Bug#1032937: breaks upgrades if systemd-resolved can't run

[Michael Biebl]

Am 14.03.23 um 17:31 schrieb Luca Boccassi:

On Tue, 14 Mar 2023 18:03:53 +0200 =?utf-8?Q?Samuli_Suonp=C3=A4=C3=A4?=
<suon...@diurnalis.fi> wrote:

On 14. Mar 2023, at 17.34, Luca Boccassi <bl...@debian.org> wrote:

Exactly, so the admin shouldn't install a package that in the
description says:

"Installing this package automatically overwrites /etc/resolv.conf

and

switches it to be managed by systemd-resolved."

if that's not what they want to achieve. I agree that the
/etc/resolv.conf interface is garbage, but there's nothing we can

do

about it, that's just how it works.
This is the only way read-only images can be supported sanely.

Why exactly is it necessary to overwrite /etc/resolv.conf at

postinst, even if

the service will not and can not be started?

Wouldn’t it make more sense to make the symlink at a later stage? For
Instance when the service is actually started?

No, because at that point /etc might be part of a read-only filesystem
and thus it's too late.

There’s no point in having resolv.conf symlink to
/run/systemd/resolve/stub-resolv.conf when systemd-resolved is not

running.

Don't install it if you don't want it to run.

I might accept a patch that switches to using tmpfiles.d, as long as
the default is still to enable on install, and that taking a copy of
the existing resolv.conf is also done, and that it is proven to work on
a read-only image. That way it's easier to override it with a drop-in.
I am not going to write and test such patch though, someone else needs
to do it and send a MR on Salsa.

https://salsa.debian.org/debian/resolvconf/-/blob/unstable/debian/postinst#L101
https://git.launchpad.net/ubuntu/+source/systemd/tree/debian/systemd-resolved.postinst#n31

Would be a simple, 2-line patch

mkdir -p "${DPKG_ROOT}/run/systemd/resolve"


Regards,
Michael

A simple solution to this issue could be, to copy the existing /etc/resolv.conf to /run/systemd/resolve/stub-resolv.conf in postinst. If systemd-resolved is started, it will be overwritten properly, if not, the original resolv.conf should continue to work. This is how resolvconf does it and how the systemd-resolved package in Ubuntu does it: cp "${DPKG_ROOT}/etc/resolv.conf" "${DPKG_ROOT}/run/systemd/resolve/stub-resolv.conf"

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