[Bug 1624681] Re: "Important" control field is a bit confusing

[Julian Andres Klode]

Essential packages not installed will be installed automatically by APT,
packages with the Important field will not be. Important also does not
have the same ordering requirements as Essential. It's main use case is
building configuration metapackages:

  https://juliank.wordpress.com/2012/01/24/managing-system-package-
selections-using-custom-meta-packages/

But yes, this is not specified at all - it is an APT-specific feature.
People do not like the field name, because it can be confused with
Priority: important, so it has not been standardized and included in
dpkg yet - also see
https://wiki.debian.org/Teams/Dpkg/Spec/ImportantField and
https://lists.debian.org/deity/2016/03/msg00025.html for further
information.

Once this has a new name and is standardized we can actually produce
good error messages.

** Changed in: apt (Ubuntu)
   Importance: Undecided => Low

** Changed in: apt (Ubuntu)
       Status: New => Triaged

** Bug watch added: Debian Bug tracker #826587
   http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=826587

** Also affects: apt (Debian) via
   http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=826587
   Importance: Unknown
       Status: Unknown

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https://bugs.launchpad.net/bugs/1624681

Title:
  "Important" control field is a bit confusing

Status in apt package in Ubuntu:
  Triaged
Status in init-system-helpers package in Ubuntu:
  New
Status in apt package in Debian:
  Unknown

Bug description:
  I'm using Ubuntu 16.10 dev and noticing that the package init seems to
  be the only one with the "Important" control field which seems to be a
  bit curious:

  - On removing a package with apt that has the "Important" field set to "yes" it seems to show the same warning like removing a package that has the "Essential" field set to "yes". Even the same term "essential" is used instead of "important" (maybe this should be changed?).
  - "man deb-control" does not know this field and removing a package with dpkg that has the "Important" field set to "yes" does not throw an error while removing a package that has the "Essential" field set to "yes" does.
  - I'm wondering what the difference between the "Essential" and "Important" field for apt is. I can't find any information about it and can't also find the manpage that documents the custom control fields that apt but not dpkg knows (does such a manpage exist?).
  - I'm also wondering why init uses this control field instead of the "Essential" control field as this would additionally prevent removing it by accident with dpkg.

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