On Sun 10 Apr 2022 at 12:04:05 (-0400), Greg Wooledge wrote: > On Sun, Apr 10, 2022 at 03:49:02PM +0100, Darac Marjal wrote: > > Systemd already supports this. > > > > * AccuracySec= Specify the accuracy the timer shall elapse with. [...] > > Within this time window, the expiry time shall be placed at a host-specific, > > randomized, but stable position. > > > > * RandomizedDelaySec = Delay the timer by a randomly selected, evenly > > distributed amount of time between 0 and the specified time value. > > > > > > So, "OnCalendar=daily" together with "AccuracySec=24h" *seems* to imply > > "once per day, but at a random time during the day". > > If that's the case, it's not working correctly on my system. mlocate > has OnCalendar=daily and AccuracySec=24h, but before I changed it, it > was scheduled to run *exactly* at midnight. > > /lib/systemd/system/man-db.timer has OnCalendar=daily and AccuracySec=12h > and it's scheduled to run *exactly* at midnight. > > /lib/systemd/system/logrotate.timer has OnCalendar=daily and AccuracySec=1h > and it's scheduled to run *exactly* at midnight.
I think that's because there are two more options whose default values are zero and false, so they're not specified in our .timer files. AIUI, setting RandomizedDelaySec=24hr would get you the effect it seems you expected above, but I seriously think you wouldn't want. AccuracySec appears to allow several expiring timers to be grouped into one instant if that instant is within the range allowed, hence minimising wakeups; RandomizedDelaySec does the opposite, spreading them out, hence minimising spikes in system load. If you set RandomizedDelaySec=24hr, then mlocate/whatever would run at random times of day each day. Setting FixedRandomDelay=true would make mlocate/whatever run at the same time each day, and that time would be whatever happened to be chosen on the first day. (I think buster/241 lacks the fixed one.) I'm quite happy for mlocate to run (almost) first thing in the morning when I turn on the computer (assuming I didn't run it beyond midnight last night). Cheers, David.
