On Sat, May 15, 2021 at 07:33:45AM +0000, c.buhtz@posteo.jp wrote:
> Hello,
> 
> I am using
> 
> GNU Emacs 26.1 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.5) of
> 2021-01-31, modified by Debian
> 
> in Debian 10 (stable).
> 
> My question is if and how Emacs itself decide in which terminal
> emulation it opens when started via "emacs -nw" in a desktop
> environment (e.g. Xfce).
> And can I manipulate that?

You have to talk to your desktop environment for that. Emacs
takes the terminal it's started in -- it doesn't get to choose.

> The background of my question:
> When I open the context menu of a file in my Xfce filemanager Thunar
> the "Open with..." sub-context-menu offers me "Emacs (GUI)" and "Emacs
> (Terminal)".
> 
> The later opens emacs in a simple (and ugly) xterm.

C'mon. Xterm is the nicest terminal out there ;-)

(Actually, after trying several others for a while, I'm now
an extremely happy Xterm user. De gustibus...)

> The entry in that context menu referes to a .desktop-file
> (/usr/share/applications/emacs-term.desktop) with the line
> 
> 	"Exec=/usr/bin/emacs -nw %F"
> 
> xterm is not the default terminal. The default is
> "/usr/bin/terminator". I checked that via "update-alternatives --config
> x-terminal-emulator".
> 
> When I enter "emacs -nw" in my terminator window the emacs opens in
> that terminator window. So there is not xterm involved.

That's what Emacs does always.

> So it looks like that emacs ignores the systems default terminal.
> 
> What is the background of that behaviour and can I modify it?

There must be some option around in *your* desktop environment
to control which terminal you start a terminal application with.
Either in the .desktop file itself, or some default.

As I don't use a DE (I dropped that many years ago) I can't give
you more details.

Apparently, the freedesktop specification for .desktop entries [1]
hasn't a way to specify which terminal to use. So it must be either:

(a) your Emacs .desktop entry actually starts an Xterm and
   therein an Emacs (look into that). This would be something
   like

     xterm -e emacs -nw

   or thereabouts. This would be extremely silly (and somewhat
   authoritarian), but us computer folks are like that.

(b) your DE (you say it's "e.g. Xfce" ;-) somehow thinks you
   gotta like Xterm. No idea it honours the preferred alternative
   you set with "update-alternatives" (it should, but hey).

HTH

[1] https://specifications.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.html

 - tomás