SQL> ALTER SESSION SET sql_trace=TRUE;
SQL> ALTER SESSION SET sql_trace=FALSE;

SQL> EXEC DBMS_SESSION.set_sql_trace(sql_trace => TRUE);
SQL> EXEC DBMS_SESSION.set_sql_trace(sql_trace => FALSE);

SQL> ALTER SESSION SET EVENTS '10046 trace name context forever, level 8';
SQL> ALTER SESSION SET EVENTS '10046 trace name context off';

SQL> EXEC DBMS_SYSTEM.set_sql_trace_in_session(sid=>123, serial#=>1234, sql_trace=>TRUE);
SQL> EXEC DBMS_SYSTEM.set_sql_trace_in_session(sid=>123, serial#=>1234, sql_trace=>FALSE);

SQL> EXEC DBMS_SYSTEM.set_ev(si=>123, se=>1234, ev=>10046, le=>8, nm=>' ');
SQL> EXEC DBMS_SYSTEM.set_ev(si=>123, se=>1234, ev=>10046, le=>0, nm=>' ');

-- Available from SQL*Plus since 8i (commandline utility prior to this.
SQL> CONN sys/password AS SYSDBA; -- User must have SYSDBA.
SQL> ORADEBUG SETMYPID; -- Debug current session.
SQL> ORADEBUG SETOSPID 1234; -- Debug session with the specified OS process.
SQL> ORADEBUG SETORAPID 123456; -- Debug session with the specified Oracle process ID.

SQL> ORADEBUG EVENT 10046 TRACE NAME CONTEXT FOREVER, LEVEL 12;
SQL> ORADEBUG TRACEFILE_NAME; -- Display the current trace file.
SQL> ORADEBUG EVENT 10046 TRACE NAME CONTEXT OFF;

-- All versions, requires DBMS_SUPPORT package to be loaded.
SQL> EXEC DBMS_SUPPORT.start_trace(waits=>TRUE, binds=>FALSE);
SQL> EXEC DBMS_SUPPORT.stop_trace;

SQL> EXEC DBMS_SUPPORT.start_trace_in_session(sid=>123, serial=>1234, waits=>TRUE, binds=>FALSE);
SQL> EXEC DBMS_SUPPORT.stop_trace_in_session(sid=>123, serial=>1234);