dumping groups and users

Hi,

I wrote an external C program for using users and groups (calling psql
externally), so I use groups and users agressively. For backing these data
up and copy the entire database (with groups and users) to a different
Linux server I usually stop both databases (i.e. postmaster), copy all the
pg_* files from the data/ directory from the old to the new server, and
start the databases (i.e. postmaster) again. (Is this right?)

OK, the problem is with different Linux systems where the user accounts
may differ (e.g. the postgres user's id, too; for example Red Hat and
SuSE). OK, I can write an internal function to do this conversion. Is
there a better idea for doing this? What are your ways instead of mine?
Is a TODO item for writing a tool for dumping groups and users?

Thanks in advice, regards,
Zoltan