How to find current init.ora file

Question

I have 2 issues:
Issue 1:--
I have some 4-5 init.ora file which are created by some other user and facing difficulties to find exact init.ora which is used by my oracle 9.2 database. same thing for spfile.
Is there any way so that i can find the currently use init.ora file?
Issue 2:
I want to change init.ora file parameters for the oracle9.2(siebel).
Presently default it is showing optimizer_mode=CHOOSE
I have tried to change to RULE but not refelecting after database restart.
at session level i can modify but i want permanent change and for thius i tried with
user SYS as SYSDBA with
ALTER SYSTEM SET optimizer_mode=RULE;
but getting following Oracle erroe message
ORA-02096 specified initialization parameter is not modifiable with this option
Cause: Though the initialization parameter is modifiable, it cannot be modified using the specified command.
Action: Check the Oracle9i Database Administrator's Guide for information about under what scope the parameter may be modified
How we can make changes in init.ora file?
Regards
Junu

Answer 1

As far as I know, there's no possible way to find out which parameter file was used to start instance. And, even if it was, I don't really see much sense in it because parameter file is a client-side file, and usually it required to start up Oracle instance remotely.
In principle, parameter files are obsolete beasts, consider using server parameter file (SPFILE) instead. And, for SPFILE, it's pretty easy to find out its location:
SQL> show parameter pfile
NAME                                 TYPE        VALUE
spfile                               string      %ORACLE_HOME%\DATABASE\SPFILE%
                                                 ORACLE_SID%.ORAAs for your ORA-02096 error, you have two opportunities to resolve it.
If you decided to use SPFILE, create one (for example, using CREATE SPFILE FROM PFILE command), start your instance with SPFILE then issue:
ALTER SYSTEM SET optimizer_mode=RULE  SCOPE = SPFILE;and bounce your instance.
If you still wish to use old-style parameter file, you have to add corresponding setting into that file manually (it's a plain text file in fact) and restart instance.
Regards.
P.S.: Why do you want to enforce rule-based optimizer by the way?...