bug#35996: User account password got locked when booting old generation

["pelzflorian (Florian Pelz)" <pelzflorian@pelzflorian.de>]

It appears your patch fixes the issue.  I admire the speed at which
you write patches. :)  Thank you!

On Wed, Jun 05, 2019 at 11:54:23AM +0200, Ludovic Courtès wrote:
> Note that you’ll have to create a new “broken” generation with this
> patch (because we already know that the old one can corrupt
> /etc/shadow.)
>

I created a new working generation and then a new unbootable
generation with broken udevd args, both with all your patches.  I
rebooted the broken and then the working generation repeatedly twelve
times.  I waited varying amounts of time before doing Ctrl+Alt+Del in
the broken generation.  /etc/shadow is still in good health.

However:

On Tue, Jun 04, 2019 at 11:21:05PM +0200, Ludovic Courtès wrote:
> Indeed, ‘shepherd’ calls ‘disable-reboot-on-ctrl-alt-del’ (which
> disables “hard” reboots upon ctrl-alt-del and instead notifies it) after
> it has loaded its config file.

Is there a good reason shepherd calls disable-reboot-on-ctrl-alt-del
at the end?  I get recovering journal messages unless on the previous
boot I waited for the whole GDM to start (I can login on the TTY
before GDM has fully started), which takes a long time during which
users could change their mind and decide they do not want to boot.
(The Macbook is not fast anyway and Guix is even slower when booting
compared to Debian.)

Regards,
Florian