My thanks to David Wright and Max Nikulin.
That was a good wake-up call. Most of my VMs are safe, but it was
interesting to learn what was really going on.
ForwardX11 was enabled for the ssh session. Initially I imagined
vncviewer (to the KVM host though ssh) was the one causing the problem,
but now it is clear that the ssh session to the VM was responsible for it.
This was the result of checking open tcp ports on the VM:
$ netstat -nlt
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
...
tcp 0 0 127.0.0.53:53 0.0.0.0:* LISTEN
tcp 0 0 127.0.0.1:6010 0.0.0.0:* LISTEN
$ echo $DISPLAY
localhost:10.0
It was also a good opportunity to learn about XPRA and test it.
Albert
On 2/17/23 22:15, David Wright wrote:
On Fri 17 Feb 2023 at 20:57:38 (-0500), Albert S. wrote:
Running “xrandr --size 800x600” on a virtual machine affected both
monitors on my workstation. That was completely unexpected and I am
wondering how to explain that.
Below you will find the detailed description.
[ … ]
But my real concern is how a xrandr command issued on a VM which is
running on another machine could affect the video of the client
machine used to access that VM.
I would appreciate an explanation for that.
The clue is in your use of the word "client". In fact, the "video of
the machine used to access that VM" is the X /server/. The
applications that you control on this machine, and others that you
connect to, which you thought were servers, are in fact the clients.
So, for example, I'm sitting at my All-in-One, running an X server as
usual. In a room down the hall, I have a laptop that's booted up, but
hasn't been used yet. It's sitting at a VC prompt waiting for someone
to log in. There's no X server running on it.
I've connected to the laptop with ssh from an xterm here on my A-i-O,
and typed into the /laptop/:
$ xrandr --output eDP --rotate right
and immediately, my screen blanks, comes back a second later, and
everything is sideways. When I type:
$ xrandr --output eDP --rotate normal
then normality is restored.
So I ran xrandr on the laptop, but xrandr is not concerned with that
machine, but only with the X /server/, running on my A-i-O.
https://en.wikipedia.org/wiki/X_Window_System
Cheers,
David.
