1.命令功能

通过crontab 命令，我们可以在固定的间隔时间执⾏指定的系统指令或 shell script脚本。时间间隔的单位可以是分钟、⼩时、⽇、⽉、周及

2.常用命令参数

-e 编辑某个用户的crontab文件内容

  
  root@localhost:~# crontab -e
  # 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
  ​

-l 显示某个用户的crontab文件内容

  
  root@localhost:~# crontab -l
  # 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
  ​

-r 从/var/spool/cron⽬录中删除某个⽤户的crontab⽂件，如果不指定⽤户，则默认删除当前⽤户的crontab⽂件。（删除的是当前用户的所有定时任务）

  
  root@localhost:~# ls /var/spool/cron/crontabs/root 
  /var/spool/cron/crontabs/root
  root@localhost:~# crontab -r
  root@localhost:~# ls /var/spool/cron/crontabs/root 
  ls: cannot access '/var/spool/cron/crontabs/root': No such file or directory
  ​

3.添加命令格式

minute： 表示分钟，可以是从0到59之间的任何整数。

hour：表示小时，可以是从0到23之间的任何整数。

day：表示日期，可以是从1到31之间的任何整数。

month：表示月份，可以是从1到12之间的任何整数。

week：表示星期几，可以是从0到7之间的任何整数，这里的0或7代表星期日。

command：要执行的命令，可以是系统命令，也可以是自己编写的脚本文件。

星号（*）：代表每的意思，例如month字段如果是星号，则表示每月都执行该命令操作。

逗号（,）：表示分隔时段的意思，例如，“1,3,5,7,9”。

中杠（-）：表示一个时间范围，例如“2-6”表示“2,3,4,5,6”。