Getting ORA-01017: invalid username/password in non-CDB database
Remote (through listener) SYSDBA authentication requies a passwordfile.


Make sure remote_login_passwordfile is set to EXCLUSIVE or SHARED.
Create the password file at ${ORACLE_HOME}/dbs/orapw${ORACLE_SID} as:


orapwd file=${ORACLE_HOME}/dbs/orapw${ORACLE_SID}

This will prompt for a password, then it will create the password file. After that, you can log in remotely as SYSDBA.

PS:

This version uses OS authentication:

$ sqlplus sys/dolan123 as sysdba


As long as you try connecting locally as SYSDBA with a user that is member of the OSDBA group (defined at install time, typically dba), you can type any password, because you will be authenticated based on your group membership, not the password. Successfully logging in with the above does not necessarily means that the SYS password is dolan123.