概述

在檢視oracle的v$instance檢視中發現有logins列，我們可以看下contents中對此列的定義。

LOGINS  VARCHAR2(10)    Indicates whether the instance is in unrestricted 
                        mode,allowing logins by all users (ALLOWED, or in 
                        restricted mode, allowing logins by database 
                        administrators only (RESTRICTED)

例項啟動有兩種模式，一種為allowed，一種為restricted模式。

Restricted Mode of Instance Startup

You can start an instance in restricted mode (or later alter an existing instance to be in restricted mode). This restricts connections to only those users who have been granted the RESTRICTED SESSION system privilege.

如果DBA將資料庫的狀態設定為restricted mode，那麼只能是擁有restrict許可權的使用者（受限特權的使用者），才能夠連線到資料庫進行操作。Restricted Mode（受限模式）通常用於資料庫管理員在維護資料庫的時候使用。Restricted Mode限制新的沒有許可權的使用者登入進來，但是如果一個沒有Restricted Mode許可權的使用者在設定Restricted Mode之前已經登入到了Oracle那麼該使用者仍然擁有操作資料庫的許可權，即Restricted Mode不妨礙已經登入進來的使用者繼續執行操作。
 

測試

例項的預設模式檢視

SQL> select logins from v$instance;

LOGINS
----------
ALLOWED

建立測試使用者

SQL> create user test identified by test;

User created.

SQL> grant connect,resource to test;

Grant succeeded.

使用test連線資料庫

[[email protected] ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2
 
.0.4.0 Production on Thu Jul 14 19:06:18 2016

Copyright (c) 1982, 2013, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> conn test/test
Connected.
 

將例項模式修改為restricted mode

SQL> alter system enable restricted session;

System altered.

SQL> select logins from v$instance;

LOGINS
----------
RESTRICTED

新建立連線使用test賬號連線

[[email protected] ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.4.0 Production on Thu Jul 14 19:06:18 2016

Copyright (c) 1982, 2013, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> conn test/test
ERROR:
ORA-01035: ORACLE only available to users with RESTRICTED SESSION privilege


Warning: You are no longer connected to ORACLE.

測試已經登入的test連線

SQL> conn test/test
Connected.

SQL> create table test(id number); 

Table created.

SQL> insert into test values(1);

1 row created.

SQL> commit;

Commit complete.

將許可權restricted session賦予使用者test，再次嘗試連線

SQL> grant restricted session to test;

Grant succeeded.

SQL> conn test/test
Connected.

通過以上測試，我們得知，如果想資料庫設定為Restricted Mode，只有管理員（dba）以及有restricted session許可權才可以連線使用者。在修改為 Restricted Mode後，之前連線使用者不受影響，新使用者不能連線。