package smartmontools 7.1-1build1 failed to install/upgrade: conffile difference visualizer subprocess returned error exit status 127

[Laurent Bonnaud]

During an upgrade from eoan to focal I got the following error:

 package:smartmontools:7.1-1build1
 Installing new version of config file /etc/init.d/smartmontools ...

 Configuration file '/etc/smartd.conf'
  ==> 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.
 *** smartd.conf (Y/I/N/O/D/Z) [default=N] ? d
 sh: 1: pager: not found
 diff: standard output: Broken pipe
 dpkg: error processing package smartmontools (--configure):
  conffile difference visualizer subprocess returned error exit status 127

ProblemType: Package
DistroRelease: Ubuntu 20.04
Package: smartmontools 7.1-1build1
Uname: Linux 5.6.2-050602-generic x86_64
ApportVersion: 2.20.11-0ubuntu22
Architecture: amd64
Date: Thu Apr 2 19:58:06 2020
ErrorMessage: conffile difference visualizer subprocess returned error exit status 127
Python3Details: /usr/bin/python3.8, Python 3.8.2, python3-minimal, 3.8.2-0ubuntu1
PythonDetails: /usr/bin/python3.8, Python 3.8.2, python-is-python3, 3.8.2-3
RelatedPackageVersions:
 dpkg 1.19.7ubuntu2
 apt 2.0.1
SourcePackage: 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 2020-04-02 (0 days ago)
mtime.conffile..etc.smartd.conf: 2019-06-28T19:35:09.428956

[Christian Ehrhardt  (paelzer)]

Hmm, the pager is called from dpkg to show the diff in your case.
This didn't change and dpkg doesn't do anything magic.

I can only assume that you might have the "pager" itself setup in an odd way.
Due to a bug or intentional - I don't know.

Could you report back the output of:

$ update-alternatives --display pager

That most likely should look like:
root@f2:~# update-alternatives --display pager
pager - auto mode
  link best version is /usr/bin/less
  link currently points to /usr/bin/less
  link pager is /usr/bin/pager
  slave pager.1.gz is /usr/share/man/man1/pager.1.gz
/bin/more - priority 50
  slave pager.1.gz: /usr/share/man/man1/more.1.gz
/usr/bin/less - priority 77
  slave pager.1.gz: /usr/share/man/man1/less.1.gz

If that is broken then I could see how the above error could happen.

Finally if that is not a local setup issue, then still it would be more likely in dpkg and or less (as the common and default pager - both are auto-installed and I see them updated in your log). I'll re-assign the bug tasks accordingly.

[Laurent Bonnaud (laurent-bonnaud)]

Here it is on my system:

$ update-alternatives --display pager
pager - auto mode
  link best version is /usr/bin/less
  link currently points to /usr/bin/less
  link pager is /usr/bin/pager
  slave pager.1.gz is /usr/share/man/man1/pager.1.gz
/bin/more - priority 50
  slave pager.1.gz: /usr/share/man/man1/more.1.gz
/usr/bin/less - priority 77
  slave pager.1.gz: /usr/share/man/man1/less.1.gz
/usr/bin/w3m - priority 25
  slave pager.1.gz: /usr/share/man/man1/w3m.1.gz

However this output is for my system in its current state, that has been fixed by finishing the eoan -> focal upgrade. The alternative was probably transiently broken during the upgrade.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Mikko (mikko911)]

Same issue occurred here during 19.10 -> 20.04 upgrade.

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
sh: 1: pager: not found
diff: standard output: Broken pipe

Pager worked fine during the upgrade with packages before and after smartmontools.