oracle@ywdb ~]$ sqlplus "/as sysdba"SQL*Plus: Release 11.1.0.7.0 - Production on Tue Apr 29 15:40:38 2014Copyright (c) 1982, 2008, Oracle.  All rights reserved.Connected to:Oracle Database 11g Enterprise Edition Release 11.1.0.7.0 - 64bit ProductionWith the Partitioning, OLAP, Data Mining and Real Application Testing optionsSQL> alter user sys identified by oracle  2  ;User altered.SQL> alter user sys identified by oracle;User altered.SQL> alter user sys identified by manager;User altered.SQL> grant sysdba to system;grant sysdba to system*ERROR at line 1:ORA-01994: GRANT failed: password file missing or disabledSQL> exitDisconnected from Oracle Database 11g Enterprise Edition Release 11.1.0.7.0 - 64bit ProductionWith the Partitioning, OLAP, Data Mining and Real Application Testing optionsYou have new mail in /var/spool/mail/oracle[oracle@ywdb ~]$ orapwd file=$ORACLE_HOME/dbs/orapw$ORACLE_SID password=‘manager‘ entries=10[oracle@ywdb ~]$ sqlplus "/as sysdba"SQL*Plus: Release 11.1.0.7.0 - Production on Tue Apr 29 15:49:03 2014Copyright (c) 1982, 2008, Oracle.  All rights reserved.Connected to:Oracle Database 11g Enterprise Edition Release 11.1.0.7.0 - 64bit ProductionWith the Partitioning, OLAP, Data Mining and Real Application Testing optionsSQL>  grant sysdba to system;Grant succeeded.SQL> 

system用户没有dba权限的。

但是想授予他权限的话，

那么必须添加一个密码文件。

然后才能授予。