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Well, systemd developers made one of the classic blunders a software developer can do: make a program that has to deal with time and dates. Every time I have to deal with timestamps I'm like "oh shit, here we go again".
Anyway, as I understood it the reason this is in systemd is because they wanted to replace cron, and it's fine by me because cron has it's own brain-hurt. (The cron syntax is something that always makes me squint real hard for a while.)
I'm sorry but Cron is really easy, of all systems.
Try using systemd with an ssh server that you want to have running on a non standard port. On non systemd it's a 15 second ordeal while on systemd I don't even know where to start, I pushed it out of my memories. It's something something create files here, restart demons there, removing other files, it is WAY WAY over complicated
What do you mean? You literally just change the /etc/sshd config to point at a different port do you not?
Well cron is "really easy" as long as your requirements are really easy too.
Run a task at specific hour or minute or weekday or whatever? Easy peasy.
Run a task at complex intervals? What the fuck is this syntax. How do I get it right even. Guess I'll come back next week and see if it ran correctly.
Actually have to look at the calendar to schedule this stuff? Oh lawd here come the hacks, they're so wide, they're coming
Run a task at, say, granularity of seconds? Of course it's not supported, who would ever need that, if you really need that just do an evil janky shellscript hack
Yeah and they actually added some usability in the form of that utility helping you debug what you're doing. Pretty nice!
Just write your own initialization system in bash. It is more reliable and less bloated.
This is basically just a way nicer, more flexible cron syntax being dressed up as something ridiculous. There are legitimate reasons for wanting something like this, like running some sort of resource heavy disk optimization the first Friday evening of every month or something.
Systemd ignored my calendar override for the builtin raid scanner, so every week my server would chug to a halt to scan the entire array.
In true systemd fashion, the documentation could not explain this behavior, so I had to make a full copy override instead of a merge override because reasons.
Ahh, you made my day!
Systemd. A tool created in search of problem.
The problem: incomprehensible init scripts
$ systemd-analyze calendar tomorrow
Failed to parse calendar specification 'tomorrow': Invalid argument
Hint: this expression is a valid timestamp. Use 'systemd-analyze timestamp "tomorrow"' instead?
$ systemd-analyze timestamp tuesday
Failed to parse "tuesday": Invalid argument
Hint: this expression is a valid calendar specification. Use 'systemd-analyze calendar "tuesday"' instead?
ಠ_ಠ
$ for day in Mon Tue Wed Thu Fri Sat Sun; do TZ=UTC systemd-analyze calendar "$day 02-29"|tail -2; done
Next elapse: Mon 2044-02-29 00:00:00 UTC
From now: 19 years 4 months left
Next elapse: Tue 2028-02-29 00:00:00 UTC
From now: 3 years 4 months left
Next elapse: Wed 2040-02-29 00:00:00 UTC
From now: 15 years 4 months left
Next elapse: Thu 2052-02-29 00:00:00 UTC
From now: 27 years 4 months left
Next elapse: Fri 2036-02-29 00:00:00 UTC
From now: 11 years 4 months left
Next elapse: Sat 2048-02-29 00:00:00 UTC
From now: 23 years 4 months left
Next elapse: Sun 2032-02-29 00:00:00 UTC
From now: 7 years 4 months left
(It checks out.)
Surprisingly its calendar specification parser actually allows for 31 days in every month:
$ TZ=UTC systemd-analyze calendar '02-29' && echo OK || echo not OK
Original form: 02-29
Normalized form: *-02-29 00:00:00
Next elapse: Tue 2028-02-29 00:00:00 UTC
From now: 3 years 4 months left
OK
$ TZ=UTC systemd-analyze calendar '02-30' && echo OK || echo not OK
Original form: 02-30
Normalized form: *-02-30 00:00:00
Next elapse: never
OK
$ TZ=UTC systemd-analyze calendar '02-31' && echo OK || echo not OK
Original form: 02-31
Normalized form: *-02-31 00:00:00
Next elapse: never
OK
$ TZ=UTC systemd-analyze calendar '02-32' && echo OK || echo not OK
Failed to parse calendar specification '02-32': Invalid argument
not OK
This plays some kind of role in the debate of systemd being good or not. I'm not sure if goes in the good column or the bad column, but I know it goes into a column.
I am typically in the group saying "systemd is overlarge with too many responsibilities" but this capability makes perfect sense for its job running services. Probably the good column.
This kinda functionality is surprisingly apropos to a problem I have a work, I realize. And yet, I have k8s. More and more I am appreciating the niche systemd can play with pets instead of cattle and wished corps weren't jumping to managed k8s and all of that complexity it entails immediately.
You can run systemd (or cron) inside a pod for scheduling and call the kubernetes API from there to run jobs and stuff. Not sure if this helps you, but it can be easy to overlook.
I think it depends which side of the debate one is on?