[Bug 1771894] Update Released

[Brian Murray]

The verification of the Stable Release Update for update-manager has
completed successfully and the package has now been released to
-updates.  Subsequently, the Ubuntu Stable Release Updates Team is being
unsubscribed and will not receive messages about this bug report.  In
the event that you encounter a regression using the package from
-updates please report a new bug using ubuntu-bug and tag the bug report
regression-update so we can easily find any regressions.

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https://bugs.launchpad.net/bugs/1771894

Title:
  /usr/bin/update-
  manager:TypeError:<lambda>:on_button_install_clicked:start_install:_start_pane:start:unwind_generator

Status in update-manager package in Ubuntu:
  Invalid
Status in update-manager source package in Xenial:
  Fix Released

Bug description:
  [Impact]

  The backend API change made update-manager crash when the updated
  incompatible backend was loaded to the not updated running update-
  manager process.

  The issue causes crashes upon update-manager updates harming the
  upgrade experience for users.

  The fix avoids lazy loading of the backend modules but still honors
  the backend selection options.

  [Test Case]


  1. Start with a fully upgraded system and downgrade a few packages to let u-m upgrade them and also downgrade update-manager to 1:16.04.12 or earlier:
  $ sudo eatmydata apt install -y --allow-downgrades gnome-software=3.28.1-0ubuntu4 gnome-software-common=3.28.1-0ubuntu4
  $ sudo apt install update-manager=1:16.04.12 update-manager-core=1:16.04.12 python3-update-manager=1:16.04.12

  2. Start u-m with:
   $ update-manager --no-update

  3. Upgrade update-manager to a still not fixed version to observe the crash:
  $ sudo apt install update-manager=1:16.04.14 update-manager-core=1:16.04.14 python3-update-manager=1:16.04.14

  ... or to the fixed version to a see the crash not happening in step
  4:

  $ sudo apt install update-manager=1:16.04.15 update-manager-
  core=1:16.04.15 python3-update-manager=1:16.04.15

  
  4. Press "Install Now" on u-m GUI.
   The fixed u-m will successfully perform the installation, the unfixed one will fail with:
  TypeError: commit() missing 1 required positional argument: 'pkgs_remove'

  [Regression Potential]

  The change to the backend API could cause u-m not able to remove
  unused kernels, but in my testing this feature still worked.

  [Original Bug Text]

  The Ubuntu Error Tracker has been receiving reports about a problem regarding update-manager.  This problem was most recently seen with package version 1:18.04.11, the problem page at https://errors.ubuntu.com/problem/310b9890e139c17b61faeee8f50078909283794e contains more details, including versions of packages affected, stacktrace or traceback, and individual crash reports.
  If you do not have access to the Ubuntu Error Tracker and are a software developer, you can request it at http://forms.canonical.com/reports/.

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