Re: Bug#978636: move to merged-usr-only?
Am Di., 29. Dez. 2020 um 23:13 Uhr schrieb Marco d'Itri <md@linux.it>:
>
> On Dec 29, Matthias Klumpp <matthias@tenstral.net> wrote:
>
> > For package upgrades, we can already perform so-called "offline
> > upgrades", where the system reboots into a smaller systemd target,
> > applies all updates and then reboots again into the updated system.
> > This is implemented in PackageKit as an option and used by GNOME.
> > Fwupd uses similar concepts for certain firmware updates as well.
> > Maybe hooking into these facilities is also an option for the usrmerge
> > upgrade? (unless of course systemd is still interfering even in a
> > minimal target, that would be a dealbreaker).
> It depends on which units are started (this trouble is caused by the
> ProtectSystem directive and maybe others like it): having usrmerge
> stop and then restart the daemons involved would work as well, but I am
> not sure of how many corner cases (gdm...) we would find before just
> rebooting would become simpler again.
> I think that depending on PackageKit would be more complex than an
> initramfs-tools hook, since just about everybody is supposed to have
> that around.
You wouldn't have to depend on PackageKit, the offline-upgrades stuff
can be implemented by other tools that aren't PK as well (you could
pretty much use the same mechanism, with some safeguards to not
interfere with PK/GNOME). However, ensuring that no service with
ProtectSystem starts may be a problem, as that feature is used quite
extensively by services that are part of the systemd project, and I
don't know whether it is possible to exclude them all from a potential
usrmerge target without causing other problems.
Also, of course this would only work on systemd systems, in the same
way that the initramfs-tools solution won't work for Dracut users.
Looks like quite a tricky problem, but one that could definitely be
addressed by the project.
Cheers,
Matthias
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