Oracle start database with incorrect password

Question

I have a question regarding starting oracle database with in correct sys password.

I have provided incorrect password for sys user and I am still able to start database and execute statements. So wondering whether I have missed something while installation or this is how it is?

Any insight into this is highly appreciable, Below is the result of start database.

sqlplus

SQL*Plus: Release 11.2.0.1.0 Production on Thu Nov 15 16:50:39 2012

Copyright (c) 1982, 2009, Oracle.  All rights reserved.

Enter user-name: sys/d as sysdba
Connected to an idle instance.

SQL> startup
ORACLE instance started.

Total System Global Area  422670336 bytes
Fixed Size                  1336960 bytes
Variable Size             285215104 bytes
Database Buffers          130023424 bytes
Redo Buffers                6094848 bytes
Database mounted.

Answer 1

When your OS user is from a DBA group, you can connect AS SYSDBA with OS authentication:

Two special operating system groups control database administrator connections when using operating system authentication. These groups are generically referred to as OSDBA and OSOPER. The groups are created and assigned specific names as part of the database installation process. [..]

Membership in the OSDBA or OSOPER group affects your connection to the database in the following ways:

• If you are a member of the OSDBA group and you specify AS SYSDBA when you connect to the database, then you connect to the database with the SYSDBA system privilege.

• If you are a member of the OSOPER group and you specify AS SYSOPER when you connect to the database, then you connect to the database with the SYSOPER system privilege.

You can then use CONNECT / AS SYSDBA or even CONNECT FOO/ANYTHING AS SYSDBA, the DB will ignore the user/password.