I believe one of the major distro lines (redhat or debian, I forget which) uses systemd-cron, where cron is just a thin wrapper around systemd. You get more power from writing the unit files directly, but if all you ever need is a simple cron job, you have the old interface still available.
Love systemd timers
81–90 of 309 posts
Re: Love systemd timers
#82Timers can work with arbitrary units (not just a similarly-named service unit) so they can be surprisingly flexible. I have a timer on my servers that starts a backup.target that fires off a full "restic backup","restic prune", "restic forget" backup cycle each morning with randomized start times and notifications. The actual restic-* units are Podman Quadlets so the whole setup runs agnosticaly of what's on the serv…
I feel like systemd units could need a layer of abstraction above them, so instead of editing the files manually, a tool would do it, some kind of declarative CLI or something. Probably not really a concern in the age of LLMs anymore, but it feels just slightly too tedious every time.
Re: Love systemd timers
#83I'm fully ready to drink the "just let systemd do all the things" kool-aid, but I would love to see some sort of introductory/tutorial info into some of the things it can do other than services - i.e. containers and timers. I know man pages exist, but it would be nice if there was more scannable intro out there.
Re: Love systemd timers
#84I haven't used systemd timers enough to disagree, but > Ambiguous $PATH settings make cron script execution difficult to predict. What makes you say that? You can set the PATH right in the crontab. Is that harder to "predict" than it being set in /etc/bashrc, ~/.bashrc, ~/.profile, ~/.bash_profile, /etc/systemd/…, or wherever else? > You might feel cool knowing the scheduling grammar by heart I've used Linux since 19…
Having had to work on an application supposedly supporting cron expressions: the numbers are just the basic parts of the language.
When someone inputs something ridiculous like "5,3/4 4-8,11 1 4,5,6,9-11 */2" you get to enjoy the fun of reverse engineering what they meant (it's never what they actually wrote).
And that's before you get to all the extensions supported in some cron environments (but not all).
I find systemd timers a lot more manageable. Things like having control over whether or not long-running jobs are allowed to overlap and the ability to run tasks between start-finish rather than a fixed time window are major improvements for me. At some point my VPS went down because the backup job ran into some kind of symlink loop and cron just kept spawning more and more backup tasks even though none of them finished.
Having to re-write commands and scripts because CRON had its own special PATH was also a pain point, but the same can be true for some types of systemd timers. But: you can execute those timers manually if you want instead of updating the crontab to trigger in 30 seconds and simply waiting.
Re: Love systemd timers
#85I'm fully ready to drink the "just let systemd do all the things" kool-aid, but I would love to see some sort of introductory/tutorial info into some of the things it can do other than services - i.e. containers and timers. I know man pages exist, but it would be nice if there was more scannable intro out there.
btw that xz hack only effect systemd distros
Re: Love systemd timers
#86There's another big feature: You're not relying on the time zone to which the server was set (like with cron) but can explicitly specify a time zone: https://www.freedesktop.org/software/systemd/man/latest/syst...
Of course you can do this trivially in cron as well. It is what the CRON_TZ variable is for.
Re: Love systemd timers
#87Earlier quoted context omitted.
> fallback to running when the system comes online. That isn't something I'd want to happen, it sounds like it creates a potential queue of scripts that will flood the system on start, if it works the way you described. I prefer the deterministic behavior of cron, the script will run when it is specified to run, as you said earlier, as long as the system is running; and as I stated in a separate comment, it will run…
> That isn't something I'd want to happen, it sounds like it creates a potential queue of scripts that will flood the system on start, if it works the way you described. This isn't what happens. If you leave it offline for days it'll only trigger the service only a single time.
I interpreted it more like "I have these 500 different cronjobs all spread out across $unit_of_time. If the system is down for longer than $unit_of_time and then comes back, does all 500 jobs start running instantly (since they missed their previous deadline)?"
Re: Love systemd timers
#88I haven't used systemd timers enough to disagree, but > Ambiguous $PATH settings make cron script execution difficult to predict. What makes you say that? You can set the PATH right in the crontab. Is that harder to "predict" than it being set in /etc/bashrc, ~/.bashrc, ~/.profile, ~/.bash_profile, /etc/systemd/…, or wherever else? > You might feel cool knowing the scheduling grammar by heart I've used Linux since 19…
Having had to work on an application supposedly supporting cron expressions: the numbers are just the basic parts of the language. When someone inputs something ridiculous like "5,3/4 4-8,11 1 4,5,6,9-11 */2" you get to enjoy the fun of reverse engineering what they meant (it's never what they actually wrote). And that's before you get to all the extensions supported in some cron environments (but not all). I find sy…
> 5,3/4 4-8,11 1 4,5,6,9-11 */2
What's so hard about "At 5 minutes past the hour and every 4 minutes, starting at 3 minutes past the hour, at 04:00 AM through 08:59 AM and 11:00 AM, on day 1 of the month, every 2 days of the week, only in April, May, June, and September through November"?
(I used https://crontab.cronhub.io/ to decode it, to be fair)
Re: Love systemd timers
#89There's another big feature: You're not relying on the time zone to which the server was set (like with cron) but can explicitly specify a time zone: https://www.freedesktop.org/software/systemd/man/latest/syst...
Of course you can do this trivially in cron as well. It is what the CRON_TZ variable is for.
This is a GNU extension so not portable.
Re: Love systemd timers
#90Earlier quoted context omitted.
> fallback to running when the system comes online. That isn't something I'd want to happen, it sounds like it creates a potential queue of scripts that will flood the system on start, if it works the way you described. I prefer the deterministic behavior of cron, the script will run when it is specified to run, as you said earlier, as long as the system is running; and as I stated in a separate comment, it will run…
> That isn't something I'd want to happen, it sounds like it creates a potential queue of scripts that will flood the system on start, if it works the way you described. This isn't what happens. If you leave it offline for days it'll only trigger the service only a single time.
If you have 100 different jobs that were supposed to run over the past week, but didn't because offline, when you restart, they they all flood the system on start.
100 jobs all running at different times throughout the week is a very different load than them all falling back and running at the same time on system boot.