Re: Crontab | random execution time

On 07/03/2022 14:14, Steve O'Hara-Smith wrote:
> On Mon, 7 Mar 2022 14:36:19 +0100
> Jos Chrispijn <bsduser@cloudzeeland.nl> wrote:
> 
>> Dear list,
>> I am trying to run a cron job, starting once every two hours and at 
>> random minute  in the half our of that cron scheme:
>>
>> SHELL=/bin/sh
>> PATH=/etc:/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:/usr/local/etc
>> 0~30   */2     *       *       *       root /root/cronjobs/run_myjob
>>
>> Unfortunately it is running exactly on the hour instead of random 
>> between 0-30 minutes.
> 
> 	I'd expect that to run once a minute for the first thirty minutes
> of even numbered hours.
> 
> 	The usual way to achieve what you want is to add a random sleep in
> front of the job, or just rely on cron's jitter feature which isn't usually
> set for that much spread and affects every job.
> 

That line has a '~' in it which isn't a documented form. I suspect cron
 reads it as '0'.

To do a random sleep of 0-30 minutes add

	sleep `jot -r 1 0 1800`

to the start of your command.

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