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timer: Import defaults from systemd-sysupdate.timer #956

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timer: Import defaults from systemd-sysupdate.timer #956

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17 changes: 13 additions & 4 deletions systemd/bootc-fetch-apply-updates.timer
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Original file line number Diff line number Diff line change
@@ -1,14 +1,23 @@
[Unit]
Description=Apply bootc updates
Documentation=man:bootc(8)
# TODO: Tweak this to more strongly conditionalize on using
# bootc for host updates.
ConditionPathExists=/run/ostree-booted

[Timer]
# This is copied from systemd-sysupdate.timer; it's just an arbitrary
# starting point.
#
# Trigger the update 1 hour after boot, and then – on average – every 6h, but
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every 6h should be every 4h here? If it's randomly picking between 2h and 6h. Maybe I am misunderstanding something though.

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The comment here is mostly copied verbatim, so any errors are in the original. But it is good to double check. In looking at this...I think offhand you're right that the comment here is wrong or misleading.

It does seem offhand to me that the timer is going to be actually on average 2h (after initial bootup and completion of the timer, ignoring the time it takes to actually execute the check).

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I am going to just jot down my flimsy understanding here of how this would play out. Corrections very much welcomed 😄

  • T-0: system boots
  • T+1h: OnBootSec=1h is "triggered", but doesn't fire immediately due to RandomizedDelaySec=4h being applied to all "subtimers" within this timer?
  • T+~3h: (assume RandomizedDelaySec=4h always just produces 2h) The timer actually fires for the first time, activating the associated service unit
  • T+~5h: OnUnitActiveSec=2h is "triggered" but as above with OnBootSec doesn't fire immediately due to delay
  • T+~7h: The timer fires the service for the second time
  • (loop here)
  • T+11h: service fires
  • T+15h: service fires
  • (and so on looping)
  • I guess Saturday at 00:00 the OnCalendar bit fires, but is still subjected to the ~2h delay
  • Saturday 2am: service fires
  • (subtimer for OnUnitActive resets?)
  • Saturday 4am: OnUnitActive triggered but delays
  • Saturday 6am: service fires

Something like that?

# randomly distributed in a 2h…6h interval. In addition trigger things
# persistently once on each Saturday, to ensure that even on systems that are
# never booted up for long we have a chance to do the update.
OnBootSec=1h
# This time is relatively arbitrary and obviously expected to be overridden/changed
OnUnitInactiveSec=8h
# When deploying a large number of systems, it may be beneficial to increase this value to help with load on the registry.
RandomizedDelaySec=2h
OnUnitActiveSec=2h
OnCalendar=Sat
RandomizedDelaySec=4h
Persistent=yes

[Install]
WantedBy=timers.target
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