[Bug 1534374] Re: unable to upgrade to 15.04 due to libstdc++6 SRU

[Christoph Burschka]

Re #2:
> The version of libstdc++6 in vivid comes from gcc-4.9 source. There has been an SRU of gccgo-4.9 to trusty, which requires it to build a gcc-4.9-base package, whose version number is higher in trusty than in vivid; and libstdc++6 requires the matching version of gcc-4.9-base. This prevents upgrading anything that depends on libstdc++6.
> 
> This problem is specific to upgrades between trusty and vivid; libstdc++6 in wily is built from gcc 5 so depends on gcc-5-base instead of gcc-4.9-base, removing the problem.

>From this, I speculated that the obstruction in the upgrade path *might*
be cleared by manually up- (or rather down-) grading gcc-4.9-base from
the 4.9.3 version used in 14.04/trusty to the 4.9.2 version used in
15.04/vivid.

So I downloaded the package
(http://packages.ubuntu.com/vivid/gcc-4.9-base), manually installed it
with dpkg, and attempted to run do-release-upgrade again.

I haven't actually upgraded yet, but the error is gone now. The upgrade
path can be calculated successfully:

> 38 packages are going to be removed. 353 new packages are going to be 
> installed. 2364 packages are going to be upgraded.

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https://bugs.launchpad.net/bugs/1534374

Title:
  unable to upgrade to 15.04 due to libstdc++6 SRU

Status in ubuntu-release-upgrader package in Ubuntu:
  Triaged

Bug description:
  initially had a problem with X when i installed a new Nvidia video
  card.  got that working but only one monitor was functioning (other is
  displayport).  Thought maybe upgrading to a new release might fix the
  problem.  Software update only offered 15.04, so I said ok and tried
  to upgrade.  It crashed with the info attached.  rebooted just in
  case, but still get the same problem

  ProblemType: Bug
  DistroRelease: Ubuntu 14.04
  Package: ubuntu-release-upgrader-core 1:0.220.8
  ProcVersionSignature: Ubuntu 3.16.0-57.77~14.04.1-generic 3.16.7-ckt20
  Uname: Linux 3.16.0-57-generic x86_64
  ApportVersion: 2.14.1-0ubuntu3.19
  Architecture: amd64
  CrashDB: ubuntu
  Date: Thu Jan 14 18:38:01 2016
  InstallationDate: Installed on 2015-03-14 (306 days ago)
  InstallationMedia: Ubuntu 14.04.2 LTS "Trusty Tahr" - Release amd64 (20150218.1)
  PackageArchitecture: all
  ProcEnviron:
   TERM=xterm
   PATH=(custom, no user)
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  SourcePackage: ubuntu-release-upgrader
  UpgradeStatus: Upgraded to trusty on 2016-01-14 (0 days ago)
  VarLogDistupgradeTermlog:
   
  mtime.conffile..etc.update.manager.release.upgrades: 2016-01-14T18:29:51.136835

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