bug#44824: 27.1; Org export as pdf and open file does not open it

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Il 28/01/2021 04:02, Lars Ingebrigtsen writes:
> "gbiotti@gmail.com" <gbiotti@gmail.com> writes:
>
> > The same as using C-c C-e l o
> > "The default PDF program (okular) appears to open (i see the icon, but not
> > the window) and closes without showing anything."
> If I do
>
> $ xdg-open ./doc/lispintro/cons-2.pdf
>
> after `M-x shell', "Document Viewer" is opened as normal.
>
> You don't get any output from xdg-open or anything in the shell buffer?
>
> Glenn Morris <rgm@gnu.org> writes:
>
> > Ref eg https://debbugs.gnu.org/cgi/bugreport.cgi?bug=25234#8
> > https://bugzilla.gnome.org/show_bug.cgi?id=652262
> > https://gitlab.gnome.org/GNOME/glib/-/issues/1208
> > and others going back over a decade.
> > I think Emacs should have a PROBLEMS entry about this.
> Yeah, calling xdg-open (and expecting it not to exit) is a known
> problem, but here it seems that xdg-open doesn't even work from *shell*,
> which is very odd.

More info:

As per bug 25234, using 'M-! xdg-open /tmp/test.pdf', 'M-& xdg-open 
/tmp/test.pdf'
and 'M-& xdg-open /tmp/test.pdf && sleep 3' I get same results as reported.

If I try in eshell buffer 'xdg-open /tmp/test.pdf && sleep 3' my cursor 
blinks
with the Okular icon for a few seconds and then nothing happens.