Question 1

How do you run a cron job every minute only on specific hours?

Accepted Answer

Use `* 11,16,21 * * * command`. The minute `*` means every minute, the hour list `11,16,21` restricts it to those three hours — 180 runs per day. To reduce volume, use `*/5`, `*/15` or `0` in the minute field. To restrict to weekdays, add `1-5` in the day-of-week field.

Question 2

How do I set up a cron job that runs every day at 1PM, 2PM and 3PM?

Accepted Answer

Use a comma list in the hour field: `0 13,14,15 * * * command` runs at 13:00, 14:00 and 15:00. For consecutive hours, the equivalent range form is `0 13-15 * * *`. Non-consecutive times only work with the list form: `0 13,16,21 * * *`. If minutes differ per hour, use separate cron lines.

Question 3

How can I run command every six hours every day?

Accepted Answer

Use `0 */6 * * * command`. It fires four times a day at 00:00, 06:00, 12:00 and 18:00. The minute is `0` (top of the hour) and the hour step `*/6` selects every sixth hour. To shift the start, use a range: `0 3-23/6 * * *` fires at 03/09/15/21.

Question 4

I am trying to add a crontab entry to execute a script every 30 minutes, on the hour and 30 minutes past the hour or something similar. How can I do this?

Accepted Answer

Use `30 * * * * command` to run at half past every hour, or `0,30 * * * * command` (equivalently `*/30 * * * *`) to run on the hour and at 30 past. Cron matches a schedule, not an interval — the actual time between runs depends on which clock minutes match the expression.

How do you run a cron job every minute only on specific hours?

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April 2026

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