Mastering Cron: Create, Schedule, and Manage Linux Cron Jobs

What Is a Cron Timer?

Cron is a scheduling utility that automatically runs commands at specified times. Each scheduled task is called a cronjob and is defined in a crontab file.

Creating a Cronjob

To create a new cronjob, invoke the crontab command with the -e option, which opens the default editor for the crontab file: $ crontab -e If you want to specify a different editor, set the EDITOR environment variable before running the command, for example:

EDITOR=nano crontab -e

Cron Syntax

A cron expression consists of five space‑separated fields that define when the command runs:

Minute (0‑59)

Hour (0‑23, where 0 is midnight)

Day of month (1‑31)

Month (1‑12)

Day of week (0‑6, where 0 is Sunday)

The asterisk ( *) means “every”. For example, the following expression runs a backup script at minute 0 of every hour, every day: /opt/backup.sh 0 * * * Another example runs the script at 03:30 every Sunday:

/opt/backup.sh 30 3 * * 0

Shortcut Macros

Modern cron implementations support shortcut macros that replace full expressions: @hourly – at minute 0 of every hour @daily – at 00:00 each day @weekly – at 00:00 on Sunday @monthly – at 00:00 on the first day of each month

Using a macro, the same daily backup can be scheduled as:

/opt/backup.sh @daily

Stopping or Removing a Cronjob

To stop a cronjob, edit the crontab file again, delete the line containing the unwanted command, and save the file: EDITOR=nano crontab -e Alternatively, you can terminate a running process with standard Linux process‑management commands.

Automation Note

Once the crontab file is saved and the editor exits, the cron daemon automatically schedules the jobs, handling execution without further user intervention.