Crontab day of the week syntax on Linux

A crontab is a configuration file that contains a list of commands scheduled to run at specific times. It uses the cron daemon, a time-based job scheduler in Unix-like operating systems, to execute these commands automatically.

Understanding Crontab Syntax

To create or edit a crontab job, use the following command:

crontab -e

This opens the crontab editor where you can add scheduled jobs. Each crontab entry follows a specific format with five time fields followed by the command to execute:

* * * * * command_to_execute

Crontab Time Fields

The five asterisks represent different time units in the following order:

Day of Week Syntax

The day of week field accepts both numeric and text values:

Note: Both 0 and 7 represent Sunday, providing flexibility in scheduling Sunday jobs.

Examples

Running a Job Every Sunday

To schedule a script to run every Sunday at 8:05 AM, you can use any of these formats:

5 8 * * 0 /path/to/script.sh
5 8 * * 7 /path/to/script.sh
5 8 * * Sun /path/to/script.sh

Other Day-Specific Examples

# Run backup every Monday at 2:30 AM
30 2 * * 1 /home/user/backup.sh

# Execute maintenance every Friday at 11:00 PM
0 23 * * Fri /usr/local/bin/maintenance.sh

# Send reports every Wednesday at 9:15 AM
15 9 * * Wed /opt/reports/generate_report.py

Advanced Day Scheduling

You can also use ranges and lists for more complex scheduling:

# Run Monday through Friday (weekdays)
0 9 * * 1-5 /path/to/weekday_task.sh

# Run on Monday, Wednesday, and Friday
0 18 * * 1,3,5 /path/to/selected_days.sh

# Run every other day of the week
0 12 * * */2 /path/to/every_other_day.sh

Conclusion

Understanding crontab day-of-week syntax is essential for scheduling automated tasks on specific days. The fifth field accepts values 0-7 (with both 0 and 7 representing Sunday) or three-letter abbreviations, providing flexible options for day-based job scheduling in Linux systems.