[Bug 1874953] Re: dpkg: conffile difference visualizer subprocess returned error exit status 127

[Brian Murray]

The version of less from focal-proposed resolved the issue and I'm now
able to view the diff.

Configuration file '/etc/default/smartmontools'
 ==> Modified (by you or by a script) since installation.
 ==> Package distributor has shipped an updated version.
   What would you like to do about it ?  Your options are:
    Y or I  : install the package maintainer's version
    N or O  : keep your currently-installed version
      D     : show the differences between the versions
      Z     : start a shell to examine the situation
 The default action is to keep your current version.
*** smartmontools (Y/I/N/O/D/Z) [default=N] ? d
--- /etc/default/smartmontools  2020-07-01 15:02:20.945403642 -0700
+++ /etc/default/smartmontools.dpkg-new 2019-10-09 17:32:47.000000000 -0700
@@ -4,9 +4,6 @@
 # List of devices you want to explicitly enable S.M.A.R.T. for
 # Not needed (and not recommended) if the device is monitored by smartd
 #enable_smart="/dev/hda /dev/hdb"
-enable_smart="/dev/vda"
-# uncomment to start smartd on system startup
-#start_smartd=yes
 
 # uncomment to pass additional options to smartd on startup
 #smartd_opts="--interval=1800"

Configuration file '/etc/default/smartmontools'
 ==> Modified (by you or by a script) since installation.
 ==> Package distributor has shipped an updated version.
   What would you like to do about it ?  Your options are:
    Y or I  : install the package maintainer's version
    N or O  : keep your currently-installed version
      D     : show the differences between the versions
      Z     : start a shell to examine the situation
 The default action is to keep your current version.
*** smartmontools (Y/I/N/O/D/Z) [default=N] ? z
Useful environment variables:
 - DPKG_SHELL_REASON
 - DPKG_CONFFILE_OLD
 - DPKG_CONFFILE_NEW
Type 'exit' when you're done.
root at clean-xenial-amd64:/# apt-cache policy less
less:
  Installed: 551-1ubuntu0.1
  Candidate: 551-1ubuntu0.1
  Version table:
 *** 551-1ubuntu0.1 500
        500 http://ubuntu.osuosl.org/ubuntu focal-proposed/main amd64 Packages
        100 /var/lib/dpkg/status
     551-1 500
        500 http://ubuntu.osuosl.org/ubuntu focal/main amd64 Packages


** Tags removed: verification-needed verification-needed-focal
** Tags added: verification-done verification-done-focal

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https://bugs.launchpad.net/bugs/1874953

Title:
  dpkg: conffile difference visualizer subprocess returned error exit
  status 127

Status in dpkg package in Ubuntu:
  Invalid
Status in less package in Ubuntu:
  Fix Released
Status in smartmontools package in Ubuntu:
  Invalid
Status in dpkg source package in Focal:
  Invalid
Status in less source package in Focal:
  Fix Committed
Status in smartmontools source package in Focal:
  Invalid
Status in dpkg source package in Groovy:
  Invalid
Status in less source package in Groovy:
  Fix Released
Status in smartmontools source package in Groovy:
  Invalid
Status in dpkg package in Debian:
  New
Status in less package in Debian:
  Fix Committed

Bug description:
  [Impact]
  During a release upgrade to Ubuntu 20.04 LTS some users are not able to view the differences made to a configuration file during the upgrade process. This creates a bad user experience and leads to extra crash reports.

  [Test Case]
  1) Upgrade from a not usr-merged system (Ubuntu 16.04 LTS) to Ubuntu 18.04 LTS
  2) Install the smartmontools package
  3) Edit /etc/default/smartmontools (it's enough to just add a comment in there)
  4) Upgrade to Ubuntu 20.04 LTS (this requires do-release-upgrade -d as 20.04.1 is not out yet so release upgrades are not enabled)

  To test the fix in the version of less from focal-proposed some
  hackery of the release upgrader code will be necessary as it disables
  proposed during the upgrade process. After enabling -proposed for
  bionic you'll want to run do-release-upgrade -d, then cancel the
  upgrade. After which you can cd to /tmp/ubuntu-release-
  upgrader-$MKTMPDIR and edit DistUpgradeController.py and the if
  statement around line 641 re "Disable proposed on upgrade to a
  development release". Then run 'sudo ./focal'.

  [Regression Potential]
  None, as we are just calling update-alternatives in the preinst of less.

  
  Issue occurred on upgrade from 19.10 to 20.04

  ProblemType: PackageDistroRelease: Ubuntu 20.04
  Package: smartmontools 7.1-1build1
  ProcVersionSignature: Ubuntu 5.3.0-46.38-generic 5.3.18
  Uname: Linux 5.3.0-46-generic x86_64
  ApportVersion: 2.20.11-0ubuntu27
  Architecture: amd64
  CasperMD5CheckResult: skip
  Date: Fri Apr 24 21:33:08 2020
  ErrorMessage: conffile difference visualizer subprocess returned error exit status 127
  InstallationDate: Installed on 2011-06-18 (3233 days ago)InstallationMedia: Ubuntu-Server 11.04 "Natty Narwhal" - Release amd64 (20110426)
  Python3Details: /usr/bin/python3.8, Python 3.8.2, python3-minimal, 3.8.2-0ubuntu2
  PythonDetails: /usr/bin/python2.7, Python 2.7.18rc1, python-is-python2, 2.7.17-4
  RelatedPackageVersions:
   dpkg 1.19.7ubuntu3
   apt  2.0.2SourcePackage: smartmontools
  Title: package smartmontools 7.1-1build1 failed to install/upgrade: conffile difference visualizer subprocess returned error exit status 127
  UpgradeStatus: Upgraded to focal on 2020-04-25 (0 days ago)
  mtime.conffile..etc.default.smartmontools: 2017-12-08T19:12:02.064375
  mtime.conffile..etc.smartd.conf: 2017-12-08T20:27:28.727282

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