[Bug 1615482] Re: apt-daily timer runs at random hours of the day

[Marius Gedminas]

My attempt to restrict unattended reboots to times between 0 and 6 AM
wasn't successful.  What I did is I created a /etc/systemd/system/apt-
daily.timer.d/override.conf with the following contents:

    [Timer]
    OnCalendar=*-*-* 00:00
    RandomizedDelaySec=6h

unattended-upgrade ran and rebooted my server at 1:27 AM, at which point
journalctl shows

    Nov 10 01:27:36 fridge systemd[1]: apt-daily.timer: Adding 4h 13min 49.738746s random time.
    Nov 10 01:27:36 fridge systemd[1]: Started Daily apt activities.

which would lead me to expect another run at 6:40 AM (which is already
outside my desired hours, but okay, not too bad).  Instead, what I got
was

    Nov 10 01:29:02 fridge systemd[1]: apt-daily.timer: Adding 3h 12min
35.192149s random time.

and then

    Nov 10 09:13:06 fridge systemd[1]: Starting Daily apt activities...

which rudely interrupted my morning Mutt session with another reboot.

Bug in systemd's timers?

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https://bugs.launchpad.net/bugs/1615482

Title:
  apt-daily timer runs at random hours of the day

Status in apt package in Ubuntu:
  Triaged

Bug description:
  apt, from 1.2.10 onwards (ie any version in Xenial, onwards) uses a
  systemd timer instead of a cron.daily job. This is a good thing,
  decoupling apt daily runs from the rest of cron, and ensuring other
  cron.daily jobs are not blocked by up to half an hour by the default
  settings of unattended-upgrades.

  However the policy chosen is to have the apt daily script run at a
  random hour of the day in a wrong headed attempt to reduce server
  load. This has the side effect of running unattended-upgrades at
  random hours of the day — such as business hours — rather than being
  confined to between 6:25am and 6:55am, using the defaults.

  A better policy would be to have the script activate at 6:00am plus an
  interval of 20 minutes at one second intervals reducing the impact of
  timezone population spikes, while still allowing unattended-upgrades
  to run within a predictable interval, before 7am.

  At the very least, some sort of note in the NEWS file detailing the
  new behaviour would be welcome.

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