Cron every 30 minutes
*/30 * * * * — Twice an hour, at :00 and :30 — 48 runs a day. 0,30 * * * * is identical.
Runs
Try one
The same schedule in every dialect
| Where | Expression | |
|---|---|---|
| Linux / Unix crontab, Kubernetes, GitHub Actions | */30 * * * * | explain |
| Quartz Scheduler | 0 0/30 * ? * * | explain |
| AWS EventBridge | cron(0/30 * * * ? *) rate(30 minutes) | explain |
Spring @Scheduled | 0 */30 * * * * | explain |
| Jenkins | H/30 * * * * | H calculator |
systemd timer OnCalendar= | *-*-* *:00/30:00 | test |
AWS rate(30 minutes) repeats at a fixed interval from when the rule or schedule was created, so it is not aligned to the clock the way the cron() form is.
Things to know
- To run at :15 and :45 instead, list them:
15,45 * * * *. - Every 90 minutes cannot be written as one standard cron line, because steps restart every hour. It needs two lines:
0 0-21/3 * * *and30 1-22/3 * * *.
Variations
| Expression | Runs |
|---|---|
| 0,30 * * * * | the same schedule, as a list |
| 15,45 * * * * | at quarter past and quarter to |
| */30 9-17 * * 1-5 | every 30 minutes during office hours on weekdays |
How to use this schedule
- Open your crontab with
crontab -e(or the scheduler's config file). - Add a line with the expression followed by the command:
*/30 * * * * /usr/local/bin/job.sh. Use absolute paths — cron runs with a minimalPATH. - Save. cron picks the change up automatically; check the next run times above, in the time zone your server uses.
- Redirect output if you want to keep it: append
>> /var/log/job.log 2>&1. The crontab line builder assembles the whole line.
FAQ
Is "*/30 * * * *" the same on every server?
The five-field form means the same thing in Linux cron, Kubernetes, GitHub Actions and most libraries. The clock it follows differs:
a Linux server uses its own time zone (or CRON_TZ on cronie), GitHub Actions and AWS EventBridge rules use UTC unless a time zone is configured, and Kubernetes uses the controller's zone unless .spec.timeZone is set.
Why do Quartz and AWS need a "?"
Both require exactly one of day-of-month and day-of-week to be ?, meaning "no specific value"; they refuse an expression that restricts both, or leaves both as *.
How do I check it will run when I expect?
The widget above lists the next runs in the time zone you choose, and flags any run that lands in a daylight-saving gap or a repeated hour. For a whole crontab, paste it into the crontab viewer.