[Bug 1747499] Re: 98-reboot-required and Interaction with livepatch

[Olivier Gayot]

** Tags added: fr-1788

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Title:
  98-reboot-required and Interaction with livepatch

Status in unattended-upgrades package in Ubuntu:
  Confirmed
Status in update-notifier package in Ubuntu:
  Confirmed
Status in unattended-upgrades source package in Focal:
  New
Status in update-notifier source package in Focal:
  New

Bug description:
  
  [Impact]

   * If a system is using canonical livepatch, has it enabled, and
  patches are applied, it could be confusing for a user to receive a
  "system restart required" messages in the MOTD when logging in.

   * Livepatch is available on LTS releases. Thus, the users can be
  confused following a kernel update on 20.04.

   * The upload prevents update-notifier and unattended-ugprades hooks from adding "system restart"-related messages to motd when Livepatch is enabled.
  Livepatch, when enabled, already contributes to the motd message so there is no need to have duplicate (and sometimes contradictory) information.

  [Test Plan]

   * how to reproduce the bug:

     1. Install and boot a 20.04 server VM
     2. Make sure it runs a generic kernel (or another flavour that supports Livepatch)
     3. Enable Livepatch using the following command:
         $ ua attach <token>    # replace <token> by an actual contract token
     4. Upgrade the kernel (if you are already running the latest available kernel update, you can install a different flavour)
     5. Upon logging in again, the motd will show ***System restart required***.

   * other testing appropriate to perform before landing this update:

    * Making sure that the patch has no impact when livepatch is not enabled.
    * The motd should show ***System restart required*** after upgrading the kernel if livepatch is not enabled.

  [Where problems could occur]

   * The change updates a hook script in /etc/kernel/postinst.d/.
  Scripts in this directory are executing when upgrading / installing a
  kernel. If somehow the script is broken, it can prevent dpkg for
  succeeding when upgrading / installing the kernel.

   * If the implementation is wrong, we might end up "losing" the
  ***System restart required*** message when livepatch is disabled

  [Original bug description]

  If a system is using canonical livepatch, has it enabled, and patches
  are applied, it could be confusing for a user to receive a "system
  restart required" messages in the MOTD when logging in.

  That message, when present, is printed by 98-reboot-required which
  essentially just cats /var/run/reboot-required to stdout. That file is
  placed by packages that require a reboot so that they are properly
  used in their updated versions. Examples that come to mind are libc
  and the kernel.

  There is a secondary file that can be created which says which
  packages requested the reboot. That would be /var/run/reboot-
  required.pkgs

  Ideally that script should not print out the reboot required message
  if a) livepatch is installed and enabled; b) the only trigger for the
  reboot is a kernel update.

  For (a), one can use the command "ubuntu-advantage is-livepatch-
  enabled" and check $?. That is in the ubuntu-advantage-tools package.

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