[Bug 1783597] Update Released

[Brian Murray]

The verification of the Stable Release Update for ubuntu-release-
upgrader has completed successfully and the package is now being
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/1783597

Title:
  The disk-space-needed estimate doesn't account for the snaps

Status in ubuntu-release-upgrader package in Ubuntu:
  Fix Released
Status in ubuntu-release-upgrader source package in Disco:
  Fix Released
Status in ubuntu-release-upgrader source package in Eoan:
  Fix Released

Bug description:
  [Impact]

  Since there have been reports that users might fail to boot to a
  working gdm in the case of a full disk, we need to make sure users
  upgrading from and older release to disco/eoan have enough space for
  the upgrade to succeed. Currently we are installing snaps to replace
  certain debs on the system (+ refreshing existing snaps to newer
  channels/branches). The additional size required for the snap
  replacements was not taken into consideration when performing the
  upgrade, which might lead to edge-cases of users not having enough
  space for the upgrade to succeed.

  [Test Case]

  * Prepare a bionic machine
  * Make sure ubuntu-desktop and snapd are installed on it
  * Install core18 from stable and, for instance, gnome-characters from the stable/ubuntu-18.04 branch
  * Do snap list and snap refresh other gnome-related snaps to stable/ubuntu-18.04
  * Perform an upgrade to disco (with the --proposed option, to use disco-proposed)
  * Reboot
  * Make sure the update succeeded and all the installed gnome snaps now track stable/ubuntu-19.04 instead
  * Check /var/log/dist-upgrade/main.log and see if '/var' is listed in the calculated required space print-out

  Additional test case to make sure update-manager did not regress due
  to the changes:

  * On the newly upgraded system (or a new disco instance with ubuntu-release-upgrader upgraded to the version in disco-proposed), downgrade any of the installed packages
  * On the terminal, run `update-manager` and wait for the window to appear
  * Once the list of available upgrades appears, press the 'install now' button
  * Upgrades should install and no python traceback should be printed on the terminal

  [Regression Potential]

  As with any change touching the upgrade code-path, this change also carries a risk and should be well tested before going forward. That being said, the fix has been specifically basically limited to DistUpgradeQuirks to make regressions less likely. Additionally, unit tests have been added for every modified code-path.
  If any regressions should be found, the most likely place for those would be in size estimation, causing users to get notified of lack of space when they shouldn't. Another possible location would be all the things regarding replacing the debs with snaps - so either failures in snap replacement installation or refreshing.

  [Original Description]

  Looking at the code change recently made to install snaps on upgrade,
  it seems like there was no change made to the disk-space-estimate
  code. We had some reports recently that bionic might fail to boot to a
  working gdm on full disk so that could potentially be an important
  issue for upgraders

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