| ▲ | eqvinox 2 hours ago |
| How do you express those things in a systemd timer? E.g. run something 4x per day, */6 in cron. |
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| ▲ | iam-TJ an hour ago | parent | next [-] |
| $ systemctl cat public-inbox-watch@.timer
# /etc/systemd/system/public-inbox-watch@.timer
[Unit]
Description=Periodic fetch of public mailing list
[Timer]
# twice a day
OnCalendar=*-*-* 5,17:35
RandomizedDelaySec=1h
Persistent=true
[Install]
WantedBy=multi-user.target
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| ▲ | ecnahc515 an hour ago | parent | prev | next [-] |
| Something like: OnCalendar=00/6
You can test it with: systemd-analyze calendar --iterations=6 '0/6:00:00'
The format is `DayOfWeek Year-Month-Day Hour:Minute:Second`https://www.freedesktop.org/software/systemd/man/latest/syst... |
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| ▲ | PunchyHamster an hour ago | parent | prev | next [-] |
| That's simple but consider "run something 4x per day but randomize a delay by hour so all of the 200 servers doing that task won't run it all at once" In cron, you basically have to either use your configuration management to generate those times, or have a random delay script running before the command In systemd timers, it's just OnCalendar=0/6:00:00
RandomizedOffsetSec=60m
and the offset generated will be stable for the job on a given machine (i.e. always same on this machine but different on others) so you will get nice uniform distribution of load.If you add Persist=true
the job will also be run once if there was one or more scheduled runs when the machine was down |
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| ▲ | simoncion 44 minutes ago | parent [-] | | > In cron, you basically have to either use your configuration management to generate those times, or have a random delay script running before the command Nope. From crontab(5) The RANDOM_DELAY variable allows delaying job startups by random amount
of minutes with upper limit specified by the variable. The random scal‐
ing factor is determined during the cron daemon startup so it remains
constant for the whole run time of the daemon.
That's from my cronie install, but it looks like this has been a feature of some crons for at least a decade. (Notice that the post date of [0] is in 2016.) Given that cronie is based on vixie-cron, and I think I was was using vixie-cron in 2002, I bet it's been a thing for at least twenty years.[0] <https://stackoverflow.com/a/34815984> |
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| ▲ | simoncion an hour ago | parent | prev [-] |
| Sure, I'll pile on here. To do nontrivial scheduling you'd use the entirely-obvious-and-intuitive syntax described at [0]. For example: Mon,Fri *-01/2-01,03 *:30:45
Who'd ever want to go back crontab format for nontrivial scheduling? [1][0] <https://www.freedesktop.org/software/systemd/man/latest/syst...> [1] This question is sarcasm. SystemD is often like this... dead simple things look dead simple, but complex things are -if they're possible at all- at least as complex as they are everywhere else. |
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| ▲ | p0358 31 minutes ago | parent [-] | | If you know the syntax, it's still actually rather trivial. Still easier to read than advanced cron magic. | | |
| ▲ | simoncion 22 minutes ago | parent [-] | | > Still easier to read than advanced cron magic. Looking at the other examples on that page, I'm gonna say that it's only arguably easier to read for basic stuff... especially if you're familiar with the syntax. The complex stuff is -at best- just as difficult. |
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