where is the trace file for tkprof in 11G

Hi,

Can anybody tell me where to find the trace file from tkprof? This is what I did, but there is nothing under the $ORACLE_BASE/diag/rdbms/oracle_sid/ORACLE_SID/trace/

I am using Oracle 11GR2 on Linux

ALTER SESSION SET sql_trace = true;
alter session set  tracefile_identifier ="my_trace_file";
Alter session set statistics_level=all;
alter session set max_dump_file_size='unlimited';

Thanks

George