Hi Suneeth,
check $ORACLE_HOME/rdbms/lib config.c which looks something like this:
/* SS_DBA_GRP defines the UNIX group ID for sqldba adminstrative access. */
/* Refer to the Installation and User's Guide for further information. */
#define SS_DBA_GRP "dba"
#define SS_OPER_GRP "oper"
char *ss_dba_grp[] = {SS_DBA_GRP, SS_OPER_GRP};
if second #define do not contain oper, but dba, then u have to modify this file as above. After modification you have to relink this executable. To relink use command:
$relink all
Hope this helps.
Regards,
Deepak Kori