[Bug 1889190] Re: ldconfig is still deferred in libc6.preinst

[Balint Reczey]

18.04->20.04 upgrade breaks with the reproducer:

...


Preparing to unpack .../libc6_2.31-0ubuntu9_amd64.deb ...

Progress: [ 38%]
ldconfig: wrapper deferring update (trigger activated)
Checking for services that may need to be restarted...
Checking init scripts...
Checking for services that may need to be restarted...
Checking init scripts...
dpkg: error processing archive /var/cache/apt/archives/libc6_2.31-0ubuntu9_amd64.deb (--unpack):
 new libc6:amd64 package pre-installation script subprocess returned error exit status 20
Selecting previously unselected package libcrypt1:amd64.
dpkg: considering deconfiguration of libc6:amd64, which would be broken by installation of libcrypt1:amd64 ...
dpkg: yes, will deconfigure libc6:amd64 (broken by libcrypt1:amd64)
Preparing to unpack .../libcrypt1_1%3a4.4.10-10ubuntu4_amd64.deb ...
De-configuring libc6:amd64 (2.27-3ubuntu1.2) ...

Progress: [ 44%]
Unpacking libcrypt1:amd64 (1:4.4.10-10ubuntu4) ...
Replacing files in old package libc6:amd64 (2.27-3ubuntu1.2) ...

Progress: [ 50%]
Errors were encountered while processing:
 /var/cache/apt/archives/libc6_2.31-0ubuntu9_amd64.deb
ERROR: Cannot create report: [Errno 17] File exists: '/var/crash/libc6.0.crash'
Exception during pm.DoInstall():  E:Sub-process /usr/bin/dpkg returned an error code (1)

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https://bugs.launchpad.net/bugs/1889190

Title:
  ldconfig is still deferred in libc6.preinst

Status in glibc package in Ubuntu:
  New
Status in glibc source package in Focal:
  New

Bug description:
  [Impact]

   * Upgrade from Bionic to Focal may break
   * The upload really forces 

  [Test Case]

  $ lxc launch ubuntu:bionic bb-glibc-upgrade
  $ lxc shell bb-glibc-upgrade 
  # export LDCONFIG_TRIGGER_DEBUG=1
  #  apt update -qq && apt upgrade -qq -y && do-release-upgrade -d
  ...

  With the broken version the following message can be observed:
  ..
  Preparing to unpack .../libc6_2.31-0ubuntu9_amd64.deb ...

  Progress: [ 38%]
  ldconfig: wrapper deferring update (trigger activated)
  ...

  The fixed version runs ldconfig immediately after unpacking libc6.

  
  [Regression Potential] 

  * Very small, the fix is literally adding one single character to
  properly set LDCONFIG_NOTRIGGER.

  [Other Info]

  Fix: 
  --- a/debian/debhelper.in/libc.preinst
  +++ b/debian/debhelper.in/libc.preinst
  @@ -22,7 +22,7 @@ kfreebsd_compare_versions () {
   # libcrypt1 breaks/replaces libc6 (<< 2.31). cannot use a pre-depends on libcrypt1
   # call ldconfig unconditionally for the first libc6 depending on libcrypt1
   if [ -n "$preversion" ] && dpkg --compare-versions "$preversion" lt 2.31-0ubuntu2; then
  -       LCONFIG_NOTRIGGER=y
  +       LDCONFIG_NOTRIGGER=y
          export LDCONFIG_NOTRIGGER
          ldconfig || ldconfig --verbose
   fi

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