[systemd-devel] How to factory reset?

Zbigniew Jędrzejewski-Szmek zbyszek at in.waw.pl
Thu Mar 12 17:16:05 PDT 2015

On Tue, Mar 10, 2015 at 10:23:23PM +0100, Tobias Hunger wrote:
> On Tue, Mar 10, 2015 at 9:33 PM, Tobias Hunger <tobias.hunger at gmail.com> wrote:
> >> presets and machined ID are applied by PID 1, before it begins with
> >> starting any units, hence *really* early on. Note though that actually
> >> /etc/machine-id is used as flag for "is /etc empty". If the file
> >> exists it is assumed that /etc is provisioned properly. If it is
> >> missing PID 1 will generate the machiend id and apply presets.
> >
> > An OS installer could put the machine-id into /usr just fine (and so
> > can I) and systemd could just get it from there if available before
> > generating a new one.
> >
> > It would be nice if the machine-id did not change during to a factory
> > reset: It is used in the logs and changing it will basically make
> > historical log data much harder to analyze. IIRC networkd also uses it
> > to generate persistent MAC addresses for containers and such.
> >
> > So far this seems to be the only critical piece of information that
> > can not get restored via tmpfiles.d.
> Thinking about this a bit longer: /usr does not seem like a good idea.
> The machine-id is supposed to be unique and usr-images are meant to be
> reused.
> Maybe provide a kernel command line option to force the machine-id if
> none is set yet?
I think this could be an option.  We currently check
/var/lib/dbus/machine-id, $container_uuid, and /sys/class/dmi/id/product_uuid.
I think that the first should work for your use case, since you keep /var.
But we also check some commandline option, this seems useful for some
use cases.


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