正常启动时会报错，恢复步骤如下：
1、以oracle用户登录系统，sqlplus / as sysdba;
2、start mount;
3、alter database datafile '/u01/app/oracle/oradata/orcl/undotbs01.dbf' offline drop;
4、alter database open;
5、create undo tablespace undotbs2 datafile '/u01/app/oracle/oradata/orcl/undotbs02.dbf' size 200m autoextend on maxsize 10g;
6、alter system set undo_tablespace=undotbs2;
7、drop tablespace undotbs1 including contents and datafiles;