Shell Programming and Scripting

In your given Crontab Entry:

Code:

05 00 * * 0,4,5,6, sleep 45 && /usr/local/bin/set_radio_cron grp0 0 0 & 

I can see there is & and one extra comma marked red there.

In above the sleep command is not working but the other command "/usr/local/bin/set_radio_cron grp0 0 0" is working for only below condition.
-> when present time is hr 00:05:12 sec , given time hr 00:05:00 sec

The above quoted command is working fine when :
-->when present time is hr 00:04:12 sec , given time hr 00:05:00 sec

please comment on above ...

If I understand this discussion properly, you are creating a crontab "on the fly", perhaps just one minute before it is timed to run? Why?

Crontabs are normally set up and left alone. The crontabs are read into memory when the kernel boots and the last modified date/time of the crontab is also remembered. "Periodically" the cron daemon will inspect the crontabs to see if anything has changed (by looking at the last modified date/time) and if it has, it will reload that table. Therefore, to my mind, there is no guarantee that a crontab created one minute before it is due to run will be executed one minute later. The cron daemon might not have seen the change by then.

Can any other forum members confirm what I've just said please.

@manoj424
The cron fires at 05:00 exactly, precisely, and to the millisecond.
Any change you make after that time is too late.
Get it?


I agree that you should also give cron a minute or more to see the change. This varies from system to system. The benchmark would be the second the "crontab -e" command finishes.
There is no way that a change made after 05:00 to a cron scheduled at 05:00 would be actioned until the following day.