Giovanni,
Unfortunately, I'm not sure how your "service" command works. Is
anybody else familiar with this from Red Hat?
The command that you need to be passing to your back-end is:
su -c "<postgres dir>/bin/pg_ctl -o '-i' -l <log file location> -D
<postgres dir>/data" postgres
... where <postgres dir> and <log file location> are replaced with the
actual locations for those files/directories on your system.
-Josh Berkus