Database time zone version is 18. It is older than current release time zone version 26

[oracle@raca1 12.2.0]$ sqlplus / as sysdba

SQL*Plus: Release 12.2.0.1.0 Production on Tue Apr 18 16:15:07 2017

Copyright (c) 1982, 2016, Oracle.  All rights reserved.

Connected to:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production

SQL> set serveroutput on
SQL> SELECT PROPERTY_NAME, SUBSTR(property_value, 1, 30) value
  2  FROM DATABASE_PROPERTIES
  3  WHERE PROPERTY_NAME LIKE 'DST_%'
  4  ORDER BY PROPERTY_NAME;

PROPERTY_NAME                VALUE
--------------------------------------------------------------------------------
DST_PRIMARY_TT_VERSION        18
DST_SECONDARY_TT_VERSION    0
DST_UPGRADE_STATE            NONE

SQL> purge dba_recyclebin;

DBA Recyclebin purged.

SQL> TRUNCATE TABLE SYS.DST$TRIGGER_TABLE;

Table truncated.

SQL> TRUNCATE TABLE sys.dst$affected_tables;

Table truncated.

SQL> TRUNCATE TABLE sys.dst$error_table;

Table truncated.

SQL> EXEC DBMS_APPLICATION_INFO.SET_CLIENT_INFO('upg_tzv')

PL/SQL procedure successfully completed.

SQL> alter session set "_with_subquery"=materialize;

Session altered.

SQL> alter session set "_simple_view_merging"=TRUE;

Session altered.

SQL> EXEC DBMS_DST.BEGIN_UPGRADE(26);
BEGIN DBMS_DST.BEGIN_UPGRADE(26); END;

*
ERROR at line 1:
ORA-56926: database must be in UPGRADE mode in order to start an upgrade window
ORA-06512: at "SYS.DBMS_SYS_ERROR", line 79
ORA-06512: at "SYS.DBMS_DST", line 1241
ORA-06512: at line 1

SQL> quit
Disconnected from Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production
[oracle@raca1 12.2.0]$ sqlplus / as sysdba

SQL*Plus: Release 12.2.0.1.0 Production on Tue Apr 18 16:24:19 2017

Copyright (c) 1982, 2016, Oracle.  All rights reserved.

Connected to:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production

SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.

Total System Global Area 7.8920E+10 bytes
Fixed Size                 12169704 bytes
Variable Size            7516196376 bytes
Database Buffers         4.5366E+10 bytes
Redo Buffers              256262144 bytes
In-Memory Area           2.5770E+10 bytes
Database mounted.
SQL> alter database open upgrade;

Database altered.

SQL> EXEC DBMS_DST.BEGIN_UPGRADE(26); 

PL/SQL procedure successfully completed.

SQL> SELECT * FROM sys.dst$error_table;

no rows selected

SQL> SELECT PROPERTY_NAME, SUBSTR(property_value, 1, 30) value
  2  FROM DATABASE_PROPERTIES
  3  WHERE PROPERTY_NAME LIKE 'DST_%'
  4  ORDER BY PROPERTY_NAME;

PROPERTY_NAME                VALUE
-------------------------------------
DST_PRIMARY_TT_VERSION        26
DST_SECONDARY_TT_VERSION    18
DST_UPGRADE_STATE            UPGRADE

SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area 7.8920E+10 bytes
Fixed Size                 12169704 bytes
Variable Size            7516196376 bytes
Database Buffers         4.5366E+10 bytes
Redo Buffers              256262144 bytes
In-Memory Area           2.5770E+10 bytes
Database mounted.
Database opened.
SQL> SELECT OWNER, TABLE_NAME, UPGRADE_IN_PROGRESS FROM ALL_TSTZ_TABLES where UPGRADE_IN_PROGRESS='YES';
OWNER                     TABLE_NAME                          UPG
------------------------- ----------------------------------- ---
GSMADMIN_INTERNAL         AQ$_CHANGE_LOG_QUEUE_TABLE_S        YES
APEX_040200               WWV_FLOW_DEBUG_MESSAGES2            YES
APEX_040200               WWV_FLOW_WORKSHEET_NOTIFY           YES
APEX_040200               WWV_FLOW_FEEDBACK_FOLLOWUP          YES
APEX_050000               WWV_FLOW_WORKSHEET_NOTIFY           YES
IX                        AQ$_ORDERS_QUEUETABLE_S             YES
IX                        AQ$_ORDERS_QUEUETABLE_L             YES
GSMADMIN_INTERNAL         AQ$_CHANGE_LOG_QUEUE_TABLE_L        YES
APEX_050000               WWV_FLOW_FEEDBACK_FOLLOWUP          YES
APEX_050000               WWV_FLOW_DEBUG_MESSAGES             YES
IX                        AQ$_STREAMS_QUEUE_TABLE_L           YES
APEX_040200               WWV_FLOW_DEBUG_MESSAGES             YES
APEX_050000               WWV_FLOW_FEEDBACK                   YES
IX                        AQ$_STREAMS_QUEUE_TABLE_S           YES
APEX_040200               WWV_FLOW_FEEDBACK                   YES
APEX_050000               WWV_FLOW_DEBUG_MESSAGES2            YES

