deb to snap transition uses an ubuntu release channel for the core18 snap

[Brian Murray]

[Impact]

During distro upgrades, additional logic exists that replaces existing debs with snaps and refreshes existing, installed snaps to the branch of the series we're upgrading to (e.g. from stable/ubuntu-18.04 to stable/ubuntu-19.04 etc.). However, the upgrader tries to apply the logic for all the snaps it 'supports' in migration, even though snaps like core18 do not have per-series branches (and will never have). This causes non-fatal failures during installation/refresh of the core18 snap on upgrades. Even though this does not cause a crash or error, and in theory should should not cause any trouble as core18 *should* be pulled in as a dependency of the other snaps, it is invalid behavior and might result in core18 not being present on the end system. Upgrades should not perform commands that fail, if possible.

[Test Case]

* Prepare a bionic machine
* Make sure ubuntu-desktop and snapd are installed on it
* Make sure core18 is *not* installed on the system - if there are any snaps installed, remove them
* Perform an upgrade to disco (with the --proposed option, to use disco-proposed)
* Reboot
* Make sure that the upgrade succeeded
* Check if core18 is installed, open /var/log/dist-upgrade/main.log and look for 'install of snap core18', make sure the command succeeded

[Regression Potential]

The changes have been constrained to the DistUpgradeQuirks place, only to the snap handling pieces. So any possible regressions should be visible in the snap replacement/refresh areas. Most probable ones would be for the snaps not being installed/refreshed properly, or using the wrong channels/branches.

[Original Description]

The release upgrader (DistUpgradeQuirks.py) tries to run the following command when upgrading a system without snaps installed to Ubuntu 19.10 (eoan):

snap install --channel stable/ubuntu-19.10 core18

This channel does not exist and the release upgrade will fail e.g.:

2019-08-23 03:24:45,533 DEBUG quirks: running eoanPostUpgrade
2019-08-23 03:24:45,533 DEBUG running Quirks.eoanPostUpgrade
2019-08-23 03:24:51,547 DEBUG install of snap core18 failed
2019-08-23 03:25:51,348 DEBUG install of snap gnome-3-28-1804 succeeded

The quirk should be updated so that an ubuntu release channel is not used when installing the core18 snap.

[Launchpad Janitor (janitor)]

This bug was fixed in the package ubuntu-release-upgrader - 1:19.10.11

---------------
ubuntu-release-upgrader (1:19.10.11) eoan; urgency=medium

  * DistUpgrade/DistUpgradeQuirks.py, DistUpgrade/DistUpgradeCache.py:
    Modify DistUpgradeQuirks to calculate extra space needed for snaps that
    need to be installed during upgrade (replacing old debs) and add that to
    estimates done in checkFreeSpace(). (LP: #1783597)
  * DistUpgrade/DistUpgradeQuirks.py: Make sure snaps like core18 are not
    refreshed/installed from the stable/ubuntu-VERSION branch but instead use
    stable on upgrades. (LP: #1841225)

 -- Łukasz 'sil2100' Zemczak <email address hidden> Tue, 03 Sep 2019 15:58:38 +0200

[Brian Murray (brian-murray)]

Hello Brian, or anyone else affected,

Accepted ubuntu-release-upgrader into disco-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/ubuntu-release-upgrader/1:19.04.16.7 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested and change the tag from verification-needed-disco to verification-done-disco. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-disco. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

[Łukasz Zemczak (sil2100)]

Verified ubuntu-release-upgrader 19.04.16.7 as per the test-case.

I set up a multipass bionic system, switched /etc/update-manager/release-upgrades to Prompt=normal, installed ubuntu-desktop and made sure there is no core18 snap installed. I then proceeded with running `do-release-upgrade --frontend DistUpgradeView --proposed`. The upgrade succeeded,confirmed that 19.04.16.7 was used [1] and checked that in the end all snaps got installed with the right channels selected (stable for core18 and stable/ubuntu-19.04 for others).

[1] 2019-10-09 14:14:11,811 INFO release-upgrader version '19.04.16.7' started

[Launchpad Janitor (janitor)]

This bug was fixed in the package ubuntu-release-upgrader - 1:19.04.16.7

---------------
ubuntu-release-upgrader (1:19.04.16.7) disco; urgency=medium

  * DistUpgrade/DistUpgradeQuirks.py, DistUpgrade/DistUpgradeCache.py:
    Modify DistUpgradeQuirks to calculate extra space needed for snaps that
    need to be installed during upgrade (replacing old debs) and add that to
    estimates done in checkFreeSpace(). (LP: #1783597)
  * DistUpgrade/DistUpgradeCache.py: Make sure checkFreeSpace() still works for
    update-manager with its own implementation of MyCache.
  * DistUpgrade/DistUpgradeQuirks.py: Make sure snaps like core18 are not
    refreshed/installed from the stable/ubuntu-VERSION branch but instead use
    stable on upgrades. (LP: #1841225)

 -- Łukasz 'sil2100' Zemczak <email address hidden> Mon, 09 Sep 2019 15:41:12 +0200

[Brian Murray (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.