[Bug 1824088] Re: unattended upgrade ran one day after schedule

[Julian Andres Klode]

https://salsa.debian.org/apt-team/apt/-/merge_requests/115 implements
the proposed change for daily runs, and warns if intervals are
configured to anything other than 1 or 0 (and soon, always), telling
people to configure their systemd timer instead.

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Title:
  unattended upgrade ran one day after schedule

Status in apt package in Ubuntu:
  Triaged

Bug description:
  I have noticed a strange behaviour in unattended upgrades. The host in
  question is scheduled to run upgrades on Mondays every second week.
  However, this week it ran upgrades on Tuesday instead (2019-04-09).

  This is the first time I’ve noticed this behaviour. I checked the logs
  in /var/log/apt/history.log* and I saw that worked as intended up
  until this week. Upgrades ran as expected on 2019-03-11 and
  2019-03-25, which where both Mondays.

  The schedule was set with the line 'APT::Periodic::Unattended-Upgrade
  "14";' in the file /etc/apt/apt.conf.d/20auto-upgrades.

  Could it be daylight savings time that has caused skewing of the
  schedule?

  The server is located in Sweden and on 2019-03-31 we switched from CET
  to CEST. If the time diff is calculated with hours instead of calendar
  days passed, perhaps the missing hour on 2019-03-31 caused the
  scheduler to believe that on Monday 2019-03-08, two weeks (336 hours)
  had not yet passed.

  
  ADDITIONAL INFO

  Description:    Ubuntu 16.04.6 LTS
  Release:        16.04

  apt:
    Installed: 1.2.29ubuntu0.1
    Candidate: 1.2.31
    Version table:
       1.2.31 500
          500 http://se.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
   *** 1.2.29ubuntu0.1 500
          500 http://security.ubuntu.com/ubuntu xenial-security/main amd64 Packages
          100 /var/lib/dpkg/status
       1.2.10ubuntu1 500
          500 http://se.archive.ubuntu.com/ubuntu xenial/main amd64 Packages

  unattended-upgrades:
    Installed: 0.90ubuntu0.10
    Candidate: 0.90ubuntu0.10
    Version table:
   *** 0.90ubuntu0.10 500
          500 http://se.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
          500 http://se.archive.ubuntu.com/ubuntu xenial-updates/main i386 Packages
          500 http://security.ubuntu.com/ubuntu xenial-security/main amd64 Packages
          500 http://security.ubuntu.com/ubuntu xenial-security/main i386 Packages
          100 /var/lib/dpkg/status
       0.90 500
          500 http://se.archive.ubuntu.com/ubuntu xenial/main amd64 Packages
          500 http://se.archive.ubuntu.com/ubuntu xenial/main i386 Packages

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: apt 1.2.29ubuntu0.1
  ProcVersionSignature: Ubuntu 4.4.0-142.168-generic 4.4.167
  Uname: Linux 4.4.0-142-generic x86_64
  ApportVersion: 2.20.1-0ubuntu2.18
  Architecture: amd64
  Date: Wed Apr 10 09:06:49 2019
  InstallationDate: Installed on 2017-12-28 (467 days ago)
  InstallationMedia: Ubuntu-Server 16.04.3 LTS "Xenial Xerus" - Release amd64 (20170801)
  SourcePackage: apt
  UpgradeStatus: No upgrade log present (probably fresh install)

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