 1 postgres users 0 Oct 21 11:43 new-file.txt -rw-r--r-- 1 herman users 0 Oct 21 11:46 herman-file.txt -rwxrwsrwx 1 postgres users 679 Oct 21 10:38 source_system.txt -rwxrwsrwx 1 herman users 0 Oct 21 09:54 test-postgres.txt #chmod -R 2777 dir-in-question #cd dir-in-question user 'herman' creates file herman-file.txt user 'postgres' can't modify the file, however user postgres can 'rm' file herman-file.txt. Any ideas? Thank you. ~James