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Tasklist

FS#27675 - [dcron] If a job is scheduled to run within a band of times with a FREQ setting, and if the job

Attached to Project: Community Packages
Opened by Nick Coleman (NickC) - Thursday, 22 December 2011, 23:02 GMT
Last edited by Evangelos Foutras (foutrelis) - Thursday, 17 January 2013, 01:26 GMT
Task Type Bug Report
Category Packages
Status Closed
Assigned To No-one
Architecture All
Severity Low
Priority Normal
Reported Version
Due in Version Undecided
Due Date Undecided
Percent Complete 100%
Votes 0
Private No

Details

Description:

If a job is scheduled to run within a band of times with a FREQ setting, and if the job (for whatever reason) is run towards the end of the band, it will never run again at an earlier time.

An example is probably better:

I have a job I want to run once a day early in the morning. To cater for the situation when my laptop is closed (i.e. in sleep mode), I set up the crontab like this:

* 7-10 * * * FREQ=1d myjob

If I open my laptop at 9am, all subsequent runs will never be before 9am due to the FREQ=1d. This means the job could eventually ending up always running at the max(time of all previous runs).

The simple solution is to specify FREQ=12h, but perhaps this is not obvious to a casual user of cron. I suspect they would naively specify FREQ=1d because they want it to run every day. Makes sense, right? Well, no, that is not how it works.

I read the code and it is not a simple fix (due to the many corner cases one can think of) and you have to ask yourself if it is worth it.

Probably the easiest fix is to add a note to crontab.1 in the section where FREQ is described, something like:

"Note that if a job runs successfully at the latest possible time, you should specify a FREQ low enough that it can next run at the earliest possible time. The naive setting of 1d for every day may not be best."

I go into more detail in a blog post at
<http://www.nickcoleman.org/blog/index.cgi?post=cronslackware%21201112181115%21unix>


Version 4.5
This task depends upon

Closed by  Evangelos Foutras (foutrelis)
Thursday, 17 January 2013, 01:26 GMT
Reason for closing:  No response
Comment by Nick Coleman (NickC) - Thursday, 22 December 2011, 23:15 GMT
Can a mod edit this to add a Summary.
Comment by Greg (dolby) - Monday, 19 November 2012, 07:01 GMT
Please report upstream maybe suggesting to improve documentation about this.

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