PROBLEM:

We have restored a standalone database from a rac database, and while doing open resetlog, getting below error.

SQL> alter database open resetlogs;
alter database open resetlogs
*
ERROR at line 1:
ORA-38856: cannot mark instance UNNAMED_INSTANCE_2 (redo thread 2) as enabled

SOLUTION:

SQL> alter system set "_no_recovery_through_resetlogs"=TRUE scope=both;

System altered.

SQL> shutdown immediate;
ORA-01109: database not open

SQL> alter database open resetlogs;

Database altered.