How to unmount oracle database?
Yes, it's possible. 

SQL&gt; alter database close;

Database altered.

SQL&gt; select open_mode from v$database;

OPEN_MODE
--------------------
MOUNTED

SQL&gt; alter database dismount;

Database altered.

SQL&gt; select open_mode from v$database;
select open_mode from v$database
                      *
ERROR at line 1:
ORA-01507: database not mounted