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KevinSJ Translating
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A Beginners Guide To Cron Jobs
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======
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**Cron** is one of the most useful utility that you can find in any Unix-like operating system. It is used to schedule commands at a specific time. These scheduled commands or tasks are known as “Cron Jobs”. Cron is generally used for running scheduled backups, monitoring disk space, deleting files (for example log files) periodically which are no longer required, running system maintenance tasks and a lot more. In this brief guide, we will see the basic usage of Cron Jobs in Linux.
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### The Beginners Guide To Cron Jobs
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The typical format of a cron job is:
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```
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Minute(0-59) Hour(0-24) Day_of_month(1-31) Month(1-12) Day_of_week(0-6) Command_to_execute
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```
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Just memorize the cron job format or print the following illustration and keep it in your desk.
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![][2]
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In the above picture, the asterisks refers the specific blocks of time.
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To display the contents of the **crontab** file of the currently logged in user:
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```
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$ crontab -l
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```
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To edit the current user’s cron jobs, do:
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```
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$ crontab -e
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```
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If it is the first time, you will be asked to editor to edit the jobs.
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```
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no crontab for sk - using an empty one
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Select an editor. To change later, run 'select-editor'.
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1. /bin/nano <---- easiest
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2. /usr/bin/vim.basic
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3. /usr/bin/vim.tiny
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4. /bin/ed
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Choose 1-4 [1]:
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```
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Choose any one that suits you. Here it is how a sample crontab file looks like.
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![][3]
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In this file, you need to add your cron jobs.
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To edit the crontab of a different user, for example ostechnix, do:
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```
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$ crontab -u ostechnix -e
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```
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Let us see some examples.
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To run a cron job **every minute** , the format should be like below.
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```
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* * * * * <command-to-execute>
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```
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To run cron job every 5 minute, add the following in your crontab file.
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```
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*/5 * * * * <command-to-execute>
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```
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To run a cron job at every quarter hour (every 15th minute), add this:
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```
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*/15 * * * * <command-to-execute>
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```
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To run a cron job every hour at 30 minutes, run:
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```
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30 * * * * <command-to-execute>
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```
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You can also define multiple time intervals separated by commas. For example, the following cron job will run three times every hour, at minutes 0, 5 and 10:
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```
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0,5,10 * * * * <command-to-execute>
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```
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Run a cron job every half hour:
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```
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*/30 * * * * <command-to-execute>
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```
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Run a job every hour:
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```
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0 * * * * <command-to-execute>
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```
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Run a job every 2 hours:
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```
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0 */2 * * * <command-to-execute>
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```
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Run a job every day (It will run at 00:00):
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```
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0 0 * * * <command-to-execute>
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```
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Run a job every day at 3am:
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```
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0 3 * * * <command-to-execute>
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```
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Run a job every sunday:
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```
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0 0 * * SUN <command-to-execute>
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```
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Or,
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```
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0 0 * * 0 <command-to-execute>
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```
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It will run at exactly at 00:00 on Sunday.
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Run a job on every day-of-week from Monday through Friday i.e every weekday:
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```
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0 0 * * 1-5 <command-to-execute>
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```
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The job will start at 00:00.
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Run a job every month:
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```
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0 0 1 * * <command-to-execute>
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```
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Run a job at 16:15 on day-of-month 1:
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```
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15 16 1 * * <command-to-execute>
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```
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Run a job at every quarter i.e on day-of-month 1 in every 3rd month:
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```
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0 0 1 */3 * <command-to-execute>
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```
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Run a job on a specific month at a specific time:
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```
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5 0 * 4 * <command-to-execute>
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```
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The job will start at 00:05 in April.
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Run a job every 6 months:
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```
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0 0 1 */6 * <command-to-execute>
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```
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This cron job will start at 00:00 on day-of-month 1 in every 6th month.
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Run a job every year:
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```
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0 0 1 1 * <command-to-execute>
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```
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This cron job will start at 00:00 on day-of-month 1 in January.
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We can also use the following strings to define job.
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@reboot Run once, at startup. @yearly Run once a year. @annually (same as @yearly). @monthly Run once a month. @weekly Run once a week. @daily Run once a day. @midnight (same as @daily). @hourly Run once an hour.
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For example, to run a job every time the server is rebooted, add this line in your crontab file.
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```
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@reboot <command-to-execute>
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```
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To remove all cron jobs for the current user:
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```
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$ crontab -r
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```
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There is also a dedicated website named [**crontab.guru**][4] for learning cron jobs examples. This site provides a lot of cron job examples.
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For more details, check man pages.
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```
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$ man crontab
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```
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And, that’s all for now. At this point, you might have a basic understanding of cron jobs and how to use them in real time. More good stuffs to come. Stay tuned!!
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Cheers!
