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Systemd.timer, an Alternative to Cron

andrewpillar.com

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Re: Systemd.timer, an Alternative to Cron

#11

Post by phpisthebest »

traverseda wrote: post #3

https://htmx.org/essays/locality-of-behaviour/ Locality of behavior is important. Note how this systemd-thingy is split into two separate files? It's like that a lot in systemd, whoever is doing the architecture doesn't seem to understand why locality of behavior would be desirable, instead taking the IDE approach of writing a bunch of tools to make managing the increased complexity more manageable. Don't glance at a…

>>Locality of behavior is important.

Even your own link talks about the Subjectivity of that opinion, and how LoB is often in conflict with DRY and SoC, both of which I support far more than LoB.

In this context systemd favors Separation of Concerns, the the service is what is being run, and the timer is when is it being run...

it is not that the devs do not "seem to understand why locality of behavior would be desirable" it is they disagree that is more desirable than having a logical separation of concerns...

To me I prefer greater separation of concern than locality

Re: Systemd.timer, an Alternative to Cron

#12

Post by bigpeopleareold »

sparker72678 wrote: post #7

You can pry my crontab out of my cold, dead hands. Seriously, though, cron has been so utterly reliable for me for so many decades now, it will be really hard for me to ever give it up.

I seemed to never care until they took my sysvinit away (or maybe any decent init system :D). Then they took resolv.conf control away. Then when I shutdown my computer, some random process takes 1 min 30 seconds to shutdown when it probably doesn't need to. Then I read on hacker news recently that Fedora uses a systemd daemon for handling OOM and the writer said it was terribly misconfigured particularly when it shutdown his X session and all processes related to it when an OOM condition happened. I am not a Linux admin (or at least a sophisticated one so I can look smart with systemd), but now they are taking cron away too? :D

I kid about this, in a way, and I know I should accept the inevitable, but I feel like just moving to Devuan on my laptop and use a nice init system, like OpenRC :D

Re: Systemd.timer, an Alternative to Cron

#13

Post by pm90 »

I've had the opportunity to delve into systemd in a previous role.

This sounds a bit weird, but its not easy to get started with, unless you're used to reading man pages. But once you're able to read man pages, all of systemd behavior is documented in the man pages. I do wish there were more human friendly docs though, especially for younger engineers used to better sorts of docs.

Anyways, once you do get the hang of it, its an immensely powerful system, but like any such system it has its quirks and edge cases. You can get 99% of what you need with it though, and for low level tasks on machines, its pretty amazing.

Re: Systemd.timer, an Alternative to Cron

#14

Post by bravetraveler »

traverseda wrote: post #3

https://htmx.org/essays/locality-of-behaviour/ Locality of behavior is important. Note how this systemd-thingy is split into two separate files? It's like that a lot in systemd, whoever is doing the architecture doesn't seem to understand why locality of behavior would be desirable, instead taking the IDE approach of writing a bunch of tools to make managing the increased complexity more manageable. Don't glance at a…

I think timers handle this fine -- one part sets up the work (service), the other sets up the scheduling of the job (timer)

Speaking of behavior, let's look at cron.

Consider every time you've written one. There's a good chance that it failed for some time because you forgot PATH is make believe there

Or logging. How many times has rotation been rewritten (and broken)?

Without digging through logs that may or may not exist, can you tell me when it last ran successfully?

I can with timers, 'for free'

Re: Systemd.timer, an Alternative to Cron

#15

Post by pikrzyszto »

ghostpepper wrote: post #5
traverseda wrote: post #3

https://htmx.org/essays/locality-of-behaviour/ Locality of behavior is important. Note how this systemd-thingy is split into two separate files? It's like that a lot in systemd, whoever is doing the architecture doesn't seem to understand why locality of behavior would be desirable, instead taking the IDE approach of writing a bunch of tools to make managing the increased complexity more manageable. Don't glance at a…

Binary log files is another example of something that could have advantages in theory but never seems to work well in practice. What used to be "tail /var/log/nginx.log" is now man journalctl journalctl -u nginx journalctl | grep nginx go back to man page to look for more options to search etc

"tail /var/log/nginx.log" is now "journalctl -fu nginx" or "jouranlctl -eu nginx". Not that much of a difference, it really depends what you grow up with. We could argue "tail" is ugly because you never know if it's "tail /var/log/nginx.log" or "tail /var/log/nginx/nginx.log".

