bug#19795: Allow for stateless users and groups in GuixSD

[Ludovic Courtès]

Mark H Weaver <address@hidden> skribis:

> If we do this, I think we should take steps to prevent users+groups from
> being added, removed, group memberships changed, setting of passwords,
> etc, outside of 'guix system reconfigure'.  I think that users will be
> very unhappy with us if commands like 'passwd' and 'useradd' work as
> expected, but are undone the next time they update their system.

Just to be clear about the current situation: everything is stateless,
with the exception of passwords (‘reconfigure’ does not alter them) and
user accounts that are not removed (the crux of this report.)

Apart from passwords, any modification is undoed on the next
‘reconfigure’ or on the next reboot.  See notably e2b464b7, which took a
step to ensure that user account settings in the OS declaration are
fully honored.

In response to this bug report, I would just add activation code that
removes any unknown user accounts.

Thanks,
Ludo’.