SQL Trace is not generating file

 I am having this issue for last 4-5 days.I am trying to generate sql trace file.
I have set sql_trace in both database (through init.ora) and also in the session level.

SQL> show parameter sql_trace

NAME TYPE VALUE

---

-----------

---

sql_trace boolean TRUE
SQL> show parameter trace_enabled

NAME TYPE VALUE

---

-----------

---

trace_enabled boolean TRUE
SQL> show parameter user_dump

NAME TYPE VALUE

---

-----------

---

user_dump_dest string /oracle/admin/itst50/udump

SQL> show parameter timed_statistics

NAME TYPE VALUE

---

-----------

---

timed_statistics boolean TRUE
SQL> select * from dual;

D
-
X

SQL> 

itst50--/oracle/admin/itst50/udump>> lt