How do I change port for the postmaster?

I'm attempting to run two different postmasters on two different HP-UX
servers, servicing two different apps. The only commonality is that I'm on
one terminal.

The first starts up OK. When I attempt to start the postmaster on the
other server, I get the error,

FATAL: StreamServerPort: bind() failed: errno=226 Is another postmaster
already running on that port? If not, remove socket node
(/tmp/.s.PGSQL.5432) and retry./usr/local/pgsql/bin/postmaster: cannot
create UNIX stream port

Tried deleting the file, /tmp/.s.PGSQL.5432 but this had no effect.

Do I need to use a different port number, to run postmaster on two
different servers? If so, does anybody know how I can change the port
number? Is there something else, that I'm doing wrong?

I'm looking through the docs but can't find anything. I'd like to keep
postgres in the organization and avoid switching to (and learning) some big
commercial product like oracle!

Thanks!
Rob Wagner
Lowly Consultant,
SIAC