This came as a surprise when I came back from vacation to discover that all of a sudden can’t do this on my Linux box sqlplus / as sysdba. I was getting ORA-01017. Something like this:
[oracle@dbtest dbs]$ sqlplus / as sysdba SQL*Plus: Release 18.104.22.168.0 Production on Wed Aug 3 09:59:29 2016 Copyright (c) 1982, 2014, Oracle. All rights reserved. ERROR: ORA-01017: invalid username/password; logon denied Enter user-name: ^C [oracle@dbtest dbs]$
In my case, one of my colleagues, took the liberty to set TWO_TASK variable. After removing/unsetting the variable, all came to my desired situation.
As you may know, this TWO_TASK variable overwrites the ORACLE_SID & ORACLE_HOME variables and prohibits the local connections and is letting you to use the sqlnet path.