[Bug 1974456] Re: regression: apt.postint fails if never previously configured

[Julian Andres Klode]

Verified.

For bionic I ran

mmdebstrap -v --keyring /usr/share/keyrings/ubuntu-archive-keyring.gpg
--aptopt='Acquire::http::proxy "http://localhost:8000/";' bionic bionic-
proposed http://archive.ubuntu.com/ubuntu 'deb
http://archive.ubuntu.com/ubuntu/ bionic-proposed main'

to enable proposed and this succeeded with

Setting up apt (1.6.16) ...

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

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https://bugs.launchpad.net/bugs/1974456

Title:
  regression: apt.postint fails if never previously configured

Status in apt package in Ubuntu:
  Confirmed
Status in apt source package in Bionic:
  Fix Committed
Status in apt source package in Focal:
  Fix Released

Bug description:
  [Impact]
  bootstrapping a system with apt that fixes #1968154 fails in focal and bionic, as they try to execute the config file that is being removed.

  This is not a problem on updates, only on new installs, so impact is
  limited to bootstrapping tools that enable -updates, such as
  mmdebstrap.

  [Test case]

  bootstrapping with -updates enabled can easily be tested with
  mmdebstrap:

  mmdebstrap -v focal ~/Projects/Ubuntu/Scratch/focal

  for example, on focal:

  Setting up apt (2.0.8) ...
  /var/lib/dpkg/info/apt.postinst: 65: /etc/kernel/postinst.d/apt-auto-removal: not found
  dpkg: error processing package apt (--configure):
   installed apt package post-installation script subprocess returned error exit status 127

  [Regression potential]
  We remove 5 lines from the shell postinst script, there could be syntax errors? But then we'd see those during upgrades, so practically none.

  [Original bug report]
  #1968154 removed `/etc/kernel/postinst.d/apt-auto-removal` in this patch:
  https://git.launchpad.net/ubuntu/+source/apt/commit/?id=f9d2d993687c0d5223c241956ef6a0aabcf15bf0

  ...but `apt.postinst` still tries to run it:

      # create kernel autoremoval blacklist on update
      if dpkg --compare-versions "$2" lt 0.9.9.3; then
          /etc/kernel/postinst.d/apt-auto-removal
      fi

  If I understand correctly, "$2" is the most-recently-configured-
  version, and if it's empty `dpkg --compare-versions lt` will evaluate
  to true.

  This fails when I'm building a focal (20.04) userspace from scratch:

      $ dpkg --configure -a
      [...]
      Setting up apt (2.0.8) ...
      /var/lib/dpkg/info/apt.postinst: 65: /etc/kernel/postinst.d/apt-auto-removal: not found
      dpkg: error processing package apt (--configure):
       installed apt package post-installation script subprocess returned error exit status 127

  It works with apt 2.0.6.

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