Crontab Reboot: How to Execute a Job Automatically at Boot

骑猪看日落 2024-02-18 09:46 50阅读 0赞

Introduction

The Cron daemon is a Linux utility used for scheduling system tasks and processes. It uses cron tables (crontab) to store and read [scheduled jobs][].

**This tutorial will cover how you can use crontab to schedule jobs to be run at system reboot.**

Prerequisites

*  A system running Linux
 *  Access to a command line/terminal window
 *  A user account with [root or sudo privileges][]

### Crontab Command Overview ###

With the **`crontab`** command, you have full control of when and how jobs are executed. Use **`crontab`** to set job execution time down to the minute, without the need for looping and timing logic in the task.

**`crontab`** has low resource requirements since it doesn’t reserve system memory when it isn’t running.

### Crontab on Boot: Run a Cron Job at Boot Time ###

Open the cron task list by using the following command:

crontab -e

If you have multiple [text editors][] installed, the system prompts you to select an editor to update the cron task list with. Use the number in the brackets to choose your preferred option. We will be using the default option, Nano.

![Opening cron jobs ist with the crontab command][]

**Note:** Leaving the field blank and pressing enter chooses the first option available.

To run a cron job at every [system boot][], add a string called **`@reboot`** to the end of the task list. The job defined by this string runs at startup, immediately after Linux reboots.

Use the following syntax when adding a **`@reboot`** string:

@reboot [path to command] [argument1] [argument2] … [argument n]
    @reboot [part to shell script]

**Note:** Always use the full path to the job, script, or command you want to run, starting from the root.

Press **`Control + X`** to exit Nano, then **`Y`** and **`Enter`** to save any changes you made.

For example, if we wanted to have the system date written in a file called **date.txt** [when Linux restarts][], we would add the following string:

@reboot date >> ~/date.txt

If we wanted to run the backup shell at reboot, we would add:

@reboot /root/backup.sh

![Updating the cron job list][]

**Note:** In some cases, the crond service needs to be enabled on boot for the configuration to function.  
To check if the crond service is enabled, use:

sudo systemctl status cron.service

To enable this service, use:

sudo systemctl enable cron.service

### Run a Cron Job at Boot With Delay ###

To run a job with a delay after the system reboots, use the [sleep command][] when adding the **`@reboot`** string:

@reboot sleep [time in seconds] && [path to job]

If you want to create a text file with the system date five minutes after reboot, add:

@reboot sleep 300 && date >> ~/date.txt

### Remove a Reboot Command ###

Each **`@reboot`** string you add to the cron task list runs a job every time Linux restarts. If you no longer wish to run a job, remove it from the task list.

To do this, open the task list using the **`crontab -e`** command. Scroll down to the bottom to review the jobs you added.

To remove a task from the list, delete the appropriate line from the appropriate string. Press **`Control + X`** to exit Nano, then **`Y`** and **`Enter`** to save changes.

**Note:** Learn more about the [Linux at command][], the alternative for cron job for scheduling jobs.

Conclusion

After following this tutorial, you understand how to use crontab to schedule jobs to run at system reboot.

For more ways to schedule jobs in crontab, check out our [guide to setting up cron jobs][].

[scheduled jobs]: https://phoenixnap.com/glossary/job-scheduling
[root or sudo privileges]: https://phoenixnap.com/kb/linux-sudo-command
[text editors]: https://phoenixnap.com/kb/best-linux-text-editors-for-coding
[Opening cron jobs ist with the crontab command]: https://image.dandelioncloud.cn/pgy_files/images/2024/02/18/befc2d0da2a54acb9293f0454d5b7392.png
[system boot]: https://phoenixnap.com/glossary/boot-definition
[when Linux restarts]: https://phoenixnap.com/kb/restart-linux-using-command-prompt
[Updating the cron job list]: https://image.dandelioncloud.cn/pgy_files/images/2024/02/18/c609dc7d22374567aa6524c36a9108ef.png
[sleep command]: https://phoenixnap.com/kb/linux-sleep
[Linux at command]: https://phoenixnap.com/kb/linux-at-command
[guide to setting up cron jobs]: https://phoenixnap.com/kb/set-up-cron-job-linux