How the command "at" works?

[Peng Yu]

On Friday, August 5, 2016, Karl Auer <kauer at biplane.com.au> wrote:

> On Fri, 2016-08-05 at 20:27 -0500, Peng Yu wrote:
> > I am asking how "at" works internally not how to use it. It seems man
> > does not help much for this purpose.
>
> If you read the "at" man page it says you should "see also" atd, and
> that answers pretty much all your questions.
>
> "at" is actually two parts - the user interface "at" and a daemon
> "atd".
>
> They communicate through job files: "at" puts jobs in a directory
> (/var/spool/cron/atjobs), "atd" reads them out of there and runs them.
>
> Each job file is an ordinary shell script (sh not bash!).


Thanks for the information. I actually want to make a customized job
scheduler so that it will be able to run bash fuction defined in the
environment of the bash shell in which the job scheduler is called.

The thing that at* commands do can be done in a scripting language which
will make code easier to decipher than in C.

Do you know any alternative job scheduler to 'at' with the same fuction but
written in a scripting language?

It's mostly
> commands to set the environment and change to the right directory; the
> last lines are whatever you typed into "at".
>
> You can find out more about atd through "man atd" and "systemctl status
> atd". You might also want to check out at.allow and at.deny.
>
> Interestingly, atd is started with the -f option, which is supposed to
> run it in the foreground. Odd. It's definitely not in the foreground.
>
> Regards, K.
>
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-- 
Regards,
Peng
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