SQL> alter session set "_with_subquery"=materialize;

Session altered.

SQL> alter session set "_simple_view_merging"=TRUE;

Session altered.

SQL> set serveroutput on
SQL> VAR numfail number
SQL> BEGIN
  2  DBMS_DST.UPGRADE_DATABASE(:numfail,
  3  parallel => TRUE,
  4  log_errors => TRUE,
  5  log_errors_table => 'SYS.DST$ERROR_TABLE',
  6  log_triggers_table => 'SYS.DST$TRIGGER_TABLE',
  7  error_on_overlap_time => FALSE,
  8  error_on_nonexisting_time => FALSE);
  9  DBMS_OUTPUT.PUT_LINE('Failures:'|| :numfail);
  10 END;
  11  /
Table list: "APEX_040200"."WWV_FLOW_FEEDBACK"
Number of failures: 0
Table list: "APEX_040200"."WWV_FLOW_DEBUG_MESSAGES2"
Number of failures: 0
Table list: "IX"."AQ$_STREAMS_QUEUE_TABLE_S"
Number of failures: 0
Table list: "IX"."AQ$_ORDERS_QUEUETABLE_S"
Number of failures: 0
Table list: "GSMADMIN_INTERNAL"."AQ$_CHANGE_LOG_QUEUE_TABLE_S"
Number of failures: 0
Table list: "APEX_040200"."WWV_FLOW_WORKSHEET_NOTIFY"
Number of failures: 0
Table list: "APEX_050000"."WWV_FLOW_WORKSHEET_NOTIFY"
Number of failures: 0
Table list: "APEX_050000"."WWV_FLOW_DEBUG_MESSAGES"
Number of failures: 0
Table list: "APEX_050000"."WWV_FLOW_DEBUG_MESSAGES2"
Number of failures: 0
Table list: "APEX_040200"."WWV_FLOW_DEBUG_MESSAGES"
Number of failures: 0
Table list: "APEX_040200"."WWV_FLOW_FEEDBACK_FOLLOWUP"
Number of failures: 0
Table list: "APEX_050000"."WWV_FLOW_FEEDBACK"
Number of failures: 0
Table list: "APEX_050000"."WWV_FLOW_FEEDBACK_FOLLOWUP"
Number of failures: 0
Table list: "IX"."AQ$_ORDERS_QUEUETABLE_L"
Number of failures: 0
Table list: "IX"."AQ$_STREAMS_QUEUE_TABLE_L"
Number of failures: 0
Table list: "GSMADMIN_INTERNAL"."AQ$_CHANGE_LOG_QUEUE_TABLE_L"
Number of failures: 0
Failures:0

PL/SQL procedure successfully completed.

SQL> SELECT * FROM sys.dst$error_table;

no rows selected

SQL> VAR fail number
SQL> BEGIN
  2  DBMS_DST.END_UPGRADE(:fail);
  3  DBMS_OUTPUT.PUT_LINE('Failures:'|| :fail);
  4  END;
  5  /
An upgrade window has been successfully ended.
Failures:0

PL/SQL procedure successfully completed.

SQL> SELECT PROPERTY_NAME, SUBSTR(property_value, 1, 30) value
  2  FROM DATABASE_PROPERTIES
  3  WHERE PROPERTY_NAME LIKE 'DST_%'
  4  ORDER BY PROPERTY_NAME;

PROPERTY_NAME                VALUE
--------------------------------------------------------------------------------
DST_PRIMARY_TT_VERSION        26
DST_SECONDARY_TT_VERSION    0
DST_UPGRADE_STATE            NONE

SQL> SELECT * FROM v$timezone_file;

FILENAME                VERSION     CON_ID
-------------------- ---------- ----------
timezlrg_26.dat              26          0