Running a cron job on Linux every six hours

Question

How can I run command every six hours every day?

I tried the following, but it did not work:

/6 * * * * *  mycommand

possible duplicate of [How to run crontab for every 2 hours](http://stackoverflow.com/questions/6423532/how-to-run-crontab-for-every-2-hours) — Cas, Sep 20 '14 at 11:23

score 341 · Accepted Answer · edited Jun 14 '20 at 16:31

341

You forgot a *, and you've too many fields. It's the hour you need to care about

0 */6 * * * /path/to/mycommand

This means every sixth hour starting from 0, i.e. at hour 0, 6, 12 and 18 which you could write as

0 0,6,12,18 * * * /path/to/mycommand

edited Jun 14 '20 at 16:31

Peter Mortensen

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answered Jul 19 '12 at 14:18

nos

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thank your for the response, this is every 6 hours starting what time? the time when the cron is created? – Gandalf StormCrow Jul 19 '12 at 14:19
thanks, so if I wanted to run it starting from 15:00 every 6 hours it would be `15 15,23,05,11 * * * /path/to/mycommand` ? – Gandalf StormCrow Jul 19 '12 at 14:26
6

Yes, though the first field is the minute, which you've set to 15, so that'll mean 15:15,23:15,05:15 and 11:15. (which isn't every 6th hour btw, you might have meant `0 15,21,3,9 * * *`) – nos Jul 19 '12 at 14:31

score 7 · Answer 2 · answered Jul 19 '12 at 14:19

7

You should include a path to your command, since cron runs with an extensively cut-down environment. You won't have all the environment variables you have in your interactive shell session.

It's a good idea to specify an absolute path to your script/binary, or define PATH in the crontab itself. To help debug any issues I would also redirect stdout/err to a log file.

answered Jul 19 '12 at 14:19

Brian Agnew

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thanks for the response, but if I declare environment variables inside my sh file like `export variable=something` I get to still use them inside that same script? and I use date command alot inside the script – Gandalf StormCrow Jul 19 '12 at 14:36
@Gandalf - Yes. You can define all your env variables inside the script. That's a good idea since it means your script is standalone and isolated from other stuff you may want to run within cron – Brian Agnew Jul 19 '12 at 16:01

score 5 · Answer 3 · edited Jun 14 '20 at 16:31

5

0 */6 * * * command

This will be the perfect way to say 6 hours a day.

Your command puts in for six minutes!

edited Jun 14 '20 at 16:31

Peter Mortensen

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answered Sep 08 '16 at 07:35

rkoots

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@ArsenArsen I am pretty sure it was because it doesn't really add anything to the existing accepted answer, wrote 4 years before it. – Adinia Apr 03 '17 at 09:31

score 5 · Answer 4 · edited Jun 14 '20 at 16:34

5

Please keep attention at this syntax:

* */6 * * *

This means 60 times (every minute) every 6 hours,

not

one time every 6 hours.

edited Jun 14 '20 at 16:34

Peter Mortensen

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answered Apr 10 '20 at 12:54

Andrea Bisello

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score 0 · Answer 5 · edited Sep 03 '18 at 17:28

0

0 */6 * * *

crontab every 6 hours is a commonly used cron schedule.

edited Sep 03 '18 at 17:28

halfer

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answered Feb 01 '18 at 08:33

Nilesh Patil

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What does this answer add that the other answers don't? @rkoots has already mentioned this exact command. – Blue Feb 01 '18 at 08:43
*"Commonly used"*? Why? Can you elaborate? – Peter Mortensen Jun 14 '20 at 16:33

score 0 · Answer 6 · answered Dec 18 '22 at 16:29

0

nice website for this purpose :)

https://cron.help/

answered Dec 18 '22 at 16:29

Hamid Zandi

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score -3 · Answer 7 · edited Sep 03 '18 at 17:29

-3

Try:

0 */6 * * * command

. * has to

edited Sep 03 '18 at 17:29

halfer

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answered Jun 25 '18 at 10:53

rkoots

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The last line here doesn't make much sense. Would you consider expanding it? – halfer Sep 03 '18 at 17:29
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looks like the answer is incomplete – ajayramesh Jan 20 '19 at 03:57

Running a cron job on Linux every six hours

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