[Discuss] Future of X11 (was Trying to connect to internet in Debian)

[richard.pieri at gmail.com (Rich Pieri)]

On Sun, 18 Jan 2026 17:07:41 -0800
Kent Borg <kentborg at borg.org> wrote:

> Question: Does it matter where the applications are running? 
> Specifically, can two remote windows coming from different clients
> (to use the odd X sense of the term) on different machines, see each
> other's activities on the same physical server (to again use the odd
> backwards sense)?

X11's use of server is not odd or backwards. X11's use is exactly the
same as every other server out there: a server is a program which
provides one or more services. It's the same as running Postfix and
mailx on the same machine -- the fact that Postfix is running locally
does not magically make it not a server. Anywho...

If the clients are using the same X11 server, are marked trusted by the
X11 SECURITY extension, and the clients have matching X11 auth keys
then in principle they can see each other's activity because that trust
is granted. See Dan's reply about what ssh -Y does; it's much more
detailed than mine and I made some invalid assumptions.

For example, I'm running an X11 server in front of me, and I have ssh
connections with X11 forwarding to my home server (call it aaa) and
something at my shell provider (call it bbb). Clients running on aaa
and bbb can see each other via my X server because trusted and keys.

This is not intrinsically bad. For example, if I want to copy-paste
between the two clients then both need access to the same shared
clipboard. I can copy-paste freely between the clients running on aaa
and bbb because they are trusted. If either or both were untrusted then
this would not work.

-- 
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