XDG_RUNTIME_DIR permission check

[Thomas Kluyver]

On Mon, Jan 9, 2017, at 11:35 AM, Lennart Poettering wrote:
> That said, people do weird stuff with su/sudo. It might or might not
> make sense for apps to superficially check ownership of the dir before
> using it. However I am very sure apps should never try to "fix" it it
> doesn't match their expectations, as that most likely would make
> things worse, not better in such su/sudo setups.

We have had some issues where users report that XDG_RUNTIME_DIR is set
but not accessible, which I think was due to su/sudo inheriting
environment variables. Presumably in these cases, apps should behave as
though XDG_RUNTIME_DIR is not set, but it might be useful for the spec
to mention this possibility and an appropriate check for it.

Also, is it worth trying to recommend any fallback options when
XDG_RUNTIME_DIR is not set or not usable? As far as I know, there's no
other directory which offers the same guarantees, but we still want our
app to run. In our case, we create a private directory under
XDG_DATA_HOME, but we only use it for regular files, not named pipes or
anything.

Thanks,
Thomas