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--------------------------------------------------------------------------------
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via: https://www.ostechnix.com/a-beginners-guide-to-cron-jobs/
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作者：[SK][a]
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选题：[lujun9972](https://github.com/lujun9972)
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]:https://www.ostechnix.com/author/sk/
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[1]:data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7
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[2]:http://www.ostechnix.com/wp-content/uploads/2018/05/cron-job-format-1.png
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[3]:http://www.ostechnix.com/wp-content/uploads/2018/05/cron-jobs-1.png
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[4]:https://crontab.guru/
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227
translated/tech/20180504 A Beginners Guide To Cron Jobs.md
Normal file
227
translated/tech/20180504 A Beginners Guide To Cron Jobs.md
Normal file
@ -0,0 +1,227 @@
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Cron 任务入门指南
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======
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** Cron **是您可以在任何类 Unix 操作系统中找到的最有用的实用程序之一。它用于安排命令在特定时间执行。这些预定的命令或任务被称为 “Cron 任务”。Cron 通常用于运行计划备份，监视磁盘空间，定期删除不再需要的文件（例如日志文件），运行系统维护任务等等。在本简要指南中，我们将看到 Linux 中 Cron 任务 的基本用法。
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Cron 任务入门指南
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cron 任务的典型格式是：
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```
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Minute(0-59) Hour(0-24) Day_of_month(1-31) Month(1-12) Day_of_week(0-6) Command_to_execute
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```
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只需记住 cron 任务的格式或打印下面的插图并将其放在你桌面上即可。
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![][2]
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在上图中，星号表示特定的时间块。
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要显示当前登录用户的 ** crontab ** 文件的内容：
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```
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$ crontab -l
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```
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要编辑当前用户的 cron 任务，请执行以下操作：
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```
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$ crontab -e
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```
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如果这是第一次编辑此文件，你将需要使用编辑器来编辑此文件。
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```
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no crontab for sk - using an empty one
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Select an editor. To change later, run 'select-editor'.
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1. /bin/nano <---- easiest
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||||
2. /usr/bin/vim.basic
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||||
3. /usr/bin/vim.tiny
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||||
4. /bin/ed
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||||
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Choose 1-4 [1]:
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```
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选择适合你的编辑器。这里是一个示例crontab文件的样子。
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![][3]
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在这个文件中，你需要添加你的 cron 任务s。
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要编辑其他用户的crontab，例如 ostechnix，请执行：
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```
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$ crontab -u ostechnix -e
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```
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让我们看看一些例子。
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要 **每分钟** 执行一次 cron 任务 , 需使用如下格式.
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```
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* * * * * <command-to-execute>
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```
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要每5分钟运行一次cron 任务，请在crontab文件中添加以下内容。
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```
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*/5 * * * * <command-to-execute>
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```
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要在每 1/4 个小时（每15分钟）运行一次 cron 任务，请添加以下内容：
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```
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*/15 * * * * <command-to-execute>
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```
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要每小时的第30分钟运行一次 cron 任务，请运行：
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```
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30 * * * * <command-to-execute>
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```
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您还可以使用逗号定义多个时间间隔。例如，以下 cron 任务 每小时运行三次，分别在第 0, 5 和 10 分钟运行：
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```
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0,5,10 * * * * <command-to-execute>
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```
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每半小时运行一次 cron 任务：
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```
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*/30 * * * * <command-to-execute>
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```
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每小时运行一次：
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```
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0 * * * * <command-to-execute>
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```
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每2小时运行一次：
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```
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0 */2 * * * <command-to-execute>
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```
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每天运行一项（在00:00运行）：
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```
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0 0 * * * <command-to-execute>
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```
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每天凌晨3点运行：
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```
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0 3 * * * <command-to-execute>
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```
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每周日运行：
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```
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0 0 * * SUN <command-to-execute>
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```
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或使用，
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```
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0 0 * * 0 <command-to-execute>
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```
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它将在每周日的午夜 00:00 运行。
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星期一至星期五每天运行一次，亦即每个工作日运行一次：
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```
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0 0 * * 1-5 <command-to-execute>
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```
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这项工作将于00:00开始。
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每个月运行一次：
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```
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0 0 1 * * <command-to-execute>
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```
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于每月第1天的16:15运行：
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```
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15 16 1 * * <command-to-execute>
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```
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每季度运行一次，亦即每隔3个月的第1天运行：
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```
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0 0 1 */3 * <command-to-execute>
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```
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在特定月份的特定时间运行：
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```
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5 0 * 4 * <command-to-execute>
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```
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每个四月的 00:05 运行。
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每6个月运行：
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```
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0 0 1 */6 * <command-to-execute>
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```
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这个定时任务将在每六个月的第一天的 00:00 运行。
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每年运行：
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```
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0 0 1 1 * <command-to-execute>
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```
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这项 cron 任务将于 1 月份的第一天的 00:00 运行。
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我们也可以使用以下字符串来定义任务。
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@reboot 在每次启动时运行一次。 @yearly 每年运行一次。 @annually（和 @yearly 一样）。 @monthly 每月运行一次。 @weekly 每周运行一次。 @daily 每天运行一次。 @midnight （和 @daily 一样）。 @hourly 每小时运行一次。
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例如，要在每次重新启动服务器时运行任务，请将此行添加到您的 crontab 文件中。
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```
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@reboot <command-to-execute>
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```
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要删除当前用户的所有 cron 任务：
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```
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$ crontab -r
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|
||||
```
|
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|
||||
还有一个名为 [** crontab.guru **] [4] 的专业网站，用于学习 cron 任务示例。这个网站提供了很多 cron 任务的例子。
|
||||
|
||||
有关更多详细信息，请查看手册页。
|
||||
```
|
||||
$ man crontab
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|
||||
```
|
||||
|
||||
那么，就是这样。到此为止，您应该对 cron 任务以及如何在世使用它们有了一个基本的了解。后续还会介绍更多的优秀工具。敬请关注！！
|
||||
|
||||
干杯!
|
||||
|
||||
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://www.ostechnix.com/a-beginners-guide-to-cron-任务s/
|
||||
|
||||
作者：[SK][a]
|
||||
选题：[lujun9972](https://github.com/lujun9972)
|
||||
译者：[译者KevinSJ](https://github.com/KevinSJ)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]:https://www.ostechnix.com/author/sk/
|
||||
[1]:data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7
|
||||
[2]:http://www.ostechnix.com/wp-content/uploads/2018/05/cron-任务-format-1.png
|
||||
[3]:http://www.ostechnix.com/wp-content/uploads/2018/05/cron-任务s-1.png
|
||||
[4]:https://crontab.guru/
|
||||
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