ORA-01123 cannot start online backup; media recovery not enabled

执行以下语句报错：

SQL> alter tablespace system begin backup;
ERROR at line 1:
ORA-01123: cannot start online backup; media recovery not enabled

通过查看资料发现时归档未开启，开启归档操作步骤：

SQL> alter database close normal;
Database altered.
SQL> select open_mode from v$database;
OPEN_MODE
------------------------------------------------------------
MOUNTED
SQL> alter database archivelog;
Database altered.

发现这时候要重启数据库，否则无法直接切换到读写模式：

SQL> alter database open;
alter database open
*
ERROR at line 1:
ORA-16196: database has been previously opened and closed

SQL> shutdown immediate;
ORA-01109: database not open

Database dismounted.
ORACLE instance shut down.
SQL> startup;
ORACLE instance started.
Total System Global Area 6680915968 bytes
Fixed Size                  2213936 bytes
Variable Size            3556771792 bytes
Database Buffers         3087007744 bytes
Redo Buffers               34922496 bytes
Database mounted.
Database opened.

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