Re: Q: systemd-timer vs cron

[Michael Biebl <biebl@debian.org>]

Am 12.03.22 um 08:09 schrieb Andreas Metzler:
> On 2022-03-12 Hideki Yamane <henrich@iijmio-mail.jp> wrote:
> >   Is there any suggestion or guideline for pacakges that contain
> >   both systemd-timer unit setting and cronjob? Don't they conflict
> >   or not
>
> Hello,
>
> You want to skip running the cronjob on systems with systemd as init
> systems. e.g. exim's daily cronjob works like this:
> 1. the systemd unit runs /etc/cron.daily/exim4-base with argument
>     systemd-timer.
> 2. /etc/cron.daily/exim4-base checks for a systemd setup by testing
>     existence of /run/systemd/system. On a systemd setup the script
>     exits immediately when executed from cron (i.e. $1!=systemd-timer).

I would consider this an anti-pattern.
If you have such a complex cron-daily script, I'd factor that out into a 
script in /usr/lib/foo and call that directly from both the cron entry 
and the systemd timer.

It's the same kind of anti pattern like creating a .service unit containing
ExecStart=/etc/init.d/foo systemd

Please don't do that.
If you actually have a need to call complex shell machinery to run your 
daemon, please factor this out into an independent script and call it 
from either the sysv init script or the systemd service file.

systemd services should not depend on SysV init scripts and systemd 
timers should not depend on cron files.

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