unable to attach to share memory segment

unable to attach to share memory segment

redhat7.3上安装oracle9i,在createing and staritng oracle instance时出现:
unable to attach to share memory segment
    我只有256M,可以安装吗?shmmax的值是怎么计算出来的?      
你的内存总容量可以从计算机开机自检时得到,如320M为327680K,把327680乘1024就为shmmax的值,按照ORACLE发行的安装指导书上,shmmax起码要在200M以上,会算了吗?