Auditing oracle server

Auditing is a default feature of the Oracle server. The initialization parameters that influence its behaviour can be displayed using the SHOW PARAMETER SQL*Plus command.
SQL> SHOW PARAMETER AUDIT

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
audit_file_dest string C:\ORACLE\PRODUCT\10.2.0\ADMIN
\DB10G\ADUMP
audit_sys_operations boolean FALSE
audit_trail string NONE
SQL>
Auditing is disabled by default, but can enabled by setting the AUDIT_TRAIL static parameter, which has the following allowed values.
AUDIT_TRAIL = { none | os | db | db,extended | xml | xml,extended }
The following list provides a description of each setting:
•none or false - Auditing is disabled.
•db or true - Auditing is enabled, with all audit records stored in the database audit trial (SYS.AUD$).
•db,extended - As db, but the SQL_BIND and SQL_TEXT columns are also populated.
•xml- Auditing is enabled, with all audit records stored as XML format OS files.
•xml,extended - As xml, but the SQL_BIND and SQL_TEXT columns are also populated.
•os- Auditing is enabled, with all audit records directed to the operating system's audit trail.
Note. In Oracle 10g Release 1, db_extended was used in place of db,extended. The XML options are new to Oracle 10g Release 2.

The AUDIT_SYS_OPERATIONS static parameter enables or disables the auditing of operations issued by users connecting with SYSDBA or SYSOPER privileges, including the SYS user. All audit records are written to the OS audit trail.

The AUDIT_FILE_DEST parameter specifies the OS directory used for the audit trail when the os, xml and xml,extended options are used. It is also the location for all mandatory auditing specified by the AUDIT_SYS_OPERATIONS parameter.

To enable auditing and direct audit records to the database audit trail, we would do the following.
SQL> ALTER SYSTEM SET audit_trail=db SCOPE=SPFILE;

System altered.

SQL> SHUTDOWN
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> STARTUP
ORACLE instance started.

Total System Global Area 289406976 bytes
Fixed Size 1248600 bytes
Variable Size 71303848 bytes
Database Buffers 213909504 bytes
Redo Buffers 2945024 bytes
Database mounted.
Database opened.
SQL>