How to startup the database server?

Hi all,
I am a freshman of PostgreSQL, My env: PG 8.4 on CentOS,I follow the
document in the offical site to startup the db server. Here's what I do
below, the database cluster is ready, but I can't start the database server.

[root(at)testbox ~]# service postgresql initdb
Data directory is not empty! [FAILED]

[root(at)testbox ~]# service postgresql start
Starting postgresql service: [FAILED]

-bash-4.1$ postgres -D /var/lib/pgsql/data
-bash-4.1$ ps -ef |grep postgres
root 2710 2585 0 21:52 pts/1 00:00:00 su - postgres
postgres 2711 2710 0 21:52 pts/1 00:00:00 -bash
postgres 2752 2711 0 21:55 pts/1 00:00:00 ps -ef
postgres 2753 2711 0 21:55 pts/1 00:00:00 grep postgres

-bash-4.1$ postgres -D /var/lib/pgsql/data > binlog 2>&1 &
-bash-4.1$ ps -ef |grep postgres
root 2710 2585 0 21:52 pts/1 00:00:00 su - postgres
postgres 2711 2710 0 21:52 pts/1 00:00:00 -bash
postgres 2768 2711 1 21:59 pts/1 00:00:00 ps -ef
postgres 2769 2711 0 21:59 pts/1 00:00:00 grep postgres

I wonder why I can't start the database? Do I have some place to see the
log file. Hope anybody can help me. Thanks.
--
Best wishes,

Jason Ma