startup open read only; dataguard ORA-01665: control file is not a standby control file

SYSTEM2
SQL> startup open read only;
ORACLE instance started.

Total System Global Area  313860096 bytes
Fixed Size                  1336232 bytes
Variable Size             205524056 bytes
Database Buffers          100663296 bytes
Redo Buffers                6336512 bytes
Database mounted.
Database opened.

while starting standby and verified

SQL> alter database recover managed standby database using current logfile disconnect from session;

ERROR at line 1:
ORA-01665: control file is not a standby control file


SQL> SELECT database_role FROM v$database;

DATABASE_ROLE
----------------
PRIMARY

again changed and started with normal

SQL> shut immediate;

Database closed.

Database dismounted.

ORACLE instance shut down.

SQL> startup;

ORACLE instance started.

Total System Global Area  313860096 bytes

Fixed Size                  1336232 bytes

Variable Size             205524056 bytes

Database Buffers          100663296 bytes

Redo Buffers                6336512 bytes

Database mounted.

Database opened.

SQL> SELECT database_role FROM v$database;

DATABASE_ROLE

----------------

PRIMARY

SYSTEM1

SQL> SELECT database_role FROM v$database;

DATABASE_ROLE

----------------

PHYSICAL STANDBY

SQL> shut immediate;

Database closed.

Database dismounted.

ORACLE instance shut down.

SQL> startup open read only;

ORACLE instance started.

Total System Global Area  313860096 bytes

Fixed Size                  1336232 bytes

Variable Size             255855704 bytes

Database Buffers           50331648 bytes

Redo Buffers                6336512 bytes

Database mounted.

Database opened.

SQL> SELECT database_role FROM v$database;

DATABASE_ROLE

----------------

PHYSICAL STANDBY

SQL> alter database recover managed standby database using current logfile disconnect from session;

Database altered.

SQL> !ps -ef|grep mrp

oracle    5277     1  0 17:11 ?        00:00:00 ora_mrp0_sony

oracle    5283  5001  0 17:11 pts/1    00:00:00 /bin/bash -c ps -ef|grep mrp

oracle    5285  5283  0 17:11 pts/1    00:00:00 grep mrp