Hi,

I'm trying to build a small script to synchronize the package
installation sets of a bunch of machines. My current approach is to
simply run

dpkg --clear-selections
dpkg --set-selections <packages.txt
apt-get --yes dselect-upgrade

I believe that this is the only interface that allows me to set the
package selection without having to compare current and desired list. To
get started, I first tried what would happen if I cleared the entire list:

root@57ac7d42f84f:/# dpkg --clear-selections
root@57ac7d42f84f:/# apt-get dselect-upgrade
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following packages will be REMOVED:
adduser apt debian-archive-keyring e2fsprogs gpgv libapt-pkg6.0
libcom-err2 libext2fs2 libffi8 libgnutls30 libhogweed6 libidn2-0
libnettle8 libp11-kit0 libseccomp2 libsemanage-common libsemanage2
libsepol2 libss2 libstdc++6 libtasn1-6 libunistring2 libxxhash0
logsave mount passwd tzdata
WARNING: The following essential packages will be removed.
This should NOT be done unless you know exactly what you are doing!
apt adduser (due to apt) gpgv (due to apt)
libapt-pkg6.0 (due to apt) debian-archive-keyring (due to apt)
libgnutls30 (due to apt) libseccomp2 (due to apt)
libstdc++6 (due to apt) e2fsprogs libcom-err2 (due to e2fsprogs)
libext2fs2 (due to e2fsprogs) libss2 (due to e2fsprogs)
logsave (due to e2fsprogs)
0 upgraded, 0 newly installed, 27 to remove and 0 not upgraded.
After this operation, 30.4 MB disk space will be freed.
E: Removing essential system-critical packages is not permitted.
This might break the system.

As far as I can see, there are two things apt and dpkg disagree on:

- whether apt itself is Essential

This is understandable, apt special-cases itself, and for a good reason.
I have no problem hardcoding an "apt install" into my package selection,
that solves this nicely.

- whether e2fsprogs is Essential

This is only Important, not Essential, so dpkg marks it "deinstall", and
apt doesn't want to remove it.

Outside of a container, obviously there will be more "Important"
packages. I can hardcode a sensible package set to have something that
works for me for now, but medium term I will probably have to explain
this script to someone else.

The obvious problem with this interface is that half of it is provided
by one tool, and half of it by another, and these implementations have incompatible worldviews that the user of the interface needs to be aware
of, because it was never designed to be cohesive. Also, the name "dselect-upgrade" suggests that this is really an atavism. A useful one,
but nonetheless probably not meant to be officially supported.

Since this functionality is useful, it would be nice to have a proper
supported way to do this.

Simon

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Simon Richter:

Hi,

[...]

This is understandable, apt special-cases itself, and for a good reason.
I have no problem hardcoding an "apt install" into my package selection,
that solves this nicely.

 - whether e2fsprogs is Essential

This is only Important, not Essential, so dpkg marks it "deinstall", and
apt doesn't want to remove it.

Hi,


I think your problem here would be solved if `e2fsprogs` used the new `Protected` field rather than the legacy `XB-Important` field. As I
recall, both apt and dpkg knows about the former while the later was an
apt only thing. See
https://lists.debian.org/debian-dpkg/2020/03/msg00002.html

For the rest, I have no comments (not my field of expertise).

Best regards,
Niels

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Hi!

On Thu, 2024-02-29 at 15:34:48 +0900, Simon Richter wrote:

As far as I can see, there are two things apt and dpkg disagree on:

- whether apt itself is Essential

This is understandable, apt special-cases itself, and for a good reason. I have no problem hardcoding an "apt install" into my package selection, that solves this nicely.

Right. To me this seems to indicate apt should provide its own
interface to set selections (perhaps through apt-mark or similar), so
that then it can inject itself into dpkg worldview as it does when
operating itself.

- whether e2fsprogs is Essential

This is only Important, not Essential, so dpkg marks it "deinstall", and apt doesn't want to remove it.

As Niels has pointed out, this would work automatically (for dpkg), if e2fsprogs used Protected instead of Important.

The obvious problem with this interface is that half of it is provided by
one tool, and half of it by another, and these implementations have incompatible worldviews that the user of the interface needs to be aware of, because it was never designed to be cohesive. Also, the name "dselect-upgrade" suggests that this is really an atavism. A useful one, but nonetheless probably not meant to be officially supported.

Since this functionality is useful, it would be nice to have a proper supported way to do this.

I think the different worldviews are ok, but as mentioned above, and
to avoid layer violations, to me this seems like the upper layer would
need to provide a wrapper for it.

If there's stuff to improve from the interface in the dpkg side I'm
happy to also discuss that.

Thanks,
Guillem

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