可能很多朋友都遇到过这样的情况，在UNIX/Linux上定期清理Oracle日志文件夹时可能删除到仍被后台进程open着的trace文件，即某些后台进程一直持有着这些”被已经误删了的“打开文件的描述符(fd)，这种情况下文件系统上该文件实际占用的空间是不会被释放的，这就造成使用df命令查看文件系统剩余空间和用du命令查看文件夹空间使用量时数值不一致的问题。此外因为是后台进程持有这些打开文件描述符，所以我们无法像kill服务进程一样来解决该问题(部分后台进程是可以kill的，不建议这样做)。oradebug是sqlplus中威力强大的debug命令,我们可以通过该命令发起多种trace/dump，其中也包括了close_trace事件；close_trace事件可以让指定进程关闭其正持有的trace文件。
下面我们就来演示下相关操作:
[maclean@rh2 ~]$ ps -ef|grep ora_|grep -v grep
maclean 7281 1 0 16:35 ? 00:00:00 ora_pmon_PROD
maclean 7283 1 0 16:35 ? 00:00:00 ora_psp0_PROD
maclean 7285 1 0 16:35 ? 00:00:00 ora_mman_PROD
maclean 7287 1 0 16:35 ? 00:00:00 ora_dbw0_PROD
maclean 7289 1 0 16:35 ? 00:00:00 ora_lgwr_PROD
maclean 7291 1 0 16:35 ? 00:00:00 ora_ckpt_PROD
maclean 7293 1 0 16:35 ? 00:00:00 ora_smon_PROD
maclean 7295 1 0 16:35 ? 00:00:00 ora_reco_PROD
maclean 7297 1 0 16:35 ? 00:00:00 ora_cjq0_PROD
maclean 7299 1 0 16:35 ? 00:00:00 ora_mmon_PROD
maclean 7301 1 0 16:35 ? 00:00:00 ora_mmnl_PROD
maclean 7303 1 0 16:35 ? 00:00:00 ora_d000_PROD
maclean 7305 1 0 16:35 ? 00:00:00 ora_s000_PROD
maclean 7313 1 0 16:35 ? 00:00:00 ora_qmnc_PROD
maclean 7430 1 0 16:35 ? 00:00:00 ora_q000_PROD
maclean 7438 1 0 16:36 ? 00:00:00 ora_q001_PROD
/* lgwr是著名的Oracle后台进程，在这个启动的实例中其系统进程号为7289*/
[maclean@rh2 ~]$ ls -l /proc/7289/fd /* linux上的proc文件系统可以很方便我们探测进程信息*/
total 0
lr-x------ 1 maclean oinstall 64 Jul 26 16:38 0 -> /dev/null
lr-x------ 1 maclean oinstall 64 Jul 26 16:38 1 -> /dev/null
lr-x------ 1 maclean oinstall 64 Jul 26 16:38 10 -> /dev/zero
lr-x------ 1 maclean oinstall 64 Jul 26 16:38 11 -> /dev/zero
lr-x------ 1 maclean oinstall 64 Jul 26 16:38 12 -> /s01/rac10g/rdbms/mesg/oraus.msb
lrwx------ 1 maclean oinstall 64 Jul 26 16:38 13 -> /s01/rac10g/dbs/hc_PROD.dat
lrwx------ 1 maclean oinstall 64 Jul 26 16:38 14 -> /s01/rac10g/dbs/lkPROD
lrwx------ 1 maclean oinstall 64 Jul 26 16:38 15 -> /s01/rac10g/oradata/PROD/controlfile/o1_mf_64q6xphj_.ctl
lrwx------ 1 maclean oinstall 64 Jul 26 16:38 16 -> /s01/rac10g/flash_recovery_area/PROD/controlfile/o1_mf_64q6xpms_.ctl
lrwx------ 1 maclean oinstall 64 Jul 26 16:38 17 -> /s01/rac10g/oradata/PROD/onlinelog/o1_mf_1_64q6xrsr_.log
lrwx------ 1 maclean oinstall 64 Jul 26 16:38 18 -> /s01/rac10g/flash_recovery_area/PROD/onlinelog/o1_mf_1_64q6xsoy_.log
lrwx------ 1 maclean oinstall 64 Jul 26 16:38 19 -> /s01/rac10g/oradata/PROD/onlinelog/o1_mf_2_64q6xths_.log
l-wx------ 1 maclean oinstall 64 Jul 26 16:38 2 -> /s01/rac10g/admin/PROD/bdump/prod_lgwr_7289.trc
lrwx------ 1 maclean oinstall 64 Jul 26 16:38 20 -> /s01/rac10g/flash_recovery_area/PROD/onlinelog/o1_mf_2_64q6xv9o_.log
lrwx------ 1 maclean oinstall 64 Jul 26 16:38 21 -> /s01/rac10g/oradata/PROD/onlinelog/o1_mf_3_64q6xw1b_.log
