Crontab致使Linux的線程數枯竭

症狀描述：

ps -ef |grep sendmail 滿屏
ps -ef |grep postdrop 滿屏

查看log瘋狂刷屏

[root@10-10-11-141 runtime]# tail -f /var/log/maillog
Nov 12 18:00:24 10-10-11-141 postfix/postdrop[3804]: warning: mail_queue_enter: create file maildrop/634461.3804: No such file or directory
Nov 12 18:00:24 10-10-11-141 postfix/postdrop[4147]: warning: mail_queue_enter: create file maildrop/634601.4147: No such file or directory
Nov 12 18:00:24 10-10-11-141 postfix/postdrop[1741]: warning: mail_queue_enter: create file maildrop/634604.1741: No such file or directory
Nov 12 18:00:24 10-10-11-141 postfix/postdrop[1967]: warning: mail_queue_enter: create file maildrop/843229.1967: No such file or directory
Nov 12 18:00:25 10-10-11-141 postfix/postdrop[3244]: warning: mail_queue_enter: create file maildrop/135131.3244: No such file or directory
Nov 12 18:00:25 10-10-11-141 postfix/postdrop[2514]: warning: mail_queue_enter: create file maildrop/135247.2514: No such file or directory

同時/var/spool/postfix/maildrop/文件夾下出現大量簇文件

解決

使用pstree|grep crond，結果以下：

|-crond---125*[crond---sendmail---postdrop]

可見crond守護進程啓動了sendmail，進而啓動了postdrop。查看crond的配置， crontab -e，都沒有發現幾秒就啓動的程序，因此多是sendmail本身一旦郵件發送不成功，就持續從新發送而致使持續啓動postdrop，而postdrop老是執行失敗，致使持續寫入日誌到日誌文件。日誌文件增大的速率超過了logrotate的刪除頻率，因此佔據了100%的磁盤空間。而且線程數也不斷的增長。

首先停掉posfix /etc/init.d/posfix stop並刪除/var/spool/postfix/maildrop/下面的所有簇文件，釋放磁盤inode！

而後就是手起刀落幹掉sendmail和postdrop的進程，注意先幹掉postdrop子進程

kill -9 $(ps -auwx | grep postdrop | gawk -F' ' '{print $2}')
kill -9 $(ps -auwx | grep sendmail | gawk -F' ' '{print $2}')

以後還要設置crond的MAILTO爲空

[root@10-10-11-141 runtime]# cat /etc/cron.d/0hourly 
MAILTO=""
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
HOME=/
01 * * * * root run-parts /etc/cron.hourly

[root@10-10-11-141 runtime]# cat /etc/crontab 
MAILTO=""
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
HOME=/

# For details see man 4 crontabs

# Example of job definition:
# .---------------- minute (0 - 59)
# |  .------------- hour (0 - 23)
# |  |  .---------- day of month (1 - 31)
# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# |  |  |  |  |
# *  *  *  *  * user-name command to be executed

[root@10-10-11-141 runtime]# service crond restart

最後整個世界都清靜了！