cron at every 51st minute

cooljai · 02-23-2009, 04:56 AM

Hi,

I want to run a cronjob at every 51st minute (not every hour 51 minute).

for example, if first run is at 1:51, then second run should be at 2:42 (every 51st minute).

Is specifying */51 in minute field do the trick? or there's something else I need to consider?

Please suggest.

acid_kewpie · 02-23-2009, 05:05 AM

No, that's not possible. Cron just periodically checks if any crontab entries match the current time. You'd need to write your own script to loop round or such like.

colucix · 02-23-2009, 05:34 AM

As suggested by acid_kewpie you have to do this by the script itself. For example you can write instructions at the end of the script to update the crontab:

Code:

#!/bin/bash
<your code here>

# -----------------------------------------------------------
#  Update the crontab for the next job
# -----------------------------------------------------------
crontab < <(date -d "51 minutes" +"%M %H %d %m * $0")

Take in mind that the statement above overwrites the content of the crontab. If you have other entries in the actual crontab, they will be deleted. In this case you have to re-write them all from the script itself.

acid_kewpie · 02-23-2009, 05:58 AM

if it's only there to run once, i'd have thought an "at" command would be nicer...?

jlinkels · 02-23-2009, 06:05 AM

I think the at command is suited better here.

Code:

#!/bin/bash
<your code here>

echo /path/to/your/script | at now+51 minutes

Doublecheck the syntax on at, else you will wait very long and see nothing happen.

jlinkels

=== Chris you were faster than I was!

colucix · 02-23-2009, 06:06 AM

I agree. This would overcome the problem of overwriting the whole crontab, too.

cooljai · 02-23-2009, 06:10 AM

Thanks a lot!!

I'll have to take another look at requirement and make some more tweaks

acid_kewpie · 02-23-2009, 06:49 AM

wrong thread. bum.