SQL> startup mount;
ORACLE instance started.

Total System Global Area  814227456 bytes
Fixed Size                  2257640 bytes
Variable Size             528485656 bytes
Database Buffers          281018368 bytes
Redo Buffers                2465792 bytes
Database mounted.
SQL> alter tablespace system rename to system01;
alter tablespace system rename to system01
*
ERROR at line 1:
ORA-01109: database not open


SQL> alter database open;

Database altered.

SQL> alter tablespace system rename to system01;
alter tablespace system rename to system01
*
ERROR at line 1:
ORA-00712: cannot rename system tablespace


SQL>