oracle@ywdb ~]$ sqlplus /as sysdba sql*plus: release 11.1.0.7.0 - production on tue apr 29 15:40:38 2014 copyright (c) 1982, 2008, oracle. all rights reserved. connected to: oracle database 11g enterprise edition release 11.1.0.7.0 - 64bit
oracle@ywdb ~]$ sqlplus /as sysdba
sql*plus: release 11.1.0.7.0 - production on tue apr 29 15:40:38 2014
copyright (c) 1982, 2008, oracle.  all rights reserved.
connected to:
oracle database 11g enterprise edition release 11.1.0.7.0 - 64bit production
with the partitioning, olap, data mining and real application testing options
sql> 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 disabled
sql> exit
disconnected from oracle database 11g enterprise edition release 11.1.0.7.0 - 64bit production
with the partitioning, olap, data mining and real application testing options
you 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 2014
copyright (c) 1982, 2008, oracle.  all rights reserved.
connected to:
oracle database 11g enterprise edition release 11.1.0.7.0 - 64bit production
with the partitioning, olap, data mining and real application testing options
sql>  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。