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crontab

Introduction​

This cheat sheet provides a quick reference for some common cron and crontab commands and concepts. cron is a job scheduler that allows you to automate tasks on Unix-like operating systems.

Cron Concepts​

Cron Syntax​

Cron jobs are defined using a syntax that specifies when and how often a job should run:

* * * * * command_to_run
| | | | |
| | | | +--- Day of the week (0 - 7) (Sunday is both 0 and 7)
| | | +----- Month (1 - 12)
| | +------- Day of the month (1 - 31)
| +--------- Hour (0 - 23)
+----------- Minute (0 - 59)

Special Characters​

Cron syntax allows for special characters:

  • *: Wildcard, matches all possible values for a field.
  • ,: Specifies a list of values.
  • -: Specifies a range of values.
  • /: Specifies a step value.

Cron Environment​

Cron jobs run in a minimal environment. You may need to specify the full path to commands and set environment variables.

Crontab Command-Line​

  • Edit the current user's crontab:

    crontab -e

  • List the current user's crontab entries:

    crontab -l

  • Remove the current user's crontab:

    crontab -r

Crontab Examples​

Schedule a Daily Backup​

0 2 * * * /path/to/backup-script.sh

This example schedules a backup script to run daily at 2:00 AM.

Run a Script Every Hour​

0 * * * * /path/to/script.sh

This example runs a script every hour at the beginning of the hour.

Schedule Weekly Maintenance​

0 3 * * 6 /path/to/maintenance-script.sh

This example schedules a maintenance script to run every Saturday at 3:00 AM.

Schedule a Monthly Report​

0 0 1 * * /path/to/report-script.sh

This example schedules a monthly report script to run on the first day of each month at midnight.

Conclusion​

This cheat sheet covers some common cron and crontab commands and concepts for scheduling and automating tasks in Unix-like operating systems. cron is a versatile tool for automating recurring tasks; refer to the official cron documentation for more in-depth information and advanced usage.