alter database open read only;
alter database open read only
*
ERROR at line 1:
ORA-10456: cannot open standby database; media recovery session may be in
progress


SQL> alter database recover managed standby database using current logfile disconnect from session;
alter database recover managed standby database using current logfile disconnect from session
*
ERROR at line 1:
ORA-01153: an incompatible media recovery is active