SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount;
ORACLE instance started.
Total System Global Area 603979776 bytes
Fixed Size 1220796 bytes
Variable Size 171970372 bytes
Database Buffers 423624704 bytes
Redo Buffers 7163904 bytes
Database mounted.
SQL> alter database archivelog;
Database altered.
SQL> alter database open;
Database altered.
SQL> select log_mode from v$database;
LOG_MODE
————
ARCHIVELOG