Run a Cron Job Every 4 Minutes
To run a job every 4 minutes, use */4 * * * *. It fires at minute 0, 4, 8, 12 ... within each hour.
The expression
*/4 * * * * runs at minute 0, 4, 8, 12, 16 ... 56, then repeats each hour.
The interval resets each hour
Because 4 divides 60 evenly, the gap between the last run (56) and the top of the next hour (0) is also 4 minutes, so the cadence is perfectly even. Intervals that don't divide 60 (like */7) jump at the hour boundary.
Sub-minute is not possible
Cron's finest granularity is one minute. For "every 30 seconds" you need a loop with sleep, not cron alone.
FAQ
What is the cron expression for every 4 minutes?
*/4 * * * * runs every 4 minutes (minute 0, 4, 8, ... 56 of each hour).
Is the 4-minute gap even across the hour?
Yes. 4 divides 60 evenly, so the interval stays exactly 4 minutes even across the top-of-hour boundary.
Can cron run more often than once a minute?
No. Cron's smallest unit is one minute; for sub-minute schedules use a shell loop with sleep or a dedicated scheduler.