For testing purposes ,I would like to run a command check every 15 minutes past the hour. I'm a little bit confused about the correct timeframe syntax of the crontab :

Is this correct :

*/15 * * * * 


this one :

15 * * * *

I think its the first one ,since the second will run 15 minutes (once) after 1 hour passed. Any ideas?


The first one will (with most common cron implementations) run the command every 15 minutes and is equivalent to 0,15,30,45 * * * *.

The second one will run 15 minutes past the hour, every hour.

This is described in the crontab(5) manual on your system (man 5 crontab).

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  • @VorX I think I slightly misread your question and have amended the answer... I hope that it's still clear. – Kusalananda Jan 30 '18 at 9:17

Your first crontab line means running a command every 15 minutes.

The second one means running a command 15 minutes after every hour.

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The first one will execute at every 15th minute, that is xxh15; xxh30; xxh45; (xx + 1)h00.

The second one will execute at minute 15. Ex: xxh15; (xx + 1)h15; (xx + 2)h15.

If you have any doubts in how to set a crontab I recommed you to check the crontab guru.

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This one is correct

*/15 * * * * 

Also, check the crontab.guru website.

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  • It depends on how you interpret "every 15 minutes past the hour" in the question. It's either "every 15 minutes" or "15 minutes past every hour". – Kusalananda Jan 30 '18 at 13:31

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