lrwx------ 1 maclean oinstall 64 Jul 26 16:38 22 -> /s01/rac10g/flash_recovery_area/PROD/onlinelog/o1_mf_3_64q6xwv0_.log
lrwx------ 1 maclean oinstall 64 Jul 26 16:38 23 -> /s01/rac10g/oradata/PROD/datafile/o1_mf_system_64q6wd5j_.dbf
lrwx------ 1 maclean oinstall 64 Jul 26 16:38 24 -> /s01/rac10g/oradata/PROD/datafile/o1_mf_undotbs1_64q6wd7f_.dbf
lrwx------ 1 maclean oinstall 64 Jul 26 16:38 25 -> /s01/rac10g/oradata/PROD/datafile/o1_mf_sysaux_64q6wd5m_.dbf
lrwx------ 1 maclean oinstall 64 Jul 26 16:38 26 -> /s01/rac10g/oradata/PROD/datafile/o1_mf_users_64q6wd89_.dbf
lrwx------ 1 maclean oinstall 64 Jul 26 16:38 27 -> /s01/rac10g/oradata/PROD/datafile/o1_mf_temp_64q6xyox_.tmp
lr-x------ 1 maclean oinstall 64 Jul 26 16:38 28 -> /s01/rac10g/rdbms/mesg/oraus.msb
lr-x------ 1 maclean oinstall 64 Jul 26 16:38 3 -> /dev/null
lr-x------ 1 maclean oinstall 64 Jul 26 16:38 4 -> /dev/null
l-wx------ 1 maclean oinstall 64 Jul 26 16:38 5 -> /s01/rac10g/admin/PROD/udump/prod_ora_7279.trc
l-wx------ 1 maclean oinstall 64 Jul 26 16:38 6 -> /s01/rac10g/admin/PROD/bdump/alert_PROD.log
lrwx------ 1 maclean oinstall 64 Jul 26 16:38 7 -> /s01/rac10g/dbs/lkinstPROD (deleted)
lrwx------ 1 maclean oinstall 64 Jul 26 16:38 8 -> /s01/rac10g/dbs/hc_PROD.dat
l-wx------ 1 maclean oinstall 64 Jul 26 16:38 9 -> /s01/rac10g/admin/PROD/bdump/alert_PROD.log
/*可以看到lgwr进程相关trace文件为/s01/rac10g/admin/PROD/bdump/prod_lgwr_7289.trc，对应打开文件描述符为2*/
[maclean@rh2 ~]$ ls -lh /s01/rac10g/admin/PROD/bdump/prod_lgwr_7289.trc
-rw-r----- 1 maclean oinstall 1.7M Jul 26 16:37 /s01/rac10g/admin/PROD/bdump/prod_lgwr_7289.trc
[maclean@rh2 ~]$ rm -f /s01/rac10g/admin/PROD/bdump/prod_lgwr_7289.trc
/*尝试删除该trace文件*/
[maclean@rh2 ~]$ ls -l /proc/7289/fd|grep lgwr
l-wx------ 1 maclean oinstall 64 Jul 26 16:38 2 -> /s01/rac10g/admin/PROD/bdump/prod_lgwr_7289.trc (deleted)
/*文件已处在deleted状态，但lgwr进程仍持有该文件相关的文件描述符，这个时候该文件占有的空间并不会被释放*/
[maclean@rh2 ~]$ lsof|grep lgwr
oracle 7289 maclean 2w REG 8,2 1702391 3867134 /s01/rac10g/admin/PROD/bdump/prod_lgwr_7289.trc (deleted)
[maclean@rh2 ~]$ sqlplus / as sysdba
SQL*Plus: Release 10.2.0.5.0 - Production on Mon Jul 26 17:03:04 2010
Copyright (c) 1982, 2010, Oracle. All Rights Reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL> oradebug setospid 7289;
Oracle pid: 6, Unix process pid: 7289, image: oracle@rh2 (LGWR)
SQL> oradebug flush; /*写出trace buffer内容到trace文件*/
Statement processed.
SQL> oradebug close_trace;
Statement processed.
/*close_trace能够释放指定Oracle进程正打开着的文件，To close the current trace file use*/
SQL> host
[maclean@rh2 ~]$ lsof|grep lgwr
[maclean@rh2 ~]$ ls -l /proc/7289/fd/|grep lgwr
[maclean@rh2 ~]$
/* 从进程相关的fd文件夹中查找不到原来的trace文件；close_trace命令成功释放了该文件，并回收了磁盘空间。*/