/etc/crontab文件包括下面几行:
cat /etc/crontab
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=HOME=/
# run-parts
51 * * * * root run-parts /etc/cron.hourly
24 7 * * * root run-parts /etc/cron.daily
22 4 * * 0 root run-parts /etc/cron.weekly
42 4 1 * * root run-parts /etc/cron.monthly
原文:http://www.cnblogs.com/fengjunhua/p/7736404.html