隐式参数_trace_files_public决定了Oracle产生的trace文件是否公开，该参数默认值为FALSE，也就是非DBA/OINSTALL组的用户是没有权限读取数据库产生的trace文件的;在某些场合中我们需要让非DBA组的用户也能访问trace文件，就可以通过修改该参数实现。请看下面的例子:
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SQL> 
select 
* 
from 
v$version;
 
BANNER
----------------------------------------------------------------
Oracle 
Database 
10g Enterprise Edition Release 10.2.0.4.0 - 64bi
PL/SQL Release 10.2.0.4.0 - Production
CORE    10.2.0.4.0      Production
TNS 
for 
Linux: Version 10.2.0.4.0 - Production
NLSRTL Version 10.2.0.4.0 - Production
 
SQL> col 
name 
for 
a20
SQL> col value 
for 
a20
SQL> col describ 
for 
a40
SQL> 
SELECT 
x.ksppinm 
NAME
, y.ksppstvl VALUE, x.ksppdesc describ
  
2   
FROM 
SYS.x$ksppi x, SYS.x$ksppcv y
  
3   
WHERE 
x.inst_id = USERENV (
'Instance'
)
  
4   
AND 
y.inst_id = USERENV (
'Instance'
)
  
5   
AND 
x.indx = y.indx
  
6  
AND 
x.ksppinm 
LIKE 
'%_trace_files_public%'
  
7  
order 
by 
x.ksppinm;
 
NAME                 
VALUE                DESCRIB
-------------------- -------------------- ----------------------------------------
_trace_files_public  
FALSE                
Create 
publicly accessible trace files
 
SQL> oradebug setmypid;
Statement processed.
SQL> oradebug ipc;
Information written 
to 
trace file.
SQL> oradebug tracefile_name;
/s01/10gdb/admin/YOUYUS/udump/youyus_ora_10268.trc
SQL> !ls -l /s01/10gdb/admin/YOUYUS/udump/youyus_ora_10268.trc
-rw-r
----- 1 maclean oinstall 4206 Aug 11 20:51 /s01/10gdb/admin/YOUYUS/udump/youyus_ora_10268.trc
/*所产生的trace文件权限为640,非oinstall组用户无权限读取该文件*/
 
SQL> 
alter 
system 
set 
"_trace_files_public"
=
true
;
alter 
system 
set 
"_trace_files_public"
=
true
                 
*
ERROR 
at 
line 1:
ORA-02095: specified initialization parameter cannot be modified
/*修改该参数需要重启实例*/
 
SQL> 
alter 
system 
set 
"_trace_files_public"
=
true 
scope=spfile;
 
System altered.
 
SQL> startup 
force
;
ORACLE instance started.
 
Total System 
Global 
Area 1577058304 bytes
Fixed 
Size                  
2084264 bytes
Variable 
Size             
922747480 bytes
Database 
Buffers          637534208 bytes
Redo Buffers               14692352 bytes
Database 
mounted.
Database 
opened.
 
SQL> oradebug setmypid;
Statement processed.
SQL> oradebug ipc;
Information written 
to 
trace file.
SQL> oradebug tracefile_name;
/s01/10gdb/admin/YOUYUS/udump/youyus_ora_10430.trc
SQL> ! ls -l /s01/10gdb/admin/YOUYUS/udump/youyus_ora_10430.trc
-rw-r
--r-- 1 maclean oinstall 5471 Aug 11 20:54 /s01/10gdb/admin/YOUYUS/udump/youyus_ora_10430.trc
/*other组用户也具有了读权限*/
 
SQL> ! ls -l /s01/10gdb/admin/YOUYUS/
total 24
drwxr-x
--- 2 maclean oinstall 4096 Aug 11 20:56 adump
drwxr-x
--- 2 maclean oinstall 4096 Aug 11 20:54 bdump
drwxr-x
--- 2 maclean oinstall 4096 Aug  5 21:35 cdump
drwxr-x
--- 2 maclean oinstall 4096 Aug  5 21:36 dpdump
drwxr-x
--- 2 maclean oinstall 4096 Aug  5 21:37 pfile
drwxr-x
--- 2 maclean oinstall 4096 Aug 11 20:54 udump
/*请注意修改_trace_files_public为
true
,并不会修改trace所在目录的权限，Oracle默认建立bdump/udump等trace目录时分配的权限为750,other组用户无法进入这些目录，需要修改目录权限为755,即o+r+x*/
 
SQL> ! chmod o+r+x /s01/10gdb/admin/YOUYUS/*dump
 
SQL>  ! ls -l /s01/10gdb/admin/YOUYUS/
total 24
drwxr-xr-x 2 maclean oinstall 4096 Aug 11 20:56 adump
drwxr-xr-x 2 maclean oinstall 4096 Aug 11 20:54 bdump
drwxr-xr-x 2 maclean oinstall 4096 Aug  5 21:35 cdump
drwxr-xr-x 2 maclean oinstall 4096 Aug  5 21:36 dpdump
drwxr-x
--- 2 maclean oinstall 4096 Aug  5 21:37 pfile
drwxr-xr-x 2 maclean oinstall 4096 Aug 11 20:54 udump
 
/*需要注意的另一点是修改_trace_files_public参数并不会引起既有的trace文件的权限被修改，典型的例子是alert log告警日志*/
[maclean@rh2 bdump]$ ls -l
total 20
-rw-r
----- 1 maclean oinstall 12971 Aug 11 21:17 alert_YOUYUS.log
-rw-r
--r-- 1 maclean oinstall   690 Aug 11 21:12 youyus_lgwr_10514.trc
 
SQL> 
SELECT 
x.ksppinm 
NAME
, y.ksppstvl VALUE, x.ksppdesc describ
  
2   
FROM 
SYS.x$ksppi x, SYS.x$ksppcv y
  
3   
WHERE 
x.inst_id = USERENV (
'Instance'
)
  
4   
AND 
y.inst_id = USERENV (
'Instance'
)
  
5   
AND 
x.indx = y.indx
  
6  
AND 
x.ksppinm 
LIKE 
'%_trace_files_public%'
  
7  
order 
by 
x.ksppinm;
 
NAME                 
VALUE                DESCRIB
-------------------- -------------------- ----------------------------------------
_trace_files_public  
FALSE                
Create 
publicly accessible trace files
 
SQL> 
alter 
system 
set 
"_trace_files_public"
=
true 
scope=spfile;
 
System altered.
 
SQL> startup 
force
;
ORACLE instance started.
 
Total System 
Global 
Area 1577058304 bytes
Fixed 
Size                  
2084264 bytes
Variable 
Size             
922747480 bytes
Database 
Buffers          637534208 bytes
Redo Buffers               14692352 bytes
Database 
mounted.
Database 
opened.
SQL> !ls -l
total 32
-rw-r
----- 1 maclean oinstall 21189 Aug 11 21:20 alert_YOUYUS.log
-rw-r
--r-- 1 maclean oinstall   690 Aug 11 21:12 youyus_lgwr_10514.trc
-rw-r
--r-- 1 maclean oinstall   690 Aug 11 21:20 youyus_lgwr_11136.trc