在创建自动任务之前需要安装的安装包：
cron

使用crontab来对当前用户的定时任务进行编辑
crontab -u //设定某个用户的cron服务，一般root用户在执行这个命令的时候需要此参数
crontab -l //列出当前(某个)用户cron服务的详细内容
crontab -r //删除当前(某个)用户的cron服务
crontab -e //编辑当前(某个)用户的cron服务

这里使用root创建的用户，所以直接在root用户下，执行crontab -e编辑好以后然后退出编辑器即可。
如果不放心还可以执行以下/etc/init.d/cron restart

编辑好以后的脚本如下

# Edit this file to introduce tasks to be run by cron.
#
# Each task to run has to be defined through a single line
# indicating with different fields when the task will be run
# and what command to run for the task
#
# To define the time you can provide concrete values for
# minute (m), hour (h), day of month (dom), month (mon),
# and day of week (dow) or use '*' in these fields (for 'any').#
# Notice that tasks will be started based on the cron's system
# daemon's notion of time and timezones.
#
# Output of the crontab jobs (including errors) is sent through
# email to the user the crontab file belongs to (unless redirected).
#
# For example, you can run a backup of all your user accounts
# at 5 a.m every week with:
# 0 5 * * 1 tar -zcf /var/backups/home.tgz /home/
#
# For more information see the manual pages of crontab(5) and cron(8)
#
# m h  dom mon dow   command
25 22 * * 4 /var/auto_script/db_bak/dbbak.sh /var/auto_script/db_bak/dbname.txt 1 >> /var/auto_script/db_bak/autoworker_log.txt

其中的25代表时间的25分钟
22代表时间的22点
4代表每周星期4
/var/auto_script/db_bak/dbbak.sh /var/auto_script/db_bak/dbname.txt 1 >> /var/auto_script/db_bak/autoworker_log.txt 则是命令行

对于cron自身的配置来说，他的配置放在/etc/crontab，内容如下：

# /etc/crontab: system-wide crontab
# Unlike any other crontab you don't have to run the `crontab'
# command to install the new version when you edit this file
# and files in /etc/cron.d. These files also have username fields,
# that none of the other crontabs do.

SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin

# m h dom mon dow user	command
51 * * * * root cd / && run-parts --report /etc/cron.hourly
40 1 * * * root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.daily )
48 5 * * 7 root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly )
28 2 23 * * root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.monthly )
#

对于cron的配置来说，尽量不要去修改，网上有些文章说，如果要执行周期性任务，可以到/etc/cron.*目录下保存脚本，我这边看到的是，大部分都是系统类任务；最好不要去这样做。混淆了脚本的分类很麻烦