[CentOS] boot.log no message on CENTOS 5.X?

I found CENTOS 5.X boot.log is empty but CENTOS 4.X it does have messages in it.

cd /var/log
# ls -al boot*
-rw------- 1 root root 0 Feb 21 04:02 boot.log
-rw------- 1 root root 0 Feb 14 04:02 boot.log.1
-rw------- 1 root root 0 Feb  7 04:02 boot.log.2
-rw------- 1 root root 0 Jan 31 04:02 boot.log.3
-rw------- 1 root root 0 Jan 24 04:02 boot.log.4

Does anyone know how to setup boot.log include boot message on CENTOS 5.X?

Thanks.