Two password for "sys" user.

Question

Dear All,
I have only single database named TEST on IBM AIX / oracle 9i system. I m very much surprise that i m able to connect to that db using sys user with two password. ie. sys/sys ans sys/test.
SQL*Plus: Release 9.2.0.1.0 - Production on Tue Sep 15 09:11:55 2009
Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.
Enter user-name: sys/test as sysdba
Connected to an idle instance.
SQL> startup
ORACLE instance started.
Total System Global Area 186089336 bytes
Fixed Size 741240 bytes
Variable Size 150994944 bytes
Database Buffers 33554432 bytes
Redo Buffers 798720 bytes
Database mounted.
Database opened.
SQL> select name from v$database;
NAME
TEST
SQL> shutdown
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> conn sys/sys as sysdba
Connected to an idle instance.
SQL> startup
ORACLE instance started.
Total System Global Area 186089336 bytes
Fixed Size 741240 bytes
Variable Size 150994944 bytes
Database Buffers 33554432 bytes
Redo Buffers 798720 bytes
Database mounted.
Database opened.
SQL> select name from v$database;
NAME
TEST
i found two files in /oracle/9201/db_1/dbs folder namely 'oraTEST' and 'oraPWDTEST'. I removed 'oraTEST' file from the location then also i m able to connect with two passwd. can u plz explain the logic behind this???
SQL> conn sys/test as sysdba
Connected.
SQL> select name from v$database;
NAME
TEST
SQL> conn sys/sys as sysdba
Connected.
SQL> conn sys/test as sysdba
Connected.
SQL> select * from v$pwfile_users;
USERNAME SYSDB SYSOP
SYS TRUE TRUE
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Answer 1

The point about OS authentication for the SYS user is that the SYS user often needs to be authenticated when the database is not up and the the data dictionary cannot be interrogated. For this reason, you can't use the standard Oracle user/password setup as per "normal" users.
So the three options here are
- OS authentication
- Password file
- External authentation e.g. LDAP, etc.
To use a password file, you'll have to disable os authentication otherwise it will overrule the password file.
http://download.oracle.com/docs/cd/B28359_01/server.111/b28310/dba006.htm#ADMIN11056
http://download.oracle.com/docs/cd/B28359_01/network.111/b28531/authentication.htm#DBSEG33331