In unusual circumstances, a previous instance might not have been shut down cleanly.
For example, one of the instance’s processes might not have terminated properly. In
such situations, the database can return an error during normal instance startup. To
resolve this problem, you must terminate all remnant Oracle processes of the previous
instance before starting the new instance

异常情况下强制启动
管理员需要在启动实例前手工结束系统中残留的 Oracle 进程才能解决这个问题