Solution that worked for me.
SQL> shutdown immediate ORA-01109: database not open Database dismounted. ORACLE instance shut down. SQL> startup mount ORACLE instance started. Total System Global Area 530288640 bytes Fixed Size 2131120 bytes Variable Size 310381392 bytes Database Buffers 209715200 bytes Redo Buffers 8060928 bytes Database mounted. SQL> ALTER SYSTEM SET "_allow_resetlogs_corruption"= TRUE SCOPE = SPFILE; SQL> ALTER SYSTEM SET undo_management=MANUAL SCOPE = SPFILE; SQL> shutdown immediate ORA-01109: database not open Database dismounted. ORACLE instance shut down. SQL> startup mount ORACLE instance started. Total System Global Area 530288640 bytes Fixed Size 2131120 bytes Variable Size 310381392 bytes Database Buffers 209715200 bytes Redo Buffers 8060928 bytes Database mounted. SQL> alter database open resetlogs; Database altered. SQL> CREATE UNDO TABLESPACE undo1 datafile '<ora_data_path>undo1_1.dbf' size 200m autoextend on maxsize unlimited; Tablespace created. SQL> ALTER SYSTEM SET undo_tablespace = undo1 SCOPE=spfile; System altered. SQL> alter system set undo_management=auto scope=spfile; System altered. SQL> shutdown immediate SQL> startup