标题：[实践OK]由于crondtab定时任务导致大量sendmail进程的解决办法
出处：向东博客 专注WEB应用 构架之美 --- 构架之美，在于尽态极妍 | 应用之美，在于药到病除
时间：Mon, 01 Jan 2018 14:49:39 +0000
作者：jackxiang
地址：http://jackxiang.com/post/9585/

内容：
背景：Zabbix报警进程数太多报警Too many processes on servername ...。发现是Sendmail进程数太多。
ps -ef|grep sendmail|wc -l
569
-bash: /data/logs/.syshistory/bash_history.log: Read-only file system
/usr/sbin/postdrop -r
/usr/sbin/sendmail -FCronDaemon -i -odi -oem -oi -t -f root
[aio/21]
[kblockd/18]
[kondemand/0]
[kondemand/1]
[kondemand/N]


执行top的时候发现当前用户下面有很多sendmail的进程，如下图所示，发件人是crondaemon，怀疑是和定时任务有关，查看当前用户的定时任务发现有一个每分钟运行一次的定时任务，但是定时脚本是没有调用sendmail了，ps -ef | grep sendmail | wc -l 统计发现sendmail的进程数据基本上就是从服务器出故障到当前时间的分钟数。

/usr/sbin/sendmail -FCronDaemon -i -odi -oem -oi -t -f root
/usr/sbin/sendmail -FCronDaemon -i -odi -oem -oi -t -f root
/usr/sbin/sendmail -FCronDaemon -i -odi -oem -oi -t -f root


然道是crontab每次执行都会调用sendmail发邮件吗？man 5 crontab查看帮助手册的时候发现这个一段话：
In  addition  to  LOGNAME,  HOME,  and SHELL, cron(8) will look at MAILTO if it has any reason to send mail as a result of running commands in "this" crontab.  If MAILTO is defined (and non-empty), mail is sent to the user so named.  If MAILTO is defined but empty (MAILTO=""), no mail will be sent.  Otherwise mail is sent to the owner of the crontab.  This option is useful if you decide on /bin/mail instead of /usr/lib/sendmail as your mailer when you install  cron  -- /bin/mail doesnt do aliasing, and UUCP usually doesnt read its mail. If MAILFROM is defined (and non-empty), it will be used as the envelope sender address, otherwise, ‘‘root’’ will be used.


查看crontab的配置文件：
cat /etc/crontab
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
HOME=/

可以看到MAILTO这一行不为空，如果不想让它发邮件的话可以按照手册上面说的把MAILTO这一行删掉或者改为MAILTO=""

From:http://blog.51cto.com/chenql/1878182


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