Replacing Cron/Anacron/Atd

[Evan]

On Tue, Aug 31, 2010 at 5:00 PM, Evan <eapache at gmail.com> wrote:
> Hi all.
>
> I've been following upstart development with half an eye for a while
> now, and one of the features that has always interested me the most is
> the plans for it to eventually replace cron/anacron/atd as the
> system-wide task scheduling tool. I don't think there are pre-existing
> designs for this beyond what's listed on the FAQ (if there are, I
> couldn't find them with Google), so I gave it some thought myself.
> Here are a few options I came up with:
>
> My initial thought was to simply have upstart emit standard events
> every fixed period of time that jobs could hook into (ie 'starts on
> hourly'). However this runs into problems fairly quickly: it's not
> very flexible, it would be fairly complicated to add
> anacron-capabilities to it, and writing a job to start every x hours
> (x > 1) would require some uglyness in a pre-start script.  While this
> would certainly work, it isn't great.
>
> My next thought was to have a config file somewhere
> (/etc/init-schedule.conf ?) where users could configure custom timed
> events. Upstart would read it, and know to emit event X every Tuesday,
> event Y every 3 hours, and event Z once a day. While this would be
> significantly cleaner than the previous solution, it still has one
> problem which I dislike - configuration for time-based jobs ends up in
> two different files. If I have job B that has a 'starts on
> B-schedule', the user then has to search through init-schedule
> separately to figure out when B-schedule is actually emitted. A better
> solution, but again not optimal.
>
> My third and final design is in many ways the farthest from the
> original 'everything by events' design of upstart, but I believe it
> most effectively replaces the existing cron/anacron/atd system.
> Upstart will designate a special event (like 'startup' is today)
> called 'schedule'. This event will have one parameter called 'job'. If
> schedule is referenced in a start or stop stanza without a specified
> job parameter, job=$self will be assumed for convenience. Each job
> file will have optional 'schedule' stanzas, similar in syntax to atd.
> Upstart will parse these stanzas, and when appropriate will emit a
> 'schedule job=x' event. For the user, anacron-like functionality will
> be available via the special-case schedule stanza 'schedule if
> missed', and atd-like functionality will be available via 'initctl
> schedule'.
>
> There follows a very simple upstart job using this proposed syntax:
> #####
> start on schedule
>
> schedule every hour
> schedule if missed
>
> task
>
> console output
> exec echo "This job runs like an hourly anacron job!"
> #####
>
> Of course these are only proposals - I'm not very familiar with the
> innards of upstart, so I'm sure I've made some false assumptions.
> However, I hope these will serve as starting-points for a proper
> design discussion. I'm quite familiar with C, and I've been looking
> for a place to give back to Ubuntu for a while now. If a design is
> decided upon for this feature, I'd be willing to spend some time
> implementing it.
>
> Thanks,
> Evan Huus

Does nobody else have any thoughts on this feature or
did I just bring it up at a busy time in the development cycle?

Evan