Poul Christiansen replied to this same question that you posted on the pgsql-sql list, so I'll just paste it here so other people can know.
This line will set the maximum shared memory in Linux to 64MB:
echo 67108864 > /proc/sys/kernel/shmmax
You can see your default maximum shared memory with this command:
cat /proc/sys/kernel/shmmax
You should probably set this line in /etc/rd.d/init.d/postgresql or
somewhere else, before PostgreSQL starts because the change will be set
back to the default value when Linux restarts.
