Insufficient Privileges with '/ as sysdba'

In 9i, I used to be able to use '/ as sysdba' on the command line to startup a database. Now in 10g I have to use 'sys/passwd as sysdba'.

Did something like os authentication change in 10g? I am using linux.

buck_at_turf:~> sqlplus '/ as sysdba'

SQL*Plus: Release 10.1.0.2.0 - Production on Thu Sep 16 09:06:09 2004

Copyright (c) 1982, 2004, Oracle. All rights reserved.

ERROR:
ORA-01031: insufficient privileges

Enter user-name:
buck_at_turf:~> w
buck_at_turf:~> sqlplus 'sys/passwd as sysdba'

SQL*Plus: Release 10.1.0.2.0 - Production on Thu Sep 16 09:06:30 2004

Copyright (c) 1982, 2004, Oracle. All rights reserved.

Connected to an idle instance.

SQL> startup
ORACLE instance started.

Total System Global Area 138412032 bytes

Fixed Size                   777796 bytes