A nice feature is that journald gives you flags like "--boot" to see logs only emitted during a specific boot, or "--since '5m ago'" which is not that straightforward to do with the approach you favor. (if there is a way to do it easily, please let me know!)

Re: Systemd.timer, an Alternative to Cron

#16

Post by traverseda »

phpisthebest wrote: post #11
traverseda wrote: post #3

https://htmx.org/essays/locality-of-behaviour/ Locality of behavior is important. Note how this systemd-thingy is split into two separate files? It's like that a lot in systemd, whoever is doing the architecture doesn't seem to understand why locality of behavior would be desirable, instead taking the IDE approach of writing a bunch of tools to make managing the increased complexity more manageable. Don't glance at a…

>>Locality of behavior is important. Even your own link talks about the Subjectivity of that opinion, and how LoB is often in conflict with DRY and SoC, both of which I support far more than LoB. In this context systemd favors Separation of Concerns, the the service is what is being run, and the timer is when is it being run... it is not that the devs do not "seem to understand why locality of behavior would be desir…

I think that's probably a trade off that large enterprises often make. It tends to work well for very large teams, and especially if you're trying to make your tech team fungible. Still, there's such a thing as taking it too far.

I think there's a middle ground. Sure, a single crontab makes it hard for packages to schedule things and makes it hard to assign ownership to individual packages/people/whatever. I can recognize that, and how it would be a problem for a large enterprise or even just for software developers who want to bundle some kind of cronjob with their package.

What you could do instead of a crontab is have one folder with a bunch of services/timers in it, where each file represents a single service that needs to be run. It would mean that you can still understand all of what's going on timer wise by looking carefully at one source, but you can still assign different services/timers to different people/packages/organizational-units/whatever.

Splitting each individual cronjobs into 2 different files is just crazy from where I am. Like you already have a bunch of different service types, at least give us the option to use a "periodic-oneshot" service type instead of this craziness. There's no need to have different packages/people responsible for a service and its timer, and if there is some edge case where it is you can still have ssperate timer services just they can live in a separate periodic-oneshot service file and use the original service as a dependency.

There's separation of concerns and then there's this. Take any principle too far and you get some craziness, and systemd has most of the infrastructure needed to solve this in a much more elegant way. Like at some point it has to just be bad design and not just different priorities, right?

Re: Systemd.timer, an Alternative to Cron

#18

Post by candiddevmike »

pikrzyszto wrote: post #15
ghostpepper wrote: post #5

Earlier quoted context omitted.

Binary log files is another example of something that could have advantages in theory but never seems to work well in practice. What used to be "tail /var/log/nginx.log" is now man journalctl journalctl -u nginx journalctl | grep nginx go back to man page to look for more options to search etc

"tail /var/log/nginx.log" is now "journalctl -fu nginx" or "jouranlctl -eu nginx". Not that much of a difference, it really depends what you grow up with. We could argue "tail" is ugly because you never know if it's "tail /var/log/nginx.log" or "tail /var/log/nginx/nginx.log". A nice feature is that journald gives you flags like "--boot" to see logs only emitted during a specific boot, or "--since '5m ago'" which is…

I personally find journalctl -fu $service very cathartic, because I'm almost always typing this command when $service isn't working.

Re: Systemd.timer, an Alternative to Cron

#19

Post by lazide »

traverseda wrote: post #3

https://htmx.org/essays/locality-of-behaviour/ Locality of behavior is important. Note how this systemd-thingy is split into two separate files? It's like that a lot in systemd, whoever is doing the architecture doesn't seem to understand why locality of behavior would be desirable, instead taking the IDE approach of writing a bunch of tools to make managing the increased complexity more manageable. Don't glance at a…

Well, except for /etc/crontab, /etc/corn.daily|weekly|whatever, /var/spool/crontabs, etc.

Re: Systemd.timer, an Alternative to Cron

#20

Post by Hikikomori »

ghostpepper wrote: post #5
traverseda wrote: post #3

https://htmx.org/essays/locality-of-behaviour/ Locality of behavior is important. Note how this systemd-thingy is split into two separate files? It's like that a lot in systemd, whoever is doing the architecture doesn't seem to understand why locality of behavior would be desirable, instead taking the IDE approach of writing a bunch of tools to make managing the increased complexity more manageable. Don't glance at a…

Binary log files is another example of something that could have advantages in theory but never seems to work well in practice. What used to be "tail /var/log/nginx.log" is now man journalctl journalctl -u nginx journalctl | grep nginx go back to man page to look for more options to search etc

Can still do that?
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