Crontab Generator

Generate cron expressions for scheduled tasks

Crontab Expression Generator

Quick Presets

Cron Expression Generator

Generated Crontab Line

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

Description

This cron job will run every minute.

💡Common Cron Examples

System Maintenance:

0 2 * * * /usr/sbin/logrotate
Daily log rotation at 2 AM
0 3 * * 0 /usr/sbin/weekly-maintenance
Weekly maintenance on Sundays at 3 AM
0 4 1 * * /usr/sbin/monthly-backup
Monthly backup on 1st at 4 AM

Application Tasks:

*/5 * * * * /usr/bin/check-service
Check service every 5 minutes
0 */6 * * * /usr/bin/cleanup-temp
Clean temp files every 6 hours
30 9 * * 1-5 /usr/bin/send-report
Send report weekdays at 9:30 AM

What is Crontab?

Crontab (cron table) is a Linux/Unix utility that allows you to schedule and automate repetitive tasks. It's a powerful tool for system administrators and developers to run scripts, commands, or programs at specified intervals without manual intervention.

Cron Expression Format

Minute
0-59
Hour
0-23
Day of Month
1-31
Month
1-12
Day of Week
0-6

Format: minute hour day_of_month month day_of_week command

Special Characters

Asterisk (*)

Represents "every" value:

  • * in minute field = every minute
  • * in hour field = every hour
  • * in day field = every day

Slash (/)

Specifies intervals:

  • */5 = every 5 units
  • */15 = every 15 minutes
  • */2 = every 2 hours

Comma (,)

Specifies multiple values:

  • 1,3,5 = at 1, 3, and 5
  • 0,6 = on Sunday and Saturday
  • 1,15 = on 1st and 15th

Hyphen (-)

Specifies ranges:

  • 1-5 = from 1 to 5
  • 9-17 = from 9 AM to 5 PM
  • 1-31 = every day of month

Common Use Cases

System Maintenance

Automate routine system tasks:

  • Log rotation and cleanup
  • System updates and patches
  • Backup operations
  • Disk space monitoring
  • Security scans and updates

Application Management

Schedule application-specific tasks:

  • Database maintenance and backups
  • Cache clearing and optimization
  • Report generation and distribution
  • Data synchronization
  • Performance monitoring

Business Operations

Automate business processes:

  • Daily/weekly/monthly reports
  • Data processing and analysis
  • Email notifications and alerts
  • Invoice generation
  • Customer data updates

Best Practices

  • Use Absolute Paths: Always specify full paths to scripts and commands
  • Set Proper Permissions: Ensure scripts have execute permissions (chmod +x)
  • Log Output: Redirect output to log files for debugging
  • Test Commands: Verify commands work manually before adding to crontab
  • Use Descriptive Comments: Add comments to explain what each job does
  • Monitor Execution: Check logs regularly to ensure jobs are running
  • Backup Crontab: Keep backups of your crontab configuration
  • Consider Time Zones: Be aware of system timezone settings

Troubleshooting

Common Issues

  • Script permissions not set correctly
  • Environment variables not available
  • Path issues in cron environment
  • Output not being captured
  • Time zone mismatches

Debugging Commands

  • crontab -l - List current crontab
  • crontab -e - Edit crontab
  • systemctl status cron - Check cron service
  • tail -f /var/log/cron - Monitor cron logs
  • grep CRON /var/log/syslog - View cron entries

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