Cron Every 12 Hours

Understanding the Expression

The cron expression 0 */12 * * * breaks down as follows:

Field	Value	Meaning
Minute	0	At minute 0
Hour	*/12	Every 12 hours
Day of month	*	Every day of the month
Month	*	Every month
Day of week	*	Every day of the week

Example Usage

Basic crontab entry

0 */12 * * * /path/to/your/script.sh

With output logging

0 */12 * * * /path/to/script.sh >> /var/log/script.log 2>&1

With monitoring

0 */12 * * * /path/to/script.sh && curl -fsS https://cronsignal.io/ping/YOUR_CHECK_ID

Common Use Cases for Every 12 Hours

• Data synchronization: Sync data between systems periodically
• Batch processing: Process accumulated records in batches
• Report generation: Generate periodic status reports
• Cleanup tasks: Remove temporary files and stale data

Platform Equivalents

The same schedule expressed across common platforms and schedulers:

Timezone Considerations

0 */12 * * * fires at 00:00 and 12:00 UTC — midnight and noon. Absolute times, not a rolling 12-hour interval.

Common Mistakes

• Only 2 runs per day: Fires at midnight and noon UTC — not "12 hours after last run". A job starting at 8 AM runs next at noon (4 hours later).
• Twice-daily output: If generating reports or files, both runs produce output. Ensure naming handles AM/PM runs to avoid overwrites.
• AWS step syntax: Use 0/12 not */12: cron(0 0/12 * * ? *).