apt-get dist-upgrade keeping back some packets

[Gionatan Danti <g.danti@assyoma.it>]

Hi all,
I have a question about apt-get dist-upgrade refusing to update some 
packages:

root@localhost:/var/log/apt# apt-get dist-upgrade
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Calculating upgrade... Done
The following packages have been kept back:
  grub-efi-amd64 grub-efi-amd64-bin grub-efi-amd64-signed 
libnss-mymachines libnss-systemd libpam-systemd libpython3-dev 
libpython3-stdlib libpython3.10 libpython3.10-dev libpython3.10-minimal 
libpython3.10-stdlib libsystemd0 libudev1
  python3 python3-dev python3-distutils python3-gdbm python3-lib2to3 
python3-minimal python3-tk python3.10 python3.10-dev python3.10-minimal 
systemd systemd-container systemd-sysv systemd-timesyncd udev
The following packages will be upgraded:
  bind9-dnsutils bind9-host bind9-libs libpcre2-8-0 python3-oauthlib
5 upgraded, 0 newly installed, 0 to remove and 29 not upgraded.
5 standard security updates
Need to get 1,719 kB of archives.
After this operation, 3,072 B of additional disk space will be used.
Do you want to continue? [Y/n] n
Abort.

To update, I had to specify all the packages on the command line after 
the dist-upgrade command (or use aptitude full-upgrade). Enabling debug 
via resulted in something similar to that:

root@localhost:/etc/apt# apt-get -oDebug::pkgProblemResolver=1 
-oDebug::BuildDep=1 -oDebug::pkgDepCache::AutoInstall=1 
-oDebug::pkgDepCache::Marker=1 -oDebug::pkgOrderList=1 
-oDebug::pkgProblemResolver::ShowScores=1 -oDebug::pkgDpkgPm=1 
-opkgDPkgPm::Item=1 dist-upgrade 2>&1 | less
Calculating upgrade...Starting pkgProblemResolver with broken count: 0
Settings used to calculate pkgProblemResolver::Scores::
  Required => 3
  Important => 2
  Standard => 1
  Optional => -1
  Extra => -2
  Essentials => 100
  InstalledAndNotObsolete => 1
  Pre-Depends => 1
  Depends => 1
  Recommends => 1
  Suggests => 0
  Conflicts => -1
  Breaks => -1
  Replaces => 0
  Obsoletes => 0
  Enhances => 0
  AddProtected => 10000
  AddEssential => 5000
Show Scores
10539 libsystemd0:amd64 < 249.11-0ubuntu3.6 @ii pmK >
10419 python3:amd64 < 3.10.6-1~22.04 @ii pmK >
10320 libudev1:amd64 < 249.11-0ubuntu3.6 @ii pmK >
10206 python3-minimal:amd64 < 3.10.6-1~22.04 @ii pmK >
10206 libpython3-stdlib:amd64 < 3.10.6-1~22.04 @ii pmK >
10150 systemd-sysv:amd64 < 249.11-0ubuntu3.6 @ii pmK >
...

It seems to me that some package is marked as Protected. However, 
running dpkg on one of these packages show no 
protected/essential/important flag:

root@localhost:/var/cache# dpkg-query -Wf 'package:${Package} 
arch:${Architecture} bugs:${Bugs} ess:${Essential} pri:${Priority} 
pro:${Protected} imp:${Important}\n' libsystemd0
package:libsystemd0 arch:amd64 bugs: ess:no pri:optional pro:no imp:

So, why apt-get dist-upgrade refuses to upgrade? How it collect the list 
of protected packages?
Thanks.

--
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@assyoma.it - info@assyoma.it
GPG public key ID: FF5F32A8