configure shmmax on MAC OS X

Hi, all,

I have got a new MaC OS G5 with 8GB RAM. So i tried to increase
the shmmax in Kernel so that I can take advantage of the RAM.

I searched the web and read the manual for PG7.4 chapter 16.5.1.
After that, I edited /etc/rc file:

sysctl -w kern.sysv.shmmax=4294967296 // byte
sysctl -w kern.sysv.shmmin=1
sysctl -w kern.sysv.shmmni=32
sysctl -w kern.sysv.shmseg=8
sysctl -w kern.sysv.shmall=1048576 //4kpage

for 4G shared RAM.

Then I changed postgresql.conf:
shared_buffer=100000 //could be bigger?

and restart the machine and postgres server. To my surprise, postgres
server wouldn't
start, saying that the requested shared memory exceeds kernel's shmmax.

My suspision is that the change i made in /etc/rc does not take
effect.Is there a way
to check it?  Is there an
up limit for how much RAM can be allocated for shared buffer in MAC OS
X? Or
is there something wrong with my calculation in numbers?

Thanks a lot!

Qing