Crontab in Ubuntu automates shell scripts. Here is my earlier post on this topic. In Ubuntu or any other Linux operating system, the crontab allows for edits only to root users. The sudo users usually are root users.
How to schedule jobs in crontab
Explained the detailed steps that you need to schedule a job in crontab.
Ubuntu Crontab commands
Here are four ridiculously useful commands that you can use while working with Crontab. These are list, edit, backup, and replace commands.
List command
You can view jobs with the list command.
$sudo crontab -l # browse
Edit command
You can edit the Crontab with the edit command.
$sudo crontab -e #edit
Creating jobs in Ubuntu Crontab
To show how to add a cron job, I have added a simple job, which creates a directory at the specified time.

The explanation for example cron job
The job runs at 15 minutes, at 20 hours, on 30th, July (7th ), and Saturday, execute command is mkdir srini. A directory of srini creates after running this crontab command.
Backup and Replace commands
Backup command
Here is a command you can use to take the backup of Crontab.
Replace command
Taking backup is the best practice before making changes to the Crontab. The following command replaces the current set of jobs with the jobs in the file crontab.new:
$ crontab -r > crontab.new
Timezone in Crontab
Please note that Crontab triggers scripts according to your operating system’s Timezone.
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