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Cron every minute

The cron expression for every minute is * * * * *, five asterisks. How it runs, how to limit it to certain hours or days, and where GitHub Actions and AWS differ.

Cron expression
* * * * *
See the next run times

The expression

* * * * *

Runs once at the start of every minute, around the clock: 60 times an hour, 1,440 times a day. Cron wakes up once a minute, checks every entry, and starts the ones that match, so this is the most frequent schedule standard cron can express.

Field Value Meaning
Minute * every minute, 0-59
Hour * every hour, 0-23
Day of month * every day
Month * every month
Day of week * every day of the week

A * means "any value". With all five fields set to *, nothing narrows the schedule, so the job starts whenever the minute changes (12:00:00, 12:01:00 …), usually within a second of the boundary.

Variants

Schedule Expression
Every minute from 9:00 to 16:59 * 9-16 * * *
Every minute, weekdays only * * * * 1-5
Every minute during the 2 a.m. hour only * 2 * * *
Every 2 minutes */2 * * * *
Every 5 minutes */5 * * * *
Every 30 seconds (needs a workaround) two entries with sleep 30

*/1 * * * * is the same as * * * * *; the step adds nothing.

Where to write it

  • crontab (Linux, macOS): * * * * * /usr/local/bin/poll.sh in crontab -e. Times follow the server's time zone, which only matters once you restrict the hour or day fields.
  • GitHub Actions: the shortest interval GitHub runs is 5 minutes, so * * * * * will not fire every minute there. Schedules are in UTC and can be delayed when runners are busy. Use an external scheduler or a long-running worker instead.
  • Kubernetes CronJob: schedule: "* * * * *" works, but each run starts a new pod. Set concurrencyPolicy: Forbid and keep successfulJobsHistoryLimit low so finished Jobs don't pile up.
  • AWS EventBridge: six fields with ? in one day field: cron(* * * * ? *), or simply rate(1 minute), the smallest rate allowed.

Common mistakes

  • * 9 * * * is not "9 a.m. once". A * in the minute field makes it run 60 times, from 9:00 to 9:59. For once at 9:00 write 0 9 * * *.
  • Overlapping runs. A job that sometimes takes longer than a minute will run in parallel with itself. Wrap it in flock -n /tmp/poll.lock command so a new run exits while the old one is still going.
  • Log and mail floods. Any output is mailed to the crontab owner, 1,440 times a day. Redirect it: command >> /var/log/poll.log 2>&1, and rotate that log.
  • Using cron as a queue. If you need something within seconds of an event, a long-running worker or a message queue reacts faster and costs less than polling every minute.

Paste any expression into the Cron Expression Parser to see it in words and its next run times.