[Bug 1781412] Update Released

[Steve Langasek]

The verification of the Stable Release Update for ubuntu-release-
upgrader 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/1781412

Title:
  do-release-upgrade crashed with UnboundLocalError in
  _replaceDebsWithSnaps(): local variable 'proc' referenced before
  assignment

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

Bug description:
  Adding support for transitioning debs to snaps when upgrading from
  16.04 to 18.04, bug 1780841, ended up creating a crash in a specific
  scenario.

  [Test Case]
  1) Install and Ubuntu 16.04 desktop system
  2) Modify /etc/hosts so api.snapcraft.io resolves to 127.0.0.1
  3) Upgrade to Ubuntu 18.04 using u-r-u 18.04.20 (sudo ./bionic --frontend DistUpgradeViewText)
  4) Observe the Traceback in this bug report

  N.B. You'll need to manually download and extract the release upgrader
  tarball from http://archive.ubuntu.com/ubuntu/dists/bionic-
  proposed/main/dist-upgrader-all/current/ since the upgrade is to the
  development and proposed release.

  I was testing a release upgrade from Ubuntu 16.04 to Ubuntu 18.04
  where I had no connectivity to the snap store and encountered this
  crash.

  ProblemType: CrashDistroRelease: Ubuntu 18.04
  Package: ubuntu-release-upgrader-core 1:18.04.20
  ProcVersionSignature: Ubuntu 4.4.0-121.145-generic 4.4.117
  Uname: Linux 4.4.0-121-generic x86_64
  ApportVersion: 2.20.9-0ubuntu7.2
  Architecture: amd64
  CrashDB: ubuntu
  Date: Wed Jul 11 20:03:49 2018
  ExecutablePath: /usr/bin/do-release-upgrade
  ExecutableTimestamp: 1531169948
  InstallationDate: Installed on 2016-10-04 (645 days ago)
  InstallationMedia: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
  InterpreterPath: /usr/bin/python3.5
  PackageArchitecture: all
  ProcCmdline: /usr/bin/python3 ./bionic --frontend DistUpgradeViewText
  ProcCwd: /tmp/u-r-u
  ProcEnviron:
   TERM=screen
   SHELL=/bin/bash
   PATH=(custom, no user)
   LANG=en_US.UTF-8
   LC_CTYPE=en_US.UTF-8
  Python3Details: /usr/bin/python3.6, Python 3.6.5, python3-minimal, 3.6.5-3ubuntu1
  PythonArgs: ['/usr/bin/do-release-upgrade', '--frontend', 'DistUpgradeViewText']
  PythonDetails: /usr/bin/python2.7, Python 2.7.15rc1, python-minimal, 2.7.15~rc1-1SourcePackage: ubuntu-release-upgrader
  Title: do-release-upgrade crashed with UnboundLocalError in _replaceDebsWithSnaps(): local variable 'proc' referenced before assignment
  UpgradeStatus: Upgraded to bionic on 2018-07-12 (0 days ago)
  UserGroups:

  modified.conffile..etc.update-manager.release-upgrades: [modified]
  mtime.conffile..etc.update-manager.release-upgrades: 2016-10-04T13:43:38.934395

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