Login as sysdba with OS authentication in Windows Machine in Oracle database

If you lost your SYS password then you can login with OS authentication in Oracle database on windows machine by editing the SQLNET.ORA file present in Oracle Home Location %ORACLE_HOME%/network/admin/sqlnet.ora and change parameter value to NTS as: SQLNET.AUTHENTICATION_SERVICES= (NTS)

Following are the steps we described with example:
1. First tried with SQLPLUS as window user as shown below:

C:\Users\Oracle>sqlplus / as sysdba
SQL*Plus: Release 18.0.0.0.0 - Production on Wed Aug 26 15:49:17 2020
Version 18.4.0.0.0
Copyright (c) 1982, 2018, Oracle. All rights reserved.
ERROR:
ORA-01017: invalid username/password; logon denied


2. IF you got the error while tried with OS authentication and you user has right of ORADBA group then you can login with OS user. Then Go the the Oracle Home Location %ORACLE_HOME%\network\admin and you find the sqlnet.ora file.
Open the SQLNET.ORA file and edit the following parameter AUTHENTICATION_SERVICES value to NTS. Save it.

SQLNET.AUTHENTICATION_SERVICES= (NONE)
to
SQLNET.AUTHENTICATION_SERVICES= (NTS)


3. Now retry with SQLPLUS to use the OS authentication

C:\Users\Oracle>sqlplus / as sysdba
SQL*Plus: Release 18.0.0.0.0 - Production on Wed Aug 26 15:49:34 2020
Version 18.4.0.0.0
Copyright (c) 1982, 2018, Oracle. All rights reserved.
Connected to:
Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
Version 18.4.0.0.0
SQL>


4. Now you can change the password of SYS user by following command if you want:
alter user sys identified by password$123