Merge pull request #22689 from lujun9972/add-MjAyMTA3MjYgSG93IHRvIHVzZSBjcm9uIG9uIExpbnV4Lm1kCg==

自动选题[tech]: 20210726 How to use cron on Linux

sources/tech/20210726 How to use cron on Linux.md

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+[#]: subject: (How to use cron on Linux)
+[#]: via: (https://opensource.com/article/21/7/cron-linux)
+[#]: author: (Seth Kenlon https://opensource.com/users/seth)
+[#]: collector: (lujun9972)
+[#]: translator: ( )
+[#]: reviewer: ( )
+[#]: publisher: ( )
+[#]: url: ( )
+
+How to use cron on Linux
+======
+The cron system is a method to automatically run commands on a schedule.
+![Cron expression][1]
+
+The cron system is a method to automatically run commands on a schedule. A scheduled job is called a _cronjob_, and it’s created in a file called a _crontab_. It’s the easiest and oldest way for a computer user to automate their computer.
+
+### Writing a cronjob
+
+To create a cronjob, you edit your `crontab` using the `-e` option:
+
+
+```
+`$ crontab -e`
+```
+
+This opens your crontab your default text editor. To set the text editor explicitly, use the `EDITOR` [environment variable][2]:
+
+
+```
+`$ EDITOR=nano crontab -e`
+```
+
+### Cron syntax
+
+To schedule a cronjob, you provide the command you want your computer to execute, followed by a cron expression. The cron expression schedules when the command gets run:
+
+  * minute (0 to 59)
+
+  * hour (0 to 23, with 0 being midnight)
+
+  * day of month (1 to 31)
+
+  * month (1 to 12)
+
+  * day of week (0 to 6, with Sunday being 0)
+
+
+
+
+An asterisk (`*`) in a field translates to "every." For example, this expression runs a backup script at the 0th minute of _every_ hour on _every_ day of _every_ month:
+
+
+```
+`/opt/backup.sh 0 * * * *`
+```
+
+This expression runs a backup script at 3:30 AM on Sunday:
+
+
+```
+`/opt/backup.sh 30 3 * * 0`
+```
+
+### Simplified syntax
+
+Modern cron implementations accept simplified macros instead of a cron expression:
+
+  * `@hourly` runs at the 0th minute of every hour of every day
+
+  * `@daily` runs at the 0th minute of the 0th hour of every day
+
+  * `@weekly` runs at the 0th minute of the 0th hour on Sunday
+
+  * `@monthly` runs at the 0th minute of the 0th hour on the first day of the month
+
+
+
+
+For example, this crontab line runs a backup script every day at midnight:
+
+
+```
+`/opt/backup.sh @daily`
+```
+
+### How to stop a cronjob
+
+Once you've started a cronjob, it's designed to run on schedule forever. To stop a cronjob once you've started it, you must edit your crontab, remove the line that triggers the job, and then save the file.
+
+
+```
+`$ EDITOR=nano crontab -e`
+```
+
+To stop a job that's actively running, [use standard Linux process commands][3] to stop a running process.
+
+### It’s automated
+
+Once you’ve written your crontab, save the file and exit your editor. Your cronjob has been scheduled, so cron does the rest.
+
+--------------------------------------------------------------------------------
+
+via: https://opensource.com/article/21/7/cron-linux
+
+作者：[Seth Kenlon][a]
+选题：[lujun9972][b]
+译者：[译者ID](https://github.com/译者ID)
+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://opensource.com/users/seth
+[b]: https://github.com/lujun9972
+[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/cron-splash.png?itok=AoBigzts (Cron expression)
+[2]: https://opensource.com/article/19/8/what-are-environment-variables
+[3]: https://opensource.com/article/18/5/how-kill-process-stop-program-linux