Trying to connect to the database locally with a different account (root) than the software owner (oracle), the error ORA-12546 is returned. User does not have sufficient privileges to perform the desired operation. The error, ora-12546, occurs due to an incorrect setting on the oracle executable.
 

Make sure the permission on the oracle executable is correct. The oracle executable permission should be:

52224 -rwsr-sr-x 1 oracle dba 53431665 Aug 10 11:07 oracle

To set permission on Oracle binary:
Logon as oracle
cd $ORACLE_HOME/bin
chmod 6755 oracle

If the issue still persists, get in touch with the Oracle support for setting the account correctly.