/usr/share/ubuntu-release-upgrader/removal_blacklist.cfg is in ubuntu-release-upgrader-core 1:16.04.12.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 | # blacklist of packages that should never be removed
ubuntu-standard
ubuntu-minimal
ubuntu-desktop$
kubuntu-desktop
xubuntu-desktop
lubuntu-desktop
mythbuntu-desktop
ubuntustudio-desktop
ubuntu-gnome-desktop
ubuntu-mate-core
ubuntu-mate-cloudtop
ubuntu-mate-desktop
# ubuntu-release-upgrader should not remove itself or update-manager
update-manager$
update-manager-core
ubuntu-release-upgrader-core
# postgresql (LP: #871893)
^postgresql-.*[0-9]\.[0-9].*
# the upgrade runs in it
^screen$
# unity
unity$
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