Re: Stateful system directories

[Efraim Flashner <efraim@flashner.co.il>]

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On Sat, Oct 19, 2019 at 11:08:57PM +0200, Ludovic Courtès wrote:
> Hello Efraim,
> 
> Efraim Flashner <efraim@flashner.co.il> skribis:
> 
> > Ignoring the directories in users' home directories, /var/lib/gdm has
> > been a source of pain on GNOME upgrades, and we still have some problems
> > with /var/cache/fontconfig and I believe there is something else with
> > permissions if you switch between ntp and openntpd. I actually have the
> > following snippet in my OS-config:
> >
> > ;; This directory shouldn't exist
> > (file-system
> >   (device "none")
> >   (mount-point "/var/cache/fontconfig")
> >   (type "tmpfs")
> >   (flags '(read-only))
> >   (check? #f))
> 
> I think that would work, or we could even make it a writable tmpfs?

I got angry with it and wanted to see if I could generate any error
messages. :) So far nothing. Of course there isn't a compelling reason
to really make it read-only if we recreate it each time, and it should
cut down on bugs for other directories.

> 
> (Somehow, I do have /var/cache/fontconfig, but never hard any problems
> with it.  It hasn’t been written to in months, and it’s only writable by
> root anyway.  Does that mean that people run into problem when they run
> GUIs as root?)

I have it too, not sure from what. I'm guessing some of the packages
which have fontconfig as an input get a dbus-something to create the
directory if it's missing.

> 
> > While we work on fixing these does it make sense to modify some of these
> > services to unconditionally recreate their home directories on
> > boot/activation?
> 
> Like /var/lib/gdm?  Maybe.  Or maybe ‘gdm-service-type’ could extend
> ‘file-system-service-type’ with a tmpfs for /var/lib/gdm?
> 

Sounds like a good idea. Would that also cause the directory to be
removed if gdm is removed? It should create a tmpfs and mount it over an
existing /var/lib/gdm, right?

> I suppose that might increase startup time a bit since it’d be
> rebuilding its cache every time.  Perhaps we’d also lose bits of state,
> no?

The increase in startup time should be negligible, and according to
rekado, who seems to run into GDM issues the most, removing /var/lib/gdm
is one of the first steps when upgrading gnome or debugging gdm issues.

> 
> Thanks,
> Ludo’.

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Efraim Flashner   <efraim@flashner.co.il>   אפרים פלשנר
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