Cleaning of $XDG_CACHE_HOME and $XDG_CACHE_HOME/thumbnails

[Benjamin Berg]

On Wed, 2020-02-26 at 14:22 +0100, Bastien Nocera wrote:
> On Wed, 2020-02-26 at 13:45 +0100, Benjamin Berg wrote:
> > Now, systemd-tempfiles can already clean up everything except for the
> > trash. And considering that $XDG_CACHE_HOME is non-essential by
> > definition, I think it might be sane to use systemd-tempfiles not only
> > to clean the thumbnails but the entirety of $XDG_CACHE_HOME in the
> > future.
> 
> It's not "non-essential", it's a cache, which can be regenerated, but
> it might be utterly costly to do so. Eg. there are 10 gigs of "cached"
> evolution mails in my ~/.cache, 5 gigs of jhbuild builddirs.
> 
> Nuking it is a last ditch scenario. You'd avoid backing it up on space
> constrained storage, but you'd want to avoid having to regenerate that
> cache in most cases.

I am *not* proposing to nuke these directories. I am proposing to nuke
them by default, and ask applications like evolution, jhbuild and
others to ship their own configuration.

This matches the behaviour of /tmp and /var/tmp on systemd managed
systems. In the simplest case, all evolution needs to do is ship a one
line file with:

x     %C/evolution

This file can even be installed to the users $XDG_CONFIG_DIR for
applications that might not be able to do it globally.

> <snip>
> > Is it reasonable to standardise on the systemd tmpfiles.d format?
> > Is it OK to clean $XDG_CACHE_HOME after a fixed time period by
> > default?
> 
> I'm guessing that's a no.
> 
> As for thumbnails, you'd probably get away with checking whether atime
> is actually set on that mount and cleaning up the ones that haven't
> been used.

Benjamin
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