第三种情况：
　　参数SQLNET.AUTHENTICATION_SERVICES 设置为  NONE 或NTS ----------------屏蔽操作系统认证都启用口令认证
[oracle@tyger admin]$ vim sqlnet.ora
NAME.DIRECTORY_PATH=(tnsnames，ezconnect)
SQLNET.AUTHENTICATION_SERVICES=(NTS)
[oracle@tyger admin]$ sqlplus / as sysdba
SQL*Plus: Release 10.2.0.1.0 - Production on Fri Feb 28 10:36:35 2014
Copyright (c) 1982， 2005， Oracle.  All rights reserved.
ERROR:
ORA-01031: insufficient privileges
[oracle@tyger admin]$ sqlplus sys/oracle@ORCL as sysdba
SQL*Plus: Release 10.2.0.1.0 - Production on Fri Feb 28 10:36:52 2014
Copyright (c) 1982， 2005， Oracle.  All rights reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning， OLAP and Data Mining options
SYS@ORCL>
　　第四种情况：
　　当数据库屏蔽了操作系统认证，启用口令认证方式的话，需要检查remote_login_passwordfile参数，如果该参数设置为NONE，该值表示不使用口令文件，因此，此时数据库将不能登录
　　解决办法：启动操作系统认证，登录数据库后将remote_login_passwordfile参数修改EXCLUSIVE，然后再屏蔽操作系统认证，启用口令认证。
　　> remote_login_passwordfile参数可以设置为3个值 none、exclusive、shared
[oracle@tyger admin]$ cat sqlnet.ora
NAME.DIRECTORY_PATH=(tnsnames，ezconnect)
SQLNET.AUTHENTICATION_SERVICES=(NTS)
[oracle@tyger admin]$ sqlplus sys/oracle@ORCL as sysdba
SQL*Plus: Release 10.2.0.1.0 - Production on Fri Feb 28 10:48:15 2014
Copyright (c) 1982， 2005， Oracle.  All rights reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning， OLAP and Data Mining options
SYS@ORCL>show parameter remote
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
remote_archive_enable                string      true
remote_dependencies_mode             string      TIMESTAMP
remote_listener                      string
remote_login_passwordfile            string      EXCLUSIVE
remote_os_authent                    boolean     FALSE
remote_os_roles                      boolean     FALSE
SYS@ORCL>alter system set remote_login_passwordfile=none scope=spfile;
System altered.
　　---静态参数，重启数据库生效
SYS@ORCL>shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SYS@ORCL>startup
ORA-12514: TNS:listener does not currently know of service requested in connect descriptor
[oracle@tyger admin]$ vim sqlnet.ora
NAME.DIRECTORY_PATH=(tnsnames，ezconnect)
#SQLNET.AUTHENTICATION_SERVICES=(NTS)
[oracle@tyger admin]$ sqlplus / as sysdba
SQL*Plus: Release 10.2.0.1.0 - Production on Fri Feb 28 10:57:25 2014
Copyright (c) 1982， 2005， Oracle.  All rights reserved.
Connected to an idle instance.
SYS@ORCL>startup
ORACLE instance started.
Total System Global Area  285212672 bytes
Fixed Size                  1218992 bytes
Variable Size              96470608 bytes
Database Buffers          184549376 bytes
Redo Buffers                2973696 bytes
Database mounted.
Database opened.
SYS@ORCL>show parameter remote
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
remote_archive_enable                string      true
remote_dependencies_mode             string      TIMESTAMP
remote_listener                      string
remote_login_passwordfile            string      NONE
remote_os_authent                    boolean     FALSE
remote_os_roles                      boolean     FALSE
SYS@ORCL>alter system set remote_login_passwordfile=exclusive scope=spfile;
System altered.
SYS@ORCL>shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SYS@ORCL>startup
ORACLE instance started.
Total System Global Area  285212672 bytes
Fixed Size                  1218992 bytes
Variable Size              96470608 bytes
Database Buffers          184549376 bytes
Redo Buffers                2973696 bytes
Database mounted.
Database opened.
SYS@ORCL>show parameter remote
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
remote_archive_enable                string      true
remote_dependencies_mode             string      TIMESTAMP
remote_listener                      string
remote_login_passwordfile            string      EXCLUSIVE
remote_os_authent                    boolean     FALSE
remote_os_roles                      boolean     FALSE
SYS@ORCL>exit
Disconnected from Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning， OLAP and Data Mining options
[oracle@tyger admin]$ sqlplus sys/oracle@ORCL as sysdba
SQL*Plus: Release 10.2.0.1.0 - Production on Fri Feb 28 11:04:16 2014
Copyright (c) 1982， 2005， Oracle.  All rights reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning， OLAP and Data Mining options
SYS@ORCL>