Re: [gentoo-user] Bug in run-crons?

[Frank Steinmetzger <Warp_7@gmx.de>]

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Am Mon, Dec 13, 2021 at 04:54:30PM -0500 schrieb Rich Freeman:
> On Mon, Dec 13, 2021 at 4:42 PM Michael Orlitzky <mjo@gentoo.org> wrote:
> >
> > On Mon, 2021-12-13 at 22:38 +0100, Frank Steinmetzger wrote:
> > >
> > > Well I *could* disable run-crons altogether and add entries to fcron’s own
> > > crontab which would run those scripts in /etc/cron.{hourly,daily,...}
> > > instead.
> > >
> > > However, I like predictable times at which those jobs will run. Especially
> > > if one of them is a zfs scrub; the NAS is powered down for weeks, sometimes
> > > months. And when I power it up, it’s for a reason. And that reason usually
> > > is not a scrub, which—at the current zfs fill level—takes 10½ hours.
> > >
> >
> > Why choose fcron then? It sounds like you have the same rationale as I
> > do: "no, I don't want to run the 4am backup job in the middle of the
> > business day just because it wasn't run at 4am."

Fair point.
Fcron has a serialisation feature, so that for instance updatedb and mandb
don’t run at the same time. Me kinda liky.

> fcron is perfectly capable of running jobs at either set times or at
> loosely-defined intervals that are compensated for if the machine is
> off.

Indeed, I can say "@monthly * 0 *" to run a monthly job (like the scrub)
only at night. *pondering*

> Systemd timers can also be set that way, and can also have
> limits put on scheduling (daily nominally at 3AM but allowed between
> 11PM and 5AM or whatever).  Obviously the more expressive the crontab
> equivalent is, the more you can tweak it to do what you want it to.

I’ve gotten used to systemd on my Arch-based desktops. But the NAS is still
on good-ol’ openrc. :)

> I'll also note that zfs scrubs checkpoint at shutdown and will
> auto-resume where you leave off.

That’s a nice bit of knowledge.

> If they are involved multiple times
> with the default options I think any attempt to scrub something that
> is already being scrubbed is just a no-op.  Obviously if you don't
> want all that IO during the day you'll have to do something more
> clever - you can instruct it to pause and resume so you could have a
> couple of crontab entries and scripts to do just that.

Or, since I am the only user of that system, I could go back to my previous
way: just run the scrub manually every other month or so before I go to bed.
Because then I know that nothing will interfere with it and it won’t
interfere with anything else.

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