Postgresql on Ubuntu 10.4 doesn’t start on boot

I'm trying to have postgresql 8.4 start on boot on Ubuntu server 10.04 (64bit).

First, I tried putting: su -c 'pg_ctl start -D /home/postgres -l /home/postgres/serverlog' --preserve-environment postgres
at the end of init.d/rc.local, to no avail. The serverlog file wasn't even on the system.

Then I tried to run update-rc.d postgresql-8.4 defaults, which spewed out:

System start/stop links for /etc/init.d/postgresql-8.4 already exist.

A relevant piece of info is that by running su -c 'pg_ctl start -D /home/postgres -l /home/postgres/serverlog' --preserve-environment postgres as root without the –preserve-environment flag, it doesn't recognize pg_ctl. Otherwise, the service starts and I can connect to the DB. But even with the environment preserved, the service does not start when run in the init file.

Any clues?
Thanks!
Vic.