open user session in backgroup with shell script

Hi,
for installation of oracle need to set shared memory value for default project.
below code we are using to set these values.
#!/bin/sh
echo "set noexec_user_stack=1" >> /etc/system
echo "set semsys:seminfo_semmni=100" >> /etc/system
echo "set semsys:seminfo_semmns=1024" >> /etc/system
echo "set semsys:seminfo_semmsl=256" >> /etc/system
echo "set semsys:seminfo_semvmx=32767" >> /etc/system
echo "set shmsys:shminfo_shmmax=4294967295" >> /etc/system
echo "set shmsys:shminfo_shmmin=1" >> /etc/system
echo "set shmsys:shminfo_shmmni=100" >> /etc/system
echo "set shmsys:shminfo_shmseg=10" >> /etc/system
echo "* *" >> /etc/system
where as above code dosenot available immediatly  and need to to user prctl to set shared memory.
prctl -n project.max-shm-memory -v 400gb -r -i project default
but this command require default project user session to on. else it raise an below error.
prctl: default: No controllable process found in task, project, or zone.
to resolve this error i decide to open user session in backgroud.
su oracle&
but this won't work while executing it from shell script.
OS : solaris 10
give any pointer to reolve this.

thanks and regards
Sachin