crontab循环定时任务

一 crond服务管理与访问控制

service crond restart

chkconfig crond on

[root@localhost ~]# service crond status

Redirecting to /bin/systemctl status crond.service

● crond.service - Command Scheduler

Loaded: loaded (/usr/lib/systemd/system/crond.service; enabled; vendor preset: enabled)

Active: active (running) since Tue 2017-08-08 18:37:40 CST; 57min ago

Main PID: 1189 (crond)

CGroup: /system.slice/crond.service

└─1189 /usr/sbin/crond -n

 

Aug 08 18:37:40 localhost.localdomain systemd[1]: Started Command Scheduler.

Aug 08 18:37:40 localhost.localdomain systemd[1]: Starting Command Scheduler...

Aug 08 18:37:41 localhost.localdomain crond[1189]: (CRON) INFO (RANDOM_DELAY will be scaled with...d.)

Aug 08 18:37:45 localhost.localdomain crond[1189]: (CRON) INFO (running with inotify support)

Hint: Some lines were ellipsized, use -l to show in full.

 

二 访问控制

 

 

三 用户的crontab设置

crontab [选项]

选项：

-e：编辑contab定时任务

-l：查询crontab任务

-r：删除当前用户所有的crontab任务

[root@localhost etc]# crontab -e

进入crontab编辑界面。会打开vim编辑你的工作。

* * * * * 执行的任务

 

四 5个*号的含义

 
 

 

五 特殊符号

 

 

六 常用命令

crontab -l

查看root用户的crontab任务

crontab -r

删除root用户的所有定时任务

 

七 实战

*/1 * * * * echo 111 >> /root/test

5 5 * * 2 /sbin/shutdown -r now

0 5 1,10,15 * * /root/sh/autobak.sh

[root@localhost ~]# crontab -l

*/1 * * * * echo 111 >> /root/test1

5 5 * * 2 /sbin/shutdown -r now

0 5 1,10,15 * * /root/sh/autobak.sh

[root@localhost ~]# crontab -r

[root@localhost ~]# crontab -l

no crontab for root

 

八 crontab注意事项

1、六个选项都不能为空，必须填写，如果不确定使用“*”代表任意时间。

2、crontab定时任务，最小有效时间是分钟，最大时间范围是月。像2018年某时执行，3点30分30秒这样的时间都不认识。

3、在定义时间时，日期和星期最好不要在一条定时任务中出现，因为他们都是以天为单位，非常容易让管理员混乱。

4、在定时任务中，不管是直接写命令，还是脚本中写命令，最好都用绝对路径。

 

九 举例

 